Highway Engineering_paul H.wright

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HIGH WAY ENGI

NEER ING FIFTH EDITION PAUL

PAQUETTE

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chapter five

TRAFFIC CHARACTERISTICS

A knowledge of traffic characteristics is useful to the highway engineer in developing highway and transportation plans, performing economic analyses, establishing geometric design criteria, selecting and implementing traffic con trol measures, and evaluating the performance of transportation facilities. Dozens of measures have been employed to describe the quality and quantity of traffic flow. In this chapter, information is presented on those flow characteris tics that fundamentally bear on the planning, design, and operation of highway and transport facilities: traffic speed, travel time, volume, and density. In a section on highway capacity, we will consider ways of estimating the ability of various highway facilities to accommodate traffic flow. Finally, we will describe the nature and severity of the highway accident problem and examine the causes of traffic crashes.

TRAFFIC FLOW CHARACTERISTICS 5-1 Speed and travel time Speed of travel is a simple and widely used measure of the quality of traffic flow. Basically, speed is the total distance traversed divided by the time of travel. Speed is commonly expressed in miles per hour or feet per second. Its reciprocal, travel time, is usually expressed in units of minutes per mile. There are three basic classes or measures of speed of travel: 1.

Spot speed.

2.

Overall speed.

3.

Running speed.

Spot speed is the “instantaneous” speed of a vehicle as it passes a specified point along a street or highway. There are, of course, practical difficulties in measuring instantaneous speeds since, by definition, speed is the distance traveled divided by the travel time. Spot speeds may be determined by man ually measuring the time required for a vehicle to traverse a relatively short specified distance. A variety of electromechanical and electronic devices are commonly employed to measure spot speeds. Such devices typically involve some sort of vehicle detectors (e.g., pneumatic tubes) that actuate and stop a timing mechanism, the time of travel or speed being printed on a tape or recorded on a graph. Radar meters have also been widely used by traffic engineers and enforcement officers to measure spot speeds.

100 TRAFFIC CHARACTERISTICS The average of a series of measures of spot speeds can be expressed in two ways, as a time-mean speed and a space-mean speed. Time-mean speed is the arithmetic mean of speeds of all vehicles passing a point during a specified interval of time. The time-mean speed is

u, =------------n

(5-1)

where Uj ~ observed speed of Ah vehicle n = number of vehicles observed The space-mean speed is the arithmetic mean of speeds of vehicles occu pying a relatively long section of street or highway at a given instant. It is the average of vehicle speeds weighted according to how long they remain on the section of road. The space-mean speed is us

nd (5-2)

where d = length of roadway section ti = observed time for the ?ih vehicle to travel distance d Space-mean speed and time-mean speed are not equal. In fact, Wardrop (1) has shown that --+

U, — u x + —

ux where of = variance of the space distribution of speeds

(5-3)

For general-purpose usage, no distinction is normally made between timemean and space-mean speeds. For theoretical and research purposes, the type of mean should be specified. Overall speed and running speed are speeds over a relatively long section of street or highway between an origin and a destination. These measures are used in travel time studies to compare the quality of service between alternative routes. Overall speed is defined as the total distance traveled divided by the total time required, including traffic delays. Running speed is defined as the total distance traveled divided by the running time. The running time is the time the vehicle is in motion; time for stop-delays is excluded. Overall and running speeds are normally measured by means of a test vehicle that is driven over the test section of roadway. The driver attempts to travel at the average speed of the traffic stream or to “float” in the traffic stream, passing as many vehicles as pass the test vehicle. A passenger uses a stopwatch to record time of travel to various previously chosen points along the course. Distances are usually recorded by the vehicle’s odometer. The test drive is repeated several times and the average travel time is used to compute the overall and running speeds. Spot speeds vary with time, location, and environmental and traffic condi tions. Since 1942, the average speed on main rural highways has generally increased, rising from about 40 mph in 1944 to 50 mph in 1951 and 60 mph in 1968. Following a petroleum embargo and the subsequent imposition of a nationwide 55

Traffic Flow Characterist ics 101 mph speed limit, the average speed on main rural highways decreased to 55.7 mph in 1983. Speeds vary with the quality of traffic service, being generally higher along expressways and other well-designed facilities and during times when traffic congestion is not a factor. Oppenlander (2) found that, mean spot speeds along twolane rural highways were positively related to lane width and mini mum sight distance and negatively related to degree of curvature, gradient, and the number of roadside establishments per mile of highway. At a given time and location, speeds are widely dispersed and can gener ally be represented by a normal probability distribution. As Figure 5-1 illus trates, the range of speeds decreases with increase in traffic volume.

5 “2 Traffic volume and rate of flow Traffic volume is defined as the number of vehicles that pass a point along a roadway or traffic lane per unit of time. A measure of the quantity of traffic flow, volume is commonly measured in units of vehicles per day, vehicles per hour, vehicles per minute, and so forth. Two measures of traffic volume are of special significance to the highway engineer: average daily traffic (ADT) and design hourly volume (DHV). The average daily traffic is the number of vehicles that pass a particular point, on a

Spot speed (mph)

FIGURE 5-1 Typical distribution of passenger car speeds in one direction of travel under ideal uninterrupted flow conditions on freeways and expressways. (Courtesy Transportation Research Board.)

roadway during a period of 24 consecutive hours averaged over a period of 365 days. ADT is a fundamental traffic measurement needed for the de termination of vehicle-miles of travel on the various categories of rural and urban highway systems. ADT values for specified road sections provide the highway engineer, planner, and administrator with essential information needed for the determination of design standards, the systematic classification of highways, and the development of programs for improvement and maintenance. Vehiclemiies values are important for the development of high way financing and taxation schedules, the appraisal of safety pro grams, and as a measure of the

102 TRAFFIC CHARACTERISTICS service provided by highway transportation. (3) It is not feasible to make continuous counts 365 days a year along every section of a highway system. Average daily traffic values for many road sections are therefore based on a statistical sampling procedure described in Chapter 6. The design hourly volume is a future hourly volume that is used for design. It is usually the 30th highest hourly volume of the design year. Traffic volumes are much heavier during certain hours of the day or year, and it is for these peak hours that the highway is designed. It has been found that, for the United States as a whole, traffic on the maximum day is approximately 233 percent of the annual average daily I raffie and traffic volume during the maximum hour is approximately 25 percent of the annual average daily traffic. In order to design a highway properly, it is necessary to know the capacity that must be provided in order to accommodate the known traffic volume. The relation between peak hourly flows and the annual average daih traffic on rural highways is shown in Figure 5-2. Experience has indicated that it. would be uneconomical to design the average highway for an hourly volume greater than that which will be exceeded during only 29 hr in a year. The hourly traffic volume chosen for design purposes, then, is that occurring during the “30th highest hour.” An approximate value of the 30th highest hour can be obtained by applying an empirically based percentage to the future ADT. The thirtieth highest hour, as a percentage of the average daily traffic, ranges from 8 to 38 percent, with an average for the United States of 15 percent for rural locations and 12 percent for urban locations. Early studies of U.S. traffic indicated that the relationship between the thirtieth highest hour and the annual average daily traffic remained un changed from year to year. However, later studies suggest that the thirtieth highest hour factor has a tendency to decline slightly with the passing of time. If this trend continues, appropriate adjustments will have to be made in the design hourly volume for any future year. On a given roadway, the volume of traffic fluctuates widely with time.

Traffic Flow Characterist ics 103

NUMBER OF HOURS IN ONE YEAR WITH TRAFFIC VOLUME GREATER THAN THAT SHOWN

FIGURE 5-2 Relation between peak hourly flows and annual average daily traffic on rural highways. {Courtesy Federal Highway Administration.)

Figures 5-3, 5-4, and 5-5 illustrate the variations in volume that occur with time of day, day of the week, and season of the year. These variations tend to be cyclical and to some extent predictable. The nature of the pattern of variation depends on the type of highway facility. Urban arterial flow is characterized by pronounced peaks during the early morning and late afternoon hours, due primarily to commuter traffic. The peaking pattern is not generally evident on weekends, and such facilities experience lowest flows on Sundays. Rural high ways tend to experience less pronounced daily peaks, but they may accommo date heaviest traffic flows on weekends and holidays because of recreational travel. Highway facilities generally must accommodate heaviest flows during the summer months. Peaks typically occur during July or August. As might be expected, the seasonal fluctuations are most pronounced for rural recreational routes. The term rate offlow accounts for the variability or the peaking that may occur during periods of less than 1 hr. The term is used to express an equiva lent hourly rate for vehicles passing a point, along a roadway or for traffic during an interval less than 1 hr, usually 15 min (4),

TRAFFIC CHARAC'FFRISTICS

4 AM

HOUR OF DAY

0 AM

12 N

4 PM

8 PM

Hourly variations of volume of traffic on an average weekday. (Courtesy rtmem of Transportation.)

TRAFFIC CHARAC'FFRISTICS

SUN MON TUE WED THU PR] SAT FIGURE 5-4 Traffic volume fluctuation by day of week. {Courtesy Georgia Department of Transportation.)

'The distinction between volume and rate of flow may be illustrated by an example. Suppose the following traffic counts were made during a study period of 1 hr:

Time Period 8:00 — 8:15 8:15 — 8:30 8:30 —8:15 8:45-9:00 Total

Number of Vehicles 1000 1 100 1000 900 4000

Rale of I‘loir (vehicles! hr) 4000 4400 4000 3600

The total volume is the sum of these counts or 4000 vehicles/hr. The rate of flow varies for each 15-min period and during the peak period is 4400 vehicle s/hr. Note that 4400 vehicles did not actually pass the observation point during the study hour, but they did pass at that rate for one 15-min period.

TRAFFIC CHARAC'FFRISTICS

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC FIGURE

5-5 Monthly variation in traffic volume. (Courtesy

Georgia Depai uncut of Transportation.)

Consideration of peak rales of How is of extreme importance in highway capacity analyses.* Suppose the example roadway section is capable of han dling a maximum rate of only 4200 vehicles/hr. In ot her words, its capacity is 4200 vehicles/hr. Since the peak rate of flow is 4400 vehicles/hr, an extended breakdown in the flow would likely occur even though the volume, averaged over the full hour, is less than the capacity. The Highway Capacity Manual (4) uses a peak hour factor to relate peak rates of flow to hourly volume. The peak hour factor is def ined as t he ratio of total hourly volume to the maximum rate of flow within the hour. If there was no variability in flow rate during the hour, the peak hour factor would be 1.00. Typical peak hour factors for two-lane roadways range from about 0.83 to 0.96.

5-3 Traffic density Traffic density, also referred to as traffic concentration, is defined as the average number of vehicles occupying a unit length of roadway at a given instant. It is generally expressed in units of" vehicles per mile. As Section 5-5 ;i:

Highway capacity analyses are discussed in more detail in Section 5-6.

Traffic How Characteristics 105

indicates, traffic density bears a functional relationship to speed and volume. Density has not been extensively employed in the past by highway and traffic engineers to describe traffic How; however, it is now recommended as the basic parameter for describing the quality of flow along freeways and other multi lane highways, ft has also been the foetus of a number of theoretical and analytical studies.

5-4 Spacings and headways There are many situations that engineers encounter for which it is necessary to consider the behavior of individual vehicles in the trail test ream rather than the average traffic stream characteristics. Such situations include calculating the probability of delay and average delay for vehicles or pedestrians crossing a traf fic stream and predicting the length of waiting lines at toll booths, traffic signals, arid entrances to parking facilities. 'Two measures are of fundamental importance in such calculations: spacing and time-headway between succes sive vehicles. The spacing is simply the distance between successive vehicles, typically measured front from bumper to from bumper. It is the reciprocal of density. Time-” headway is the time between the arrival of successive vehicles at a specified point and it is the reciprocal of volume. For many light traffic situations, traffic can be described by the Poisson probability distribution. 'The equation for the Poisson distribution is wV"' P(x) --------— x!

(5-4)

where P{x) = the probability that exactly x randomly arranged vehicles will be observed in a unit length of road, or the probability of arrival of exactly x vehicles in a unit length of time m ~ T//3600 = the average number of vehicles arriving in an interval of length L V = traffic volume (vehicles/in') I = length of time interval (sec) EXAMPLE. 5-1. The Poisson Distribution Consider the following example, which has been taken from Ref. 5. 'The number of vehicles arriving along a Los Angeles street was recorded for each of 120 50-sec intervals. During 9 of the intervals, no vehicles arrived; during 16 intervals exactly one vehicle arrived; and so forth. See Table 5-1. 5.067

The average number of arrivals is Vi 368(60) >>l6600 ~ (3.67) V" - 5 '

5600 P{0) - -------------------------- 0.047 0! 1 (3.67) tf“ s - o
106

TRAFFIC: CHAR ACTERISTICS

TABLE 5-1 EXAMPLE DATA FOR THE POISSON DISTRIBUTION Traffic Arrivals; 30-sec Intervals (Durfee Avenue, Northbound} Number of cars per interval X,

Observed Total cars frequency"f observed j]Xt

0

90

1 2 3 4

16 16

5 6 7 B >9

10 50

30 60 22 66 10 76 3 18 7 49 3 24 19

Probability of X„. PfXj '

'Theoretical frequency If

0.047 0.143 0.219 0.224 0.172

5.6 17.2 26.3 26.9

0.105 0.054 0.023 0.009

12.6 6.5

0.002

'Total

20.6

2.8 LI 0.4 120.0

120 368 368 tn — = 3.067 120

1.000 e~m - 0.047

T, - i 20 (P(Xj) ■'Data l)y courtesy of Los Angeles County Road Department. Son roc P O ISSO II and Other Distribution* in Traffic, Luo Foundation for Transportation. Saugatuck, Conn. (197!).

Other probabilities are shown in Table 5-1. The theoretical frequencies corre sponding to the probability / ( X j ) are J

If - 120 P(x,) F(i = 120(0.047) = 5.6 intet'vals etc. Corresponding to the Poisson counting distribution lor free-flow condi tions is the negative exponential gap or headway distribution. The equation is P(g^T) =

(5-5)

where (P(g > 7') — the probability of a headway equal to or greater than T sec 'The value e is the Naperian logarithmic base and V' and T are as previously defined. EXAMPLE 5-2. The Negative Exponential Distribution Given the conditions described in Example 5-1, estimate the percentage of a randomly chosen group of gaps that will be greater than 10 sec.

Traffic Flow Characterist ics 107

Thirty-six percent of (he gaps will be greater than 10 see. It should be emphasized that die Poisson and negative exponential distri butions are applicable to random or free-flow traffic situations. More complex distributions have been proposed to describe a wider variety of traffic flow conditions. References 5 and 6 give detailed descriptions of many counting and headway distributions.

5-5 Speed “volume-density relationships

(5-6)

'The relationship betaveen traffic speed, volume, and density is shown by the f a n d amen t a 1 eq u a tio n q = kus where q — average volume or llow (vehicles/hr) k — average density or concentration (vehicles/mile) u, — space-mean speed (mph) Although a number of theoretical and analytical speed-density relationships have been published, the exact shape of the k-w, curve has not been conclusively established. A model proposed by Greenshields (7) assumed a linear relationship between speed and density. With that assumption, a parabolic volume-density model results. 'The Greenshields model is illustrated by Fig ure 5-6 along with the corresponding relationships between speed and volume and volume and density. The curves represent a hypothetical situation with a maximum (or mean-free) speed of 50 mph and a maximum density of 175 vehicles/mile. Let us consider three key points on the curves shown in Figure 5-6. Point A represents a low-density, high-speed .situation. Low volumes exist because few vehicles are on the road. Point B is the point of maximum llow. For this condition, intermediate levels of speed and density occur. Point C represents the worst possible type of llow' situation, with maximum density occurring and speeds (and volume) approximating zero. Empirical research has indicated that speed decreases exponentially with increases in density. Figure 5-7 show's empirical data collected in the Lincoln Tunnel to which a logarithmic flow-concentration curve lias been fitted. The equation is

108 TRAFFIC CHARACTERISTICS

(5-7) where = speed at. maximum flow kj = maximum density

Traffic Flow Characterist ics 109

Density k (veh./mi)

Volume q (veh./hr)

FIGURE 5-6 Theoretical flow, density, speed relationships.

110 TRAFFIC CHARACTERISTICS

k (veh./mi) FIGURE 5-7 Logarithmic fknv-concenlnukm diagram, (Courtesy Transportation Research Board.)

For the data represented by Figure 5-7, um = 17.2 vehicles/hr and kj = 228 vehicles/mi.

5-6 Highway capacity Even with ideal roadway conditions (e.g., a test track), traffic volume tends to reach a maximum point at a relatively low speed. (See Figure 5-8.) This phenomenon, which is puzzling to the casual observer, results from the fact that spacing allowed by the average driver when trailing another vehicle in creases nonlinearly with increases in speed (8). Stated another way, traffic density decreases exponentially with increases in speed, as Figure 5-9 illus trates. Referring to Eq. 5-6, increasing speed tends to increase volume, but that effect is offset by concomitant decreases in density. Another factor limiting the number of vehicles passing a point is interfer ence between vehicles in the traffic stream. This effect is especially noticeable along twolane roads. With a low traffic volume, the vehicle operator has a w'ide latitude in selecting the speed at which he or she wishes to travel. As traffic volume increases, the speed of each vehicle is influenced in a large measure by the speed of the slower vehicles. As traffic density increases, a point is finally readied w'here all vehicles are traveling at the speed of the slower vehicles. This condition indicates that the ultimate capacity has been reached. The capacity of a highway is therefore measured by its ability to accommodate traffic and is usually expressed as the number of vehicles that can pass a given point in a certain period of time at a given speed. Roadways, of course, are not ideal, and in hightvay capacity estimates allowances must be made for prevailing roadway and traffic conditions that inhibit the ability of a road to accommodate traffic. In determining highway capacities for uninterrupted flow conditions, the general procedure, described below', is to begin with capacities corresponding to ideal conditions and to apply appropriate empirically based adjustments for prevailing roadway and traffic conditions. The capacity of a given section of roadway, either in one direction or in both directions for a two-lane or three-lane roadway, may be defined as the

Traffic Flow Characterist ics 111

Flow (veh,/hr)

FIGURE 5-8 Experiim’»i;il speed-How relaiionshipon test track with straight roadway section. (Courtesy Transportation Research Board)

maximum hourly rate at which vehicles can reasonably be expected to traverse a point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic, and control conditions (4). Although the maximum number of vehicles that can be accommodated remains fixed under similar roadway and traffic conditions, there is a range of lesser volumes that can be handled under differing operating conditions. Operation at capacity provides the maximum volume, but as both volume and congestion decrease there is an improvement in the level of service. Level of service is a qualitative measure that describes operational condi tions within a traffic stream and their perception by drivers and/or passengers (4). Six levels of service, A through F, define the full range of driving conditions from best to worst, in that order. These levels of service qualitatively measure the effect of such factors as travel time, speed, cost, and freedom to maneuver, which, in combination with other factors, determine the type of service that any given facility provides to the user under the stated conditions. With each level of service, a service flow rate is defined. It is the maximum volume that can pass over a given section of lane or roadway while operating conditions are main tained at the specified level of service. The levels of service have traditionally been based on relationships involv-

112 TRAFFIC CHARACTERISTICS

Concentration (veh,/mi)

FIGURE 5-9 Spced-concemnttion curve for straight track at British Road Research Laboratory. (Courtesy Transportation Research Board)

ing operating speed and voluine-to-capacitv ratio. Figure 5-10, a graphical representation of the level-of-service concept, shows that, as the operating speed on a facility increases, the higher levels of service are attained; on the other hand, as the volume-to-capacity ratio increases, the facility tends to operate at a lower level of service. Level A represents free flow at Sow densities with no restrictions due to traffic conditions. Level B, the lower limit of which is often used for the design of rural highways, is the zone of stable flow with some slight restriction of driver freedom. Level C denotes the zone of stable flow with more marked restriction on the driver’s selection of speed and with reduced ability to pass. The condi tions of Level I) reflect little freedom for driver maneuverability, and. while the operating speeds are still tolerable, this region approaches the condition of unstable flow. Low operating speeds and volumes near or at capacity indicate level of service E, which is the area of unstable flow. Level F is the level of service provided by the familiar traffic jam, with frequent interruptions and breakdown of flow, as well as volumes below capacity coupled with low operating speeds. The operational parameters used to determine the level of service diff er with the type of facility. These parameters or “measures of effectiveness”

Traffic Flow Characterist ics 113

VOLUME/CAPACITY RATIO FIGURE 5-10 Genera! concept of relationship of leve! of service to operating speed and volume/capacity ratio (not to scale). {Courtesy Transportation Research Board.)

TABLE 5-2

MEASURES OF EFFECTIVENESS FOR LEVEL OF SERVICE DEFINITION Type of Facility

Measure of Effectiveness

Units

Density Average travel speed Flow rate

Passenger cars per mile per latte Miles per hour Passenger cars per hour

Density Percent time delay Average travel speed

Passenger cars per mile per lane Percent Miles per hour

Uninterrupted Flow Facilities

Freeways Basic freeway segments Weaving areas Ramp junctions M u! v i I a n e highw ays Two-lane highways Interrupted Flow Facilities

Signalized intersections D n sign a 1 i zed i n ter.seciion s Arteriais Transit Pedestrians

Average individual stopped delay Reserve capacity Average travel speed Load factor Space

Seconds per vehicle Passenger cars per hour Miles per hour Persons per seat Square feet per pedestrian

SouRCK: Highway Capacity Manual Transport at ion Research Board Special Report No. 209 (1985),

describe the operating quality for each type of facility. Table 5-2 sets out the measures of effectiveness that best define the level of service for each facility type. The Highway Capacity Manual The Highway Capacity Manual (4) is the authoritative guide for the perfor mance

114 TRAFFIC CHARACTERISTICS of highway capacity analyses. The manual reflects over 20 years of comprehensive research by a number of research agencies. This 487-page document was prepared under the guidance of the Transportation Research Board’s Committee on Highway Capacity and Quality of Service. The procedures described in the Highway Capacity Manual cover a wide range of facilities, including streets and highways as well as facilities for transit, pedestrians, and bicyclists. As Table 5-2 illustrates, capacity analyses are per formed for two general categories of facilities, those with uninterrupted flow and those with interruptedflow. Uninterrupted flow facilities include two-lane high ways, freeways, and other multilane highways. The traffic flow conditions on such facilities result from interactions among vehicles in the traffic stream as well as between vehicles and the physical and ambient characteristics of the roadway. Interrupted flow facilities generally have traffic control devices that cause periodic interruptions of traffic flow. Examples of such facilities are signalized and two-way and four-way STOP-controlled intersections. The capacity of interrupted flow facilities is limited not only by the physical features of the roadway space but also by the portion of time that is available for various components of traffic flow. Factors affecting capacity, service flow rate, and level of service Many of the procedures described in the Highway Capacity Manual are based on simple tables or graphs for specified standard conditions, which must be adjusted to account for prevailing conditions different from those specified. The conditions so defined are often descibed in terms of ideal conditions. Ideal conditions for uninterrupted flow facilities include 1, Twelve-foot lane widths. 2, Six-foot clearance between the edge of travel lanes and the nearest ob structions by objects at the roadside or in the median. 3. A 70 mph design speed for multi lane highways and 60 mph design speed for two-lane highways. 4. All passengers cars in the traffic stream (4). An ideal signalized intersection approach has 1. Twelve-foot lane widths. 2. 3. 4. 5. 6. 7.

Level grade. No curb parking allowed on the intersection approaches. All passenger cars in the traffic stream. No turning movements at the intersections. Intersection located outside the central business district. Green signal available at all times (7).

Since prevailing conditions are seldom ideal, computations of capacity, service flow rate, or level of service must be adjusted to account for departures from the ideal. Prevailing conditions may be grouped into three categories: roadway, traffic, or control conditions. Roadway factors include 1. 2. 3. 4. 5.

The type of facility and its development environment, Lane widths. Shoulder widths and/or lateral clearances. Design speed. Horizontal and vertical alignments.

Traffic Flow Characterist ics 115 Traffic conditions refer to the types of vehicles using the facility and how the traffic llow is distributed by lane use and direction. It is well known that larger and heavier vehicles have an adverse effect on traffic flow in a number of ways. Capacity analyses account for the impacts of trucks, buses, and recrea tional vehicles, utilizing the results of empirical studies that have quantified these effects. In addition to the distribution of vehicle types, the effects of two other traffic characteristics on capacity, service flow rates, and level of service must be considered. Directional distribution has a significant impact on the operation of twolane rural highways. Capacity generally declines as the directional split becomes unbalanced. For multilane highways, capacity analysis procedures focus on a single direction, that of the peak rate of flow. Lane distribution must also be considered for multilane facilities. Normally, the shoulder lane of a multilane facility carries less traffic than other lanes, and analysis procedures must account for these differences. For interrupted flow facilities, the control of the time available for move ment of each traffic flow is of utmost importance in determining capacity, service flow rates, and level of service. Of greatest importance is the control of such facilities by the traffic signal. Signalized operations are affected by the type of signal in use, the phasing, the allocation of green time, and the lengt h of cycle. STOP and YIELD signs also affect capacity, but. in a different way. The: STOP or YIELD sign assigns the right-of-way permanently to a major street, while a signal assigns designated times when specific movements are permitted, A complete treatment of highway capacity analyses is beyond the scope of this book. Two examples, one each for uninterrupted and interrupted flow, are given to illustrate the general approach used for such analyses. General methodology for capacity analysis for freeway segments With controlled access, limited ramp locations, and no fixed interruptions of traffic flow, freeways operate under the purest form of uninterrupted flow. A capacity analysis of a freeway segment begins with a recognition that a maximum service flow rate per lane exists for each ievel of service. The various

Traffic Flow Characteristic;;; 116 levels of service for freeways are defined by the density, expressed in passenger cat's per mile per lane. Suggested maximum service flow rates, ATS7p, are shown in 'Table 5-3. These rates, which represent, ideal conditions, must be adjusted to ac count for any prevailing conditions that are not ideal and to reflect the number of lanes in one direction on the freeway segment. The service flow rate for the specified level of service and prevailing conditions is computed by using correc tion factors, as the following equation demonstrates, ,Sb, = A'lSP j x A T x j w; x fnv ^ j p

(5-8)

where SF, — service llow rate for level of service i under prevailing roadway and traffic conditions for N lanes in one direction (vehicles/hr) N = number of lanes in one direction of the freeway /w “ factor to adjust for the effects of restricted lane widths and/or lateral clearances J HV factor to adjust for the effect of'heavy vehicles (trucks, buses, and recreational vehicles) in the traffic stream fp = factor to adjust for the effect of driver population 'The factor/w is based on the lane width, the number of freeway lanes, the distance to roadside obstructions, and whether obstructions are present on both sides of the freeway. 'Table 5-4 gives recommended adjustment factors for a range of lane widths and lateral clearances.

TABLE 5-3

LEVELS OF SERVICE (LOS) FOR BASIC FREEWAY SECTIONS WITH DESIGN SPEEDS OF 60 AND 70 MPH 70 mph Design Spec >d

LOS A

Density (passenger Speed" cars! mile per lane {mph) < 12 a 60

60 mph Design Speed

MSFh (passenger cars/ vie hr per lane) 0.35 700

Speed" (mph)

—

v/c

MSF'1’ (passenger car. hr per lane)

—

—

B

< 20

& 57

0.54

1,100

a 50

0.49

3,000

C D

< 30 < 42

a 54 a 46

0.77 0.93

1,550 1,850

a 47 a 42

0.69 0.84

1,400 1,700

E F

< 07 > 67

a 30 < 30

1.00 C

2,000 G

a 30 < 30

TOO

2,000

:|

Average travel speed. ’’Maximum service flow rate per lane under ideal conditions. (Note: All values of MSF are rounded to the nearest 50 passenger cars/hr.) "Highly variable, unstable. Sourcic: IIighum Capacity Manual. Transportation Research Board Special Report No. 209 (1985).

Traffic Flow Characterist ics 117

TABLE 5-4

ADJUSTMENT FACTOR FOR RESTRICTED LANE WIDTH AND LATERAL CLEARANCE A djustmenl Factor fr Distance from Traveled Pavement (fO

>6 5 4 3 2 1 0

, for Lane Width (ft)

Obstructions on One Side of Roadway 12

11

1.00 0,99 0.99 0.98 0.97 0.93

0.97 0.96 0.96 0.95 0.94 0.90

0,90

0.87

10

Obstructions on Both Sides of Roadway 9

4-Lane Freeway (2 Lanes Each Direction) 0.91 0.81 0.90 0.80 0.90 0.80 0.89 0.79 0.79 0.88 0.85 0.76 0.82

0.73

12

11

10

1.00 0.99 0.98 0.96 0.94 0.87

0.97 0.96 0.95 0.93 0.91 0.85

0.91 0.90 0.89 0.87

0.81

0.79

0.86 0.80 0.74

9

0.81 0.80 0.79 0.77 0.76 0.71 0.66

6 - or 8- Lane Freeway >6 5 4 3 2 1 0

1.00 0,99 0.99 0.98 0.97

(5 or 4 Lanes Each Direction) 0.96 0.89 0.78 0.95 0.77 0.88 0.95 0.77 0.88 0.94 0.87 0.76 0.93 0.87 0.76

LOO 0.99 0.98 0.97 0.96

0.96 0.95 0.94 0.93 0.92

0.89

0.95 0.94

0.92 0.91

0.93 0.91

0.89 0.87

0.83

0.86 0.85

0.75 0.74

0.88 0.87 0.86 0.85 0.81

0.78 0.77 0,77 0.76 0.75 0.72 0.70

‘‘Certain types of obstructions, high-type median barriers in particular, do not have any deleterious effect on traffic flow, judgment should be exercised in applying these factors. Sou rciu Highway Capacity Manual. Transportat ion Research Board Special Report No. 209 (1985),

The factor/ H V is used to account for the effects of trucks, buses, and recreational vehicles in the traffic stream. The factor depends on the terrain, specifically the length and magnitude of up grades, and the mix of vehicles in the traffic stream. Heavy vehicles, because of their restricted maneuverability, reduce the number of vehicles that a facility can handle. This reduction is represented by the term passenger-car equivalent, which indicates the equivalent number of passenger cars that have been displaced by the presence of each truck, bus, or recreational vehicle. Passenger-car equivalents for heavy trucks and buses are shown in 'Tables 5-5 and 5-6, respectively. The Highway Capacity Manual (■4) lists similar values for recreational vehicles. By using passenger-car equivalents such as those shown in Tables 5-5 and 5-6, the adjustment factor for heavy vehicles can be computed by the following equation: /hv = 1/[1 + PT(ET - 1) + PR(ER " 1) + Pz(EB - 1)]

(5-9)

118 TRAFFIC CHARACTERISTICS

TABLE 5-5

PASSENGER-CAR EQUIVALENTS Passenger FOR HEAVY -Car TRUCKS, Equivalent, E300,,LB/HP jar Percentage of Trucks 4-Lane Freeways Grade Length0 (%) (miles) <\ 1

2

8

4

2

4

5

6

8

10

29

2

4

.5

b

5

10

15

Ail 0-'/i l /\ - V‘i \G- % ■%-l 1 -1 'A > I fy 0“!/i

2 2 3 4 5

2 2 3 4 4 5 5 4

2 2 3 4 4 5 5 4

2 2 3 4 4 5 5 3

2 2 3 3 3 4 4 3

2 2 3 3 3 4 4 3

2 2 3 3 3 4 4 3

2 2 3 3 3 3 3 3

2 2 3 4 5

2 2 3 4 4 5 5 4

2 2 3 4 4 5 5 4

2 2 3 3 4 4 5 3

2 2 3 3 3 4 4 3

2 9 3 3 3 4 4 3

2 2 3 3 3 3 3 3

:

7 8 8 9

6 6 6 7 7 5 7

6 6 6 7 7 5 7

5 5

4 5 ,5

4 4 5

6 6 4 5

6 6 4 5

4 4 5 5 5 4 5

4 4 5 5 5 3 5

7 8 8 9

5 6 6 7 7 5 7

5 6 6 7 7 5 7

5 6 6 6 6 5

4 5 5 5 5 4 5

4 5 5 5 5 4 5

4 4 5 5 5 4 5

4 4 5 5 5 3 5

6 7

6 7

8 8 9 5

5

5

5

5

8 4

6 7 7 4

7

8 4

6 7 7 4

6 7 4

6 7 4

6 7 3

6 7 3

6 7

6 7

6 7

6 7

8 9

7 9

5 7

5

5

5

8 9 5 7

8 9 5 7

8 9 5 7

8 9 5 7

6 7

8 5

8 5

8 5

11 13 6 9

11 13 6 9

11 13 6 9

10 10 6 8 11 14 7

6 7

11 13 6 9

10 10 6 8 11 14 7

6 7

6 9

6 9

6 9

6 9

12 5

11 5

11 5

11 5

18

18

18

18

10 17

10 17

8 15

8 14

8 14

8 14

A-A

%-l 1 _ 11/, > 1 'A O-'/i

6

6 7 4

10 6 9

6 7 7 5 6 7

12 13 14 7

8 9

8 9

10 5

10 5

12 13

8 9

8 9

'■'/>-1 >1 O-'A { A-V'i

15 17

10 12 6 9

10 12 6 9

Vi—y,

20 22 9

15

15

6 8 14

17 7

17 7

16 7

17

12 22

12 22

11 21

%-I >1 0-*/, l/t - '/>

5

6~~8 Lane Freeways

>% O-'A >'A

8 13

28

8 9 5 7 8 9 TO

6 7 4

10 6 8 10 11 12 7 10 11 12 13 8 11 14 17 9 13 20

8 9 5

6 6 7 8 5 6 8 9 9 6 7 10 13 6 9 16

8 8 5

"If a length of grade fails on a boundary condition, the equivalent from the longer grade category is used. For any grade sleeper than the percentage shown, use the next higher grade category.

SOURCE:

Highway Capacity Manual. Transportation Research Board Special Report No. 209 (1985), where f hv = adjustment factor for the combined effect of trucks, re creational vehicles, and buses on the traffic stream E-y,En,En — passenger-car equivalents for trucks, recreational vehicles, and buses, respectively Ey, Pr, P\\ — proportion of trucks, recreational vehicles, and buses, re spectively, in the traffic stream

20 9 2 3 3 3 3 3 3

Traffic Flow Characterist ics 119

TABLE 5-6 PASSENGER-CAR

EQUIVALENTS FOR BUSES Grade (%)

Passe tiger-Car Equivalent,

EH

0-3

1.6

4" 5" 6°

1.6 3.0 5.5

■'Use generally restricted to grades more than !/i mile long. Set U rce. //ighway Capacity Manna L Transportation Research Board Special Report No. 209 (1985).

It is known that certain types of traffic, such as weekend and recreational traffic, use freeways less efficiently than weekday or commuter traffic. Little research has been done on this effect, but it is known that capacities tend to be lower on weekends, particularly in recreational areas. Lacking local data, considerable engineering judgment must be exercised in making an adjust ment for the character of the traffic stream. 'The Highway Capacity Manual suggests that an adjustment factor fP ranging from 0.75 to 0.90 be used to account for this effect, EXAMPLE 5-3. Capacity of a Basic Freeway Segment, (a) Determine the service flow rate with level of service C for a section of a four-lane freeway (two lanes in each direction) with II-ft lanes and obstructions 5 ft from traveled pavement on one side of the roadway, The section has a 4 percent gradient 0,8 mile long. It is to accommodate 12 percent heavy trucks, 6 percent buses, and no recreational vehicles. Based on local studies, an adjustment factor for the character of the traffic stream, /p, of 0.90 is indicated. The design speed is 70 mph. (b) What is the capacity of the segment (density = 67 passenger cars per mile per lane)? (c) Estimate the average travel speed that corresponds to the capacity. Solution to Fart (a). From Table 5-3, the maximum service How rate for LOS C is 1550 passenger cars/hr per lane. The service flow rate for LOS C is computed by Eq. 5-8, From Table 5-4, the factor to adjust for the effects of lane width and lateral clearances is/w = 0,96, 'To adjust for the effect of heavy vehicles, passenger-car equivalents for trucks and buses are obtained from Tables 5-5 and 5-6, respectively: ET = 8

E K = 1.6

By Eq. 5-9, the heavy vehicle factor /hv = I/[l + 0.12(8 - 1) + 0 + 0.06(1.6 - 1)] - 0.53 JV = 0.90 (given) By Eq. 5-8, the service flow rate SFC = 1550 x 2 x 0.96 x 0,53 x 0.90 = 1420 vehicles/hr Solution to Part (b). The capacity corresponds to the critical density of 67 passenger

120 TRAFFIC CHARACTERISTICS

cars/mile and from Table 5-3 is 2000 passenger cars/hr per lane (ideal conditions). Eor the prevailing conditions, the capacity is SFE = 2000 x 2 x 0.96 x 0.53 x 0.90 - 1832 vehicles/hr Solution to Part(c), From 'fable 5-3, the average travel speed is approximately 30 mph. General methodology for capacity analysis for signalized intersection 'The capacity of a signalized intersection is highly dependent on the type of signal control being used. A wide variety of equipment and control schemes may be used for such intersections. The capacity of a signalized intersection is therefore far more variable than that of other types of facilities, where capacity depends primarily on the physical geometry of the roadway. In intersection analysis, the concepts of capacity and level of service are not as strongly correlated as they are for other types of facilities. The Highway Capacity Manual (4) therefore recommends that separate analyses be used to determine the capacity and level of service for a signalized intersection. The capacity of signalized intersections should be defined for each ap proach. 1 Intersection approach capacity is the maximum rate of How which may pass through the intersection by that approach under prevailing roadway, traffic, and signalization conditions. 'To account for peaking, the rate of flow is usually measured or projected for a 15-min period, and capacity is expressed in vehicles per hour (4). Operational analysis of a signalized intersection requires detailed infor mation on the roadway, the signal system, and the traffic at the intersection. Required information on the roadway includes approach grades, the number and width of lanes, parking conditions, and the existence and lengths of exclusive turning lanes, Complete information is needed on signalization including the phase plan, cycle length, green times, type of signal operation (actuated or pretimed), and existence of push-button pedestrian-actuated phases. (These and other traffic control concepts are discussed in more detail in Chapter 12.) Capacity analyses of signalized intersections require detailed information on traffic conditions including 1. Traffic volumes for each movement, on each approach. 2. Percentage of heavy vehicles. 3. Volume and pattern of pedestrian traffic. 4. Rate of parking maneuvers within the vicinity of the intersection. 5. Number of local buses picking up or discharging passengers at the intersection. In addition, information is needed on the shape of the arrival curve distribution and its relationship to the signal operation. This factor describes the platooning effect in arriving flows. It affects the average stopped delay of vehicles passing through the intersection, which defines the level of service. The Highway Capacity Manual {4) categorizes arrival distributions by defining five arrival types, defined as follows. Type 1 is the worst platoon condition, defined as a dense platoon arriving at the intersection at the beginning of the red phase. Type2 is a generally unfavorable platoon condition, which may be a dense platoon 1It may also be desirable to evaluate separately the capacity of designated lanes or lane groups such as those serving a particular movement, or set of movements.

Traffic Flow Characterist ics 121

arriving during the middle of the red platoon arriving throughout the red phase.

phase or a

dispersed

Type 3 refers to totally random arrivals that are widely dispersed through out the red and green phases. Type 4 is a moderately favorable platoon condition, defined as a dense platoon arriving during the middle of the green phase or a dispersed platoon arriving throughout the green phase. Type 5 is the most favorable platoon condition, defined as a dense platoon arriving at the beginning of the green phase. The Highway Capacity Manual (4) relates the arrival types to a platoon ratio, which is defined by Rp = PVGIPTG (5-10) where Rp = platoon ratio PVG = percentage of all vehicles in the movement arriving during the green phase PTG ~ percentage of the cycle that is green for the movement 'The relationship between arrival type and the platoon ratio is shown in 'fable 5-7. The capacity of signalized intersections is based on the concept of a saturation flow rale. The Highway Capacity Manual (4) defines saturation flow rate as the maximum rate of flow that can pass through an intersection approach or lane group under prevailing roadway and traffic conditions, assuming that the approach or lane group has 100 percent of real time available as effective green time. Saturation flow rate is expressed in units of vehicles per hour of effective green time. TABLE 5-7

RELATIONSHIP BETWEEN ARRIVAL TYPE AND PLATOON RATIO Arrival Type

Range of Platoon Ratio, Rp

1

0.00 to 0.50

2 3 4

0,51 to 0.85 0.86 to 1.15 1.16 to 1.50

5

> 1.51

Highway Capacity Manual. Transportation Research Board Special Report No, 209 (1985). SOURCE:

'The capacity of a given lane group or approach may be calculated by the equation c

. = s. x (giC),

(5-11)

where c; — capacity of lane group or approach i (vehicles/hr) ,v, - saturation flow rate for lane group or approach i (vehicle/hr of green)

122 TRAFFIC CHARACTERISTICS

(g/C); = green ratio for lane or approach i The computation of the saturation flow rate begins with the selection of an “ideal” saturation flow rate, usually taken to be 1800 passenger cars per hour of green Lime per lane. This value is then adjusted to account for the various prevailing conditions. The equation for estimating saturation flow rate is S = Nfnftt vfjpfbbfjii rfi. r

where s — saturation flow rate for tine subject lane group, expressed as a total for all lanes in the lane group under prevailing conditions (vehicles/ hr green) S„ ~ ideal saturation flow rate per lane, usually 1800 passenger ears per hour of green time per lane N = number of lanes in the lane group f~ ( , = adjustment factor for lane width; 12-ft lanes are standard; given in 'Fable 5-8 f / / v = adjustment factor for heavy vehicles in the traffic stream, given in 'Fable 59 / ff = adjustment Factor for approach grade, given in Table 5-10 f f , = adjustment factor for existence of a parking lane adjacent to the lane group and parking activity in that lane, given in Table 5-11 ft>b = adjustment factor tor blocking effect of local buses stopping within the intersection area, given in Table 5-12 /„ = adjustment factor for area type, given in Table 5-13 fliT " adjustment factor for right turns in the lane group fLT = adjustment factor for left turns in the lane group Adjustment factors for turning movements are not included here but may be found in Ref. 4. The level of service for signalized intersections is defined in terms of delay. Specifically, level of service is based on the average stopped delay per vehicle for a 15-min. analysis period, as specified in Table 5-14.

\BLE 5-8 DJUSTMENT FACTOR FOR LANE WIDTH me Width, ft

9

8

10

11

0,93

0.97

12 13

14

15

>16

1.07

1.10

Use 2 lanes

me Width Factor, fu,

0.87

0,90

1.00 1.03

)UROE: Highway Capacity Manual. Transportation Research Board Special Report No. 209 (1985).

ABLE 5-9 DJUSTMENT FACTOR FOR HEAVY VEHICLES ;rcent Heavy Vehicles, %HV

0

2

4

6

8 10

15

1.00

0.99

0.98

0.97

0.96 0.95

0.93

20

25 30

eavy Vehicle Factor / HV

0.91

>URCE: Highway Capacity Manual. Transportation Research Board Special Report No. 209 (1985).

\BLE 5-10 DJUSTMENT FACTOR FOR GRADE

0.89 0.87

Traffic Flow Characterist ics 123

Downhill “6 4-6

rade, % rade, Factor, fg

1.03 0.97

-4

1,02

LevelUphill 4-2 4-4

-20

1.01

1.00

0.99

0.98

hjrce: Highway Capacity Manual. Transportation Research Board Special Report No. 209 (1985).

\BLE 5-11 DJUSTMENT FACTOR FOR PARKING

Number of Parking Maneuvers per Hour, Nm ’ Group 1 2 3

Parking

0

10

20

30

40

1.00 1.00 1.00

0(90 0.95 0.97

0.85 0,92 0.95

0.80 0.89 0.93

0.75 0.87 0.91

0.70 0.85 0.89

>URCE: Highway Capacity Manual. Transportation Research Board Special Report No. 209 985).

Traffic Flow Characterist ics 124

TABLE 5-12

ADJUSTMENT FACTOR FOR BUS BLOCKAGE Number of Buses Stopping per Hour,

Number of Lanes in Lane Croup

0

10

1 9 3

LOO 1.00 1.00

0.96 0.98 0.99

30 40

20 0.92 0.96 0.97

0.88 0.83 0.94 0.92 0.96 0.94

SotJRc.r.: Highway Capacity Manual. Transportation Research Board Special Report No, 209 (1989)-"

TABLE 5-13

TABLE 5-14

ADJUSTMENT FACTOR FOR AREA TYPE

LEVEL OF SERVICE CRITERIA FOR SIGNALIZED INTERSECTIONS

Type of Area Central business district All other areas

Factor f«

Stopped Delay per Vehicle (sec)

Level of Service A

0.90 1.00

Highway Capacity Manual.'Ynmsportaiion Research Board Special Report No. 209 (1989).

<5.0

B C

5.1 to 15.0 15.1 to 25.0

I)

25.1 to 40.0 40.1 to 60,0 >60.0

E F

The average stopped delay per vehicle can be estimated by the following equation, assuming a random pattern of arrivals for approaching vehicles. ;i - gic) 2 0.38C

+ 173 X

d “ (g/C) (X)]

+ V(X - l)2 T (16X/c)

(x- r

(5-13)

where d = average stopped delay per vehicle for the lane group (sec/vehicle) C = cycle length (sec) g/C = green ratio for the lane group; ratio of effective green time to cycle length X = vie ratio for the lane group c = capacity of the lane group

Where the arrivals are not random, the delay obtained from Eq. 5-13 can be multiplied by an adjustment factor, which is a function of arrival type, vie ratio, and type of signalization. Such factors are not included here but can be found in Ref. 4,

The Highway Accident Problem 125

EXAMPLE 5-4. Capacity of a Signalized Intersection. (a) Determine the ca pacity of the south approach lanes for a signalized intersection given the fo 1 lo w i n g co n d i ti o n s: 2 approach lanes, 11 ft wide 10 percent heavy vehicles 2 percent downgrade along the south approach location in the central business district no buses stopping in the intersection and no parking permitted type 3 (random) arrivals through traffic only cycle length = 60 sec green ratio ~ 0.45 (b) What is the level of service for a flow rate of 1000 vehicles/hr. assuming equal lane utilization for the two lanes? Solution to Part a. By Eq. 5-12, and using Tables 5-8through 5-13, s = 1800 x 2 x 0.97 x 0.95 x 1.01 x 0.90 .v = 3015 vehicles/hr of green By Eq. 5-11, ct = 3015 x 0.45 = 1357 vehicles/hr

(0.74 - 1) +

Solution to Part b. For random arrivals, Eq. 5-13 the average stopped delay per vehicle. [1 - 0.45] d = 0.38(60) ................................. - + 173(0.74) 2 [1 - (0.45)(0.74)]

can

be used to estimate

V(0.74 - if + (16 x 0.74)/1357 d ~ 11.9 sec per vehicle From Table 5-14, the approach operates at level of service B,

THE HIGHWAY ACCIDENT PROBLEM Since 1900, more than 2 million deaths have resulted from motor vehicle accidents, far exceeding the number of Americans killed in all of the nation’s wars combined. In 1983 alone, highway accidents in the United States pro duced 44,600 deaths, 1.9 million disabling injuries, and economic losses of more than 43.3 billion (9). Traffic accidents are the fourth leading cause of death in the country, exceeded only by heart disease, cancer, and stroke. For persons between the ages of 1 and 24, motor

126 TRAFFIC CHARACTERISTICS

vehicle accidents are the leading cause of death, Despite the long history and pervasiveness of the problem, the nature and causes of traffic accidents are not well understood. While there are differences

The Highway Accident Problem 127

of opinion among traffic safety professionals concerning why crashes occur, there are greater differences concerning the programs of action required to reduce highway losses.

5-7 Accident loss factors It is helpful to think of an accident as an event comprised of nine parts, called crash factors. One may visualize an accident in three phases: precrash, at-crash, and postcrash. Within each phase, one or more human, vehicular, and environ mental factors may contribute to the initiation of the crash or alter its conse quences. Examples of the nine classes of loss factors are shown in Table 5-15, These factors may be arranged in the form of a nine cell matrix. Counter measures designed to reduce highway deaths and injuries may be focused on any one or a combination of the cells that comprise the loss factor matrix. Precrash countermeasures are concerned with the prevention of accidents. At-crash countermeasures attempt to reduce injuries by controlling the energy of crashes. Postcrash programs are designed to limit the losses by improving first-aid and other emergency procedures. This part of the chapter is concerned primarily with precrash factors, that is, those aspects of the driver, the vehicle, and the roadway environment that explain the occurrence of the accident event.

5-8 The nature of vehicular crashes One of the most striking features of scientific accident causation data is the wide variety of human, vehicular, and roadway factors that contribute to vehicular crashes. Many accidents—perhaps one-third to one-half of all crashes—are uncomplicated events that can be explained by the presence of a single human, vehicular, or environmental factor. These factors range from simple lapse of driver attention to the relatively rare case of a driver who uses the automobile as an instrument of suicide. TABLE 5-15

EXAMPLES OF MINE CLASSES OF ACCIDENT LOSS FACTORS Designation Precrash Human Vehicle Environment At-crash H uman Vehicle Environment

Example

Driver fell asleep Brake failure Slippery roadway surface Seat belts improperly worn Structural weakness of side of vehicle Unyielding signpost near pavement

Posterash Human Vehicle

Bystanders took improper first-aid action Vehicle not. equipped with a fire extinguisher

Environment

Emergency telephone not available

Many crashes, however, are complex events that, are triggered by two or more factors. For example, consider a crash involving a driver driving a vehicle with

128 TRAFFIC CHARACTERISTICS

worn tires at an excessive speed along a wet and slippery roadway. The combined presence of these factors could cause a crash, Removal of any of the factors—the excessive speed, the slippery roadway, or the worn tires—might have prevented the crash from occurring. For many years, traffic safety specialists have maintained that 90 percent of all accidents are due to improper driving. It appears that this conclusion, which is based on analyses of police accident reports, oversimplifies a complex problem and exaggerates the role of driver behavior. Nevertheless, multidisci plinary research has indicated that human factors are die most prevalent type of contributing factors. It is believed, however, that not more than half of traffic accidents can be attributed to human factors alone. Research has shown that, a substantial percentage of crashes results from a variet y of driver malfunctions and conditions. Driver inattention or distraction, excessive speed, and violation of other safe driving practices appear to be recurring contributing factors. Many crashes can be explained by some form of driver impairment such as fatigue, emotional stress, physical illness, or failure to wear needed corrective lenses. By far the most prevalent form of driver impairment is alcohol intoxication. Vehicular factors that contribute to crashes are more commonly classified as vehicular conditions (e.g., slick tires) rather than malfunctions or cata strophic failures due to poos' design. Defective brakes (especially gross brake failure) and tires (especially inadequate tread depth and underin Ration) are frequently cited as contributors to crashes. Vehicular factors are rarely solely responsible for an accident but. usually occur jointly with human and/or en- viromental factors. Environmental factors commonly interact, with some other factor (human or vehicle) to produce an accident. Although a crash may result from a natural disaster or from a malfunction in die highway or its appurtenances, these events are extremely rare, Typical examples of environmental factors that contribute to crashes are wet. roadways, missing or improper traffic control devices, and poor geometric design.

5-9 Conceptualization of an accident Multidisciplinary research lias shown that, traffic accidents are caused by a diversity of human, vehicular, and environmental factors that often interact in a complex way to trigger the initiation of the event. A fairly wide tolerance is permissible (not. accident causative) in any one component of the human/ machine/environment system. Even a “drunk” may successfully manipulate an automobile under certain conditions, such as down a wide street with which lie is familiar and on which there are no other vehicles or roadside hazards. Conversely, a skilled driver may avoid an unexpected hazard presented either by vehicle failure or by the environment. Blumenthal (10) has conceptualized the variability in tolerences in terms of driver performance and system de mands, both of which fluctuate unpredictably over a period of time. As Figure

'Flie Highway Accideni Problem 129 5-11 illustrates, accidents occur at some point in time when the system demands exceed the performance capability of the driver.

5-10 Current accident trends and concerns In recent years, significant advances have been made in improving highways for safety and in designing more crashworthy vehicles. Numerous and expen sive programs aimed at improving the driving function have been sponsored by the federal government and implemented by the state governments. Strong evidence exists that these initiatives have yielded positive results. This is best demonstrated by the fatality rate, which fell to an all-time low of 2.58 fatalities per 100 million vehicle-miles of travel in 1983, approximately half of the rate for the mid-1960s. Nevertheless, vehicular accidents remain one of the nation’s most persistent and troublesome public health problems. By the mid-1980s, traffic safety specialists focused attention on four areas of concern: (1) the influence of alcohol; (2) the nonuse of occupant restraints; (3) crash losses from the growing population of large trucks; and (4) the effects of vehicular crashes on the elderly (11). Researchers have consistently reported that alcohol contributes to more than half of fatal crashes. A nationwide survey in 1983 (12) revealed that 57 percent of all fatally injured drivers had been drinking and 46 percent were legally intoxicated. The incidence of alcohol involvement in fatal crashes tends to be greatest in late night and early morning accidents, when 80 to 90 percent of all fatally injured drivers are reported to have been drinking (12). It is estimated that alcohol is involved in 29 percent of injury accidents and about 11 percent of all accidents (11). Under strong pressure from citizens groups and the general public, legislatures in many states have increased the penalties for driving under the influence of alcohol. Scientific research has clearly established that vehicle occupants who are

FIGURE 5-11 A concept of a traffic accident.

r e s t r a i n e d b y . s a fe t y b e l t s a r e fa r l e s s l i ke l y t o b e i n j u r e d t h a n t h o s e wh o a r e n o t r e s t r a i n e d. Yet , d e s p i t e n u me r o u s “b u c kl e u p ” c a mp a i gn s b y p u b l i c

130

TRAFFIC CHARACTERISTICS

a ge n c i e s , a u t o m o b i l e m a n u fa c t u r e r s , a n d p r i va t e gr o u p s , fe w d r i ve r s we a r s a fe t y b e l t s . R e s e a r c h i n d i c a t e s t h a t a b o u t 8 2 p e r c e n t o f p e o p l e i n ca r s i n vo l ve d i n c r a s h e s we r e n o t we a r i n g s a fe t y b e l t s (11). S i gn i fi c a n t d e c l i n e s i n c r a s h - r e l a t e d i n j u r i e s a n d d e a t h s a r e l i ke l y t o r e s u l t fr o m gr e a t e r u s e o f a u t o m a t i c r e s t r a i n t s ys t e m s . 'T h e s e s ys t e ms a r e o f t wo t yp e s : a u t o ma t i c b e l t s , wh i c h m o ve i n t o p o s i t i o n wh e n t he d o o r i s c l o s e d ; a n d a i r b a gs , wh i c h i n fl a t e i n a s e r i o u s c r a s h t o c u s h i o n t h e c o l l i s i o n o f o cc u p a n t s wi t h t h e ve h i c l e ’s i n t e r i o r. F o r m a n y ye a r s , r e s e a r c h e r s h a ve u n d e r s t o o d t h e r e la t i o n s h i p b e t we e n ve h i c l e s i z e a n d i n j u r y s e ve r i t y. C le a r e vi d e n c e e xi s t s t h a t wh e n t wo ve h i c l e s c o l l i d e , o c c u p a n t s o f t h e l a rge r ve h i c l e ar e fa r l e s s l i ke l y t o b e s e r i o u s l y i n j u r e d o r ki l l e d t h a n t h o s e t r a ve l i n g i n t h e s ma l l e r ve h i c l e . Th e h a z a r d s a s s o c i a t e d wi t h ve h i c l e s i z e a r e mo s t p r o mi n e n t i n c o l l i s i o n s t h a t i n vo l ve a l a rge t r u c k a n d a n a u t o mo b i l e . In s u c h c r a s h e s , a u t o mo b i l e o c c u p a n t s a r e 3 0 t i m e s a s l i ke l y t o b e ki l l e d a s oc c u p a n t s o f t h e t r u c k. D e r e gu l a t i o n o f t h e t r uc ki n g i n d u s t r y an d t h e r e l a xa t i o n o f r e s t r i c t i o n s o n t r u c k we i g h t a n d s i z e a r e l i ke l y t o i n c r ea s e a c c i d e n t l o s s e s. H i gh wa y a n d t r a ffi c e n gi n e e r s fa c e t h e d i ffi c u l t c h a l l e n ge o f p r o vi d i n g a s a fe d r i vi n g e n vi r o n m e n t fo r d r i ve r s o f a n e ve r -wi d e n i n g a r r a y o f ve h i c l e t yp e s a n d sizes. P e o p l e o ve r t h e a ge o f 6 5 r e p r e s e n t a s ma l l p r o p o r t i o n o f t h o s e wh o a r e i n vo l ve d i n c r a s h e s ; h o we ve r, wh e n t h e y a r e i n vo l ve d , t h e y a re a t gr e a t e r r i s k o f d e a t h o r s e r i o u s , p r o l o n ge d i n j u r y t h a n a r e yo u n g p e o p l e ( / / ) . O l d e r d r i ve r s a re m o r e l i ke l y t o b e d r i vi n g t h e s t r u c k r a t h e r t h a n t h e s t r i ki n g ve h i c l e i n m u l t i p l e - ve h i c l e a c c i de n t s a n d t e n d t o b e i n vo l ve d i n fe we r s i n gl e - ve h i c l e a c c i d e n t s t h a n yo u n g e r d r i ve r s . E ffo r t s t o d e c r e a s e c r a s h - r e l a t e d i n j u r i e s a n d d e a t h s a mo n g t h e el d e r l y s h o u l d t h e r e fo r e b e d i r e c t e d t o p r o vi d i n g b e t t e r p r o t e c t i o n fo r t h e m i n t h e c r a s h an d p r o vi d i n g i m p r o ve d e m e r ge n c y m e d i c a l s e r vi c e s a n d h o s p i t a l c a r e d u r i n g t h e p o s t c r a s h p e r i o d.

PROBLEMS 5-1 Three cars travel over a 200-ft section of highway at constant speeds of 30,35, and 40 ft/sec. Compute the time-mean and space-mean speeds for this condition. 5-2* Four cars travel over a 60-m section of highway at constant speeds of 18, 20 and 22 m/sec. Compute the lime-mean and space-mean speeds for this condition. 5-3 For die conditions described in Problem 5-1, estimate the variance about the space-mean period. 5-4* For the conditions described in Problem 5-2, estimate the variance about the space-mean speed in meters per sec. 5-5 The estimated future average daily traffic lor a rural highway is 9500. Assume that the relationship between peak hourly flows and ADT is as shown in Figure 5-2. Estimate the design hourly How volume. What would be the effect of using the 10th highest hour for design purposes? The 50th highest hour? 5-6 Arrivals at a parking lot are assumed to follow the Poisson distribution. The average arrival rate is 3,0 per minute. What is the probability that during a given minute no cars will arrive? What percentage ol the time will more than three arrive?

References 131 5-7 A street has an hourly volume of 300 vehicles. A pedestrian requires a gap of at least 10 sec to cross. Assuming headways can be described by a negative exponential distribution, what is the probability that the pedestrian will have to wait to cross? 5-8 Compute the slope of the volume—density curve shown in Fig. 5-6 at points A, B, and C. What are the units of the slope? Discuss the meaning of the slope of this curve. (See Ref. 5.) 5-9 Compute the density corresponding to the maximum volume for the q~k curve shown in Fig. 5-7. 510 Estimate the service flow rate for level of service B for a six-lane freeway (three lanes in each direction) with 12-ft lanes and obstructions 6 ft from the edge of the pavement on one side only. The section is to accommodate 10 percent heavy trucks, 5 percent buses, and no recreational vehicles. Assume the adjustment factor for the character of the traffic stream,/ p , is 0.95. The design speed is 75 mph and the section is level. 511 Estimate the capacity of the freeway segment described in Problem 5-10. 512 Estimate the capacity of the approach lanes of a signalized intersection given the following conditions: two approach lanes, 10 ft wide

f 5 parking manuevers per hour type

12 percent heavy vehicles flat

3 (random) arrivals through traffic

grades

only cycle length = 65 sec green

location in central business district

ratio — 0.50

20 buses stopping per hour 513 Determine the level of service for a How rate of' 1100 vehicles/hr for the ap proach lanes described in Problem 5-12. Assume equal lane utilization for the two lanes, 514 Consult with the State Office of Highway Safety and prepare a report on the approximate annual costs of the following types of safety countermeasures: (a) Driver education. (b) Motor vehicle inspection. (c) Traffic enforcement.

REFERENCES 1.

Wardrop, J. G. Some Theoretical Aspects of Road Traffic Research. Proceedings of Civil Engineers, Pi. 2, Vol. I, pp. 325-362 (1952). 2. Oppenlander, Joseph C. Multivariate Analysis of Vehicular Speeds. Highway Research Record No. 7.5, p. 63 (1963). 3. Guide for Traffic Volume Counting Manual. Bureau of Public Roads, U.S. Department of Commerce, Washington, D.C. (1965). 4. Highway Capacity Manual. Transportation Research Board Special Report No. 209 (1985). 5. P ms son and Other Distributions in Traffic. Eno Foundation for Transportation, Saugatuck, Conn, (1971). of the Institution

TRAFFIC CHARACTERISTICS 6.

Traffic Flow Theory, A Monograph. Transportation Research Board Special Report No. 165

(1975),

7. Greenshields, B. D. A. Study of Traffic Capacity. Proceedings of the Highway Research Board Vol. 14, pp. 448-477 (1934), 8. Highway Capacity Manual. Bureau of Public Roads, U.S. Department of Commerce, Washington, D.C. (1950).

9. 10.

Accident Facts, 1984 Edition. National Safety Council, Chicago, III. (1984).

Blumeiuhal, M. Problem Definition: The Driving Task in the System Context. Pre sented at the American Psychological Association, San Francisco (1968). 11. National Accident Sampling System 1983. National Highway Traffic Safety Administra tion, Washington, D.C. (1985). 12. Fatal Accident Reporting System 1983. National Highway Traffic Safely Administration, Washington, D.C. (1984)/

--------------------------------------------------chapter six

TRANSPORTATION PLANNING P l a n n i n g i s a c o n s c i o u s, d e l i b e r a t e p r o c e s s o r ac t i vi t y t h a t i s d i r e c t e d t o wa r d t h e a c h i e ve m e n t o f s t a t e o r c o m mu n i t y go a l s (1). It mu s t h e c a p a b le o f d e a l i n g wi t h c o m p l e x s u b j e c t s an d e va l u a t i n g a l t e r n a t i ve s o l u t i o n s o r c o u r s e s o f a c t i o n. Me a n i n g fu l p l a n n i n g i s b a s e d o n t h e a s s u mp t i o n t h a t t h e p o we r e xi s t s t o i m p l e m e n t t h e p l a n s t h a t , a r e d e ve l o p e d . T h e c o n s t r u c t i o n o f t r a n s p o r t a t i o n s ys t e m s l i a s a p r o fo u n d a n d fa rr e a c h i n g i m p a c t o n l a n d u s e a n d t h e s o c ia l a n d e c o n o mi c we l l - b e i n g o f c i t i z e n s. F o r t h i s r e a s o n , t r a n s p o r t a t i o n p l a n n i n g i s a ma j o r c o mp o n e n t o f s t a t e a n d l oc a l p l a n n i n g a c t i vi t i e s , In t he U n i t e d S t a t e s , t h e p l a n n i n g o f h i gh wa y s ys t e m s t e n d s t o b e t h e d o mi n a n t e le me n t i n mu l t i mo d a l t r a n s p o r t a t i o n p l a n n i n g. P r i o r t o 1 9 3 0, t h e p r i ma r y o b j e c t i ve o f h i gh wa y a ge n c i e s wa s t o d e ve l o p a s ys t e m o f p a ve d r u ra l r o a d s , Th e r e wa s l i t t l e e mp h a s i s o n p l a n n i n g, a s t h e h i gh wa y d e p a r t me n t s c o n c e n t r a t e d o n ge t t i n g r o a d u s e r s “ o u t o f t h e m u d / ’ S h a r p i n c r ea s e s i n mo t o r - ve h i c l e r e gi s t r a t i o n s a n d t r a ve l d u r i n g t h e e a r l y 1 9 3 0 s ma d e i t ap p a r e n t t h a t t h e h i gh wa y s ys t e m wo u l d s o o n b e c o m e i n a de q u a t e fo r fu t u r e n e e d s . F ac t u a l i n fo r ma t i o n wo u l d b e r e q u i r e d i f s o u n d p o l i c i e s an d d e c i s i o n s we r e t o b e ma d e r e ga r d i n g t h e d e ve l o p m e n t o f a n a d e q u a t e a n d e ffi c i e n t n a t i o n a l s ys t e m o f h i gh wa ys . A n a c t o f C o n gr e s s a d o p te d i n 1 9 3 4 a n d kn o wn a s t h e H a yd e n C a r t wr i gh t Ac t p r o vi d e d t he i mp e t u s fo r a l a rge n u mb e r o f h i gh wa y p l a n n i n g s u r ve ys s t a r t i n g i n 1 9 3 5. Th e s u r ve ys we r e d e s i gn e d t o d e t e r mi n e t i r e c o n d i t i o n o f e xi s t i n g fa c i l i t i e s , t h e vo l u me a n d n a t u r e o f t r a ffi c u s i n g t h e h i gh wa y s ys t e m , t h e u s e a n d l i fe e xp e c t a n c y o f r o a d s c o mp r i s i n g t h e s ys t e m , a n d fu t u r e h i gh wa y n e e d s .

T h e H a yd e n — C a r t wr i g h t Ac t a u t h o r i z e d t h e e xp e n d i t u r e o f fu n d s n o t t o e xc e e d 1 . 5 p e r c e n t o f t h e fe d e r a l - ai d a p p o r t i o n me n t t o a n y s t a t e fo r t h e m a ki n g o f s u r ve ys , p l a n s , a n d e n gi n e e r i n g i n ve s t i ga t i o n s o f p r o j e c t s fo r fu t u r e c o n s t r u c t i o n. B y 1 9 4 0 , p r a c t i ca l l y al l s t a t e h i gh wa y d e p a r t m e n t s , i n c o o p e r a t i o n wi t h t h e B u r e a u o f P ub l i c R o a d s, we r e d o i n g s u c h s u r ve ys . At t h e t i m e o f t h e p a s sa ge o f t h e H a yd e n — C a r t wr i gh t . Ac t t h e p h i l o s o p h y o f t h e F e d e r a l - A i d H i gh wa y P r o gr a m wa s t o a s s i s t t he r u r a l a r e a s, b u t wi t h t he i n c r e a s e i n mo t . o r- ve h i d e r e gi s t r a t i o n an d t r a ffi c vo l u m e s , s i gn s o f d i s t r e s s s o o n b e c a me a p p a r e n t i n u r b a n a n d s u b u r b a n a r e a s. Th u s , i t wa s l o gi c a l t ha t p l a n n i n g a c t i vi t i e s s h o u l d h e e xt e n d e d t o t h e s e a re a s , Wit h t he p a s s a ge o f t h e F e d e r a l - A i d Ac t o f 1 9 4 4 , fu n d s b e c a m e a va i l a b l e fo r fe d e r a l - a i d h i gh wa y co n s t r u c t i o n i n u r b a n a r e a s. T h e F e d e ra l - A i d H i gh wa y Ac t o f 1 9 6 2 fu r t h e r d e l i n e d t h e r e q u i r e m e n t s fo r p l a n n i n g p r o c e s s e s i n u r b a n a r e a s wi t h a p o p u l a t i o n o ve r 5 0, 0 0 0 , t o b e

132 T R A F F I C C H A R A C T E R I S T I C S 6. Traffic T'lou> Theory, A Monograph- Transportation Research Board Special Report No. 165 (1975), 7. Greenshields, B. D. A. Study of Traffic Capacity. Proceedings of the Highway Research Board Vol. 14, pp. 448-477 (1934). 8. Highway Rapacity Manual. Bureau of Public Roads, U.S. Department of Commerce, Washington, D.C. (1950). 9. Accident Facts, 1984 Edition. National Safety Council, Chicago, 111. (1984). 10. Blumenthai, M. Problem Definition: The Driving Task in the System Context. Pre sented at the American Psychological Association, San Francisco (1968). 11. National Accident Sampling System 1983. National Highway Traffic Safety Administra tion, Washington, D.C. (1985). 12. Fatal Accident Reporting System 1983. National Highway Traffic Safely Administration, Washington, D.C. (1984)/

---------------------------------------------------chapter six

TRANSPORTATION PLANNING P l a n n i n g i s a c o n s c i o u s, de l i b e r a t e p r o c e s s o r ac t i vi t y t h a t i s d i r e c t e d t o wa r d t h e a c h i e ve m e n t o f s t a t e o r c o mmu n i t y go a l s (1). It mu s t b e c a p a b l e o f d e a l i n g wi t h c o m p l e x s u b j e c t s an d e va l u a t i n g a l t e r n a t i ve s o l u t i o n s o r c o u r s e s o f a c t i o n . Me a n i n g fu l p l a n n i n g i s b a s e d o n t h e a s s u mp t i o n t h a t t h e p o we r e xi s t s t o i m p l e m e n t t h e p la n s t h a t a r e d e ve l o p e d . T h e c o n s t r uc t i o n o f t ra n s p o r t a t i o n s ys t e ms h a s a p r o fo u n d a n d fa r r e a c h i n g i m p a c t o n l a n d u s e a n d t h e s o c ia l a n d e c o n o mi c we l l - b e i n g o f c i t i z e n s . F o r t h i s r e a s o n , t r a n s p o r t a t i o n p l a n n i n g i s a ma j o r c o mp o n e n t o f s t a t e a n d l o c a l p l a n n i n g a c t i vi t i e s . In t h e U n i t e d S t a t e s, t h e p l a n n i n g o f h i gh wa y s ys t e m s l e n d s t o b e t h e d o mi n a n t e le me n t i n mu l t i mo d a l t r a n s p o r t a t i o n p l a n n i n g. P ri o r t o 1 9 3 0 , t h e p r i ma r y o b j e c t i ve o f h i gh wa y a ge n c i e s wa s t o d e ve l o p a s ys t e m o f p a ve d r u ra l r o a d s, Th e r e wa s l i t t l e e mp h a s i s o n p l a n n i n g, a s t h e h i gh wa y de p a r t me n t s c o n c e n t r a t e d o n ge t t i n g r o a d u s e r s “ o u t . o f d i e m u d . ” S h a r p i n c r e a se s i n mo t o r-ve h i c l e r e gi s t r a t i o n s a n d t r a ve l d u r i n g t h e e a r l y 1 9 3 0 s ma d e i t a p p a r e n t t h a t t h e h i gh wa y s ys t e m wo u l d s o o n b e c o m e i n a de q u a t e fo r fu t u r e n e e d s . F a c t u a l i n fo r ma t i o n wo u l d h e r e q u i r e d i f s o u n d p o l i c i e s a n d d e c i s i o n s we r e t o be ma d e r e ga r d i n g t h e d e ve l o p m e n t o f a n a de q u a t e a n d e ffi c i e n t n a t i o n a l s ys t e m o f h i gh wa ys . A n a c t o f C o n gr e s s a d o p t e d i n 1 9 3 4 a n d kn o wn a s t h e H a yd e n C a r t wr i g h t Ac t p r o vi d e d t he i mp e t u s fo r a l a rge n u mb e r o f h i gh wa y p l a n n i n g s u r ve ys s t a r t i n g i n 1 9 3 5 . Th e s u r ve ys we r e d e s i gn e d t o d e t e r mi n e t h e c o n d i t i o n o f e xi s t i n g fa c i l i t i e s , t h e vo l u me a n d n a t u r e o f t r a ffi c u s i n g t h e h i gh wa y s ys t e m , t h e u s e a n d l i fe e xp e c t a n c y o f r o a d s c o mp r i s i n g t h e s ys t e m , a n d f u t u r e h i gh wa y n e e d s . T h e H a yd e n — C a r t wr i g h t Ac t a u t h o r i z e d t h e e xp e n d i t u r e o f fu n d s n o t t o e xc e e d 1. 5 p e r c e n t o f t h e fe d e r a l - a i d a p p o r t i o n me n t t o a n y s t a t e fo r

t h e m a ki n g o f 's u r ve ys , p l a n s, an d e n gi n e e r i n g i n ve s t i ga t i o n s o f p r o j e c t s l o r fu t u r e c o n s t r u c t i o n . B y 1 9 4 0, p r a c t i c a l l y a l l s t a t e h i gh wa y d e p a r t me n t s , i n c o o p e r a t i o n wi t h t h e B u r e a u o f P u b l i c R o a d s , we r e d o i n g s u c h s u r ve ys . At t h e t i m e o f t h e p a s s a ge o f t h e H a yd e n — C a r t wr i gh t . Ac t t h e p h i l o s o p h y o f t h e F e d e r a l - A i d H i gh wa y P ro gr a m wa s t o a s s i s t t h e r u r a l a r e a s, b u t wi t h t h e i n c r e a s e i n m o t . o r - ve h i c l e r e gi s t r a t i o n a n d t r a ffi c vo l u me s , s i gn s o f d i s t r e s s s o o n b e c a m e a p p a r e n t i n u r b a n a n d s u b u r b a n a r e a s . Th u s , i t wa s l o gi c a l t h a t p l a n n i n g a c t i vi t i e s s h o u l d b e e xt e n d e d t o t h e s e a r ea s . Wit h t h e p a s s a ge o f t h e F e d e r a l - A i d Ac t o f 1 9 4 4, fu n d s b e c a me a va i l a b l e fo r fe d e r a l - a i d h i gh wa y c o n s t r u c t i o n i n u r b a n a r e a s . T h e F e d e r a l - A i d H i gh wa y Ac t o f 1 9 6 2 fu r t h e r d e fi n e d t h e r e q u i r e m e n t s fo r p l a n n i n g p r o c e s s e s i n u r b a n a r e a s wi t h a p o p u l a t i o n o ve r 5 0 , 0 0 0, t o h e e ffe c t i ve J u l y 1 , 1 9 6 5. Th e l a w re q u i r e d t h e e s t a b l i s h me n t o f a “ c o o p e r a t i ve , c o m p r e h e n s i ve , a n d co n t i n u i n g” t r a n s p o r t a t i o n p l a n n i n g p r o c e s s i n e a c h o f t h e s e a r e a s as a p r e r e q u i s i t e fo r fe d e r a l a i d. B y t he d e a d l i n e , n e a r l y a l l o f t h e mo r e t h a n 2 0 0 s u c h a r ea s i n t h e c o u n t r y h a d met. die requirement. B y t h e m i d - 1 9 7 0 s , m u l t i mo d a l t r a n s p o r t a t i o n p l a n n i n g h a d b e c o me a ke y a c t i vi t y o f p r a c t i c a l l y a l l s t a l e h i gh wa y o r t r a n s p o r t a t i o n a ge n c i e s a n d o f m o s t u r b a n p l a n n i n g a ge n c i e s . In t h i s c h a p t e r, t h e p l a n n i n g p o l i c i e s a n d p r o c e d u r e s e m p l o ye d b y s u c h a ge n c i e s a r e de s c r i b e d .

6-1 Definition A s t h e t e r m s u gge s t s , t r a n s p o r ta t i o n p l a n n i n g i s c o n c e r n e d wi t h t he d e ve l o p m e n t . o f a t r a n s p o r t a t i o n p l a n fo r a n u r b a n a r e a o r fo r a n e n t i r e s t a t e . Th i s i n vo l ve s ge n e r a t i n g an d c o mp a r i n g a l t e r n a t i ve p l a n s, e va l u a t i n g t h e s o c i a l , e c o n o m i c , a n d e n vi r o n me n t a l i mp a c t s o f p r o p o s e d t ra n s p o r t a t i o n a c t i o n s , a n d, wi t h a p p r o p r i a t e p a r t i c i p a t i o n o f c i t iz e n s , p o l i t i c a l r e p r e s e n t a t i ve s , a n d p u b l i c a ge n c i e s , s e l e c t i n g t h e p r e fe r r e d p l a n . 'Tra n s p o r t a t i o n p l a n n i n g s h o u l d b e vi e we d a s a c o n t i n u i n g p r o ce s s t b a t t a ke s i n t o a c c o u n t c h a n ge s i n t he n e e d s a n d wi s h e s o f t h e c i t i z e n s a n d t h e i r p o l i t i c a l l e a d e r s a n d t h a t ma ke s u se o f ad va n c e s i n p l a n n i n g p r o c e d u r e s a n d t e c h n i q u e s. F o r t h i s r e a s o n, s o me p l a n n e r s b e l i e ve t h a t d i e p u b l i c a t i o n o f a s i n gl e l o n g - r a n ge ma s t e r t r a n s p o r t a t i o n p l a n s h o u l d be a vo i d e d ( I). R a t h e r, t r a n s p o r t a t i o n p l a n n i n g a ge n c i e s s h o u l d c o n s i d e r t h e practice of updating and publishing transportation plans or reports on a p e r i o d i c b a s i s, fo r e xa m p l e , e ve r y t wo ye a r s . Tra n s p o r t a t i o n p l a n n i n g c o n s i s t s o f t h r e e l e ve l s o f p l a n n i n g: ( 1 ) p o l i c y p l a n n i n g, ( 2 ) s ys t e m s p l a n n i n g, a n d ( 3 ) p r o j e c t o r fa c i l i t y p l a n n i n g. P ol i c y p l a n n i n g i s c o n c e r n e d wi t h t h e e s t a b l i s h me n t o f t r a n s p o r t a t i o n p o l i c y a n d t h e d e ve l o p m e n t o f go a l s a n d o b j e c t i ve s . It i s “i n vo l v e d wi t h q u e s t i o n s o f r e s o u r c e a l l o c a t i o n . . . , b o t h i n t e r ms o f a l l o c a t i o n b y ge o gr a p h i c a r e a a n d b y t r a n s p o r t a t i o n mo d e . It i s n o t i n vo l ve d wi t h t h e r e vi e w o r r e c o m m e n d a t i o n o f s p e c i fi c fa c i l i t i e s o r c o r r i d o r s o r e ve n t r a n s p o r t a t i o n n e t wo r ks ” ( 2 ). S ys t e m s p l a n n i n g i s “a p r o c e s s u n d e r wh i c h t r a n s p o r t a t i o n n e t wo r ks a n d c o r r i d o r s a r e d e fi n e d . . . , s t a r t i n g fr o m fo r e c a s t s o f p o p u l a t i o n a n d e c o n o m i c gr o wt h a n d c o n t i n u i n g t h r o u gh e s t i ma t e s o f p e r s o n a n d go o d s

t o a pOhNysPiLcA a lN dNeI sNcGr i p t i o n o f t h e s ys t e ms r e q u i r e d t o me e t t. i i o s e 134 m To R ve A NmSePnOt RTATI r e a l o r i m p l i e d n e e d s ” ( 2 ). P ro j e c t o r fa c i l i t y p l a n n i n g i s c o n c e r n e d p r i ma r i l y wi t h d e t e r mi n i n g t h e s c a l e a n d l a yo u t o f i n d i vi d u a l fa c i l i t i e s t o a cc o m mo d a t e t h e a n t i c i p a t e d d e m a n d . In a s l a t e h i gh wa y a ge n c y t h i s l e ve l o f p l a n n i n g i s n o r ma l l y p e r fo r m e d b y m o d a l d i vi s i o n s ( a vi a t i o n , h i gh wa ys , e t c . ) o r, i n a fu n c t i o n a l o rga n i z a t i o n , b y t h e d e s i gn d i vi s i o n . As p e c t s o f p r o j e c t p l a n n i n g a r e c o ve r e d i n o t h e r c h a p t e r s o f t h i s t e xt a n d wi l l n o t b e d i s c u s s e d fu r t h e r here. P l a n n i n g m a y b e s u b d i vi d e d i n t o t h r e e c a t e go r i e s t o a cc o u n t fo r d i ffe r e n c e s i n t he p l a n n i n g p e r i o d : 1 , L o n g- r a n ge p l a n n i n g.

2 , In l e r m e d i a l e - ra n ge p l a n n i n g. 3 , S h o r t - r a n ge p l a n n i n g.

Transportation Planning 135

L o n g r a n ge p l a n n i n g i s t yp i c a l l y co n d u c t e d fo r a p e r i o d o f a b o u t 1 5 t o 3 0 ye a r s i n t o t h e fu t u r e ( 5 ) . 'T h e l e ve l o f d e t a i l fo r s u c h p la n n i n g i s ge n e r a l i z e d , a n d l o n g - r a n ge p l a n s s h o u l d h e p e r i o d i c a l l y r e a p p r a i se d a n d c h a n ge d t o a c c o u n t . fo r u n e xp e c t e d s h i ft s i n p o p u la t i o n , d e ve l o p me n t , a n d s o fo r t h . In t e r m e d i a t e - r a n ge p l a n n i n g c o ve r s a p e r i o d o f'a b o u t 5 t o 1 5 ye a r s i n t h e fu t u r e . “ In t h i s p l a n n i n g p ha s e , t h e fa c i l i t y c h a r ac t e r i s t i c s a n d p e r fo r m a n c e , a s we l l a s r o u t e l o c a t i o n, wo u l d Ir e mo r e s p e c i fi c , wi t h e va l u a t i o n o f a l t e r n a t i ve d e s i gn s a n d r o u t e l oc a t i o n s i n t e r ms o f a p e r fo r m a n c e a n a l ys i s , i nc l u d i n g t r a d i t i o n a l b e n e fi t / c o s t a n a l ys i s , as we l l a s e n vi r o n m e n t a l i m p a c t s a n d d e ve l o p me n t a l c o n s i d e ra t i o n s ” ( J ). S h o r t - r a n ge p l a n n i n g i s t yp i c a l l y c o n d u c t e d fo r a p e r i o d o f a b o u t fi ve ye a r s . In s h o r t r a n ge p l a n s, t he p h ys i c a l fe a t u r e s o f t r a n s p o r t fa c i l i t i e s a n d t i r e t ra ffi c a n d l a n d d e ve l o p m e n t s t h a t t h e s e fa c i l i t i e s a r e e xp e c t e d t o s e r ve c a n b e s p e c i fi e d i n c o n s i d e r a b l e d e t a i l a n d wi t h re a s o n a b l e p r e c i s i o n.

6-2 Organization A s i n d i c a t e d i n C h a p t e r 2, s t a t e t r a n s p o r t a t i o n d e p a r t me n t o rga n i z a t i o n a l s t r u c t u r e s m a y h e c l a s s i fi e d a s mo d a l , fu n c t i o n a l , o r mi xe d mo d a l a n d fu n c t i o n a l . { S e e F i gu r e 2 - 2 ). B e c a u s e o f d i ffe r i n g n e e d s a n d c a p a b i l i t i e s a m o n g t h e va r i o u s s t a t e s , , t h e r e i s n o s i n gl e i d e a l o rga n i z a t i o n a l s t r uc t u r e t h a t wo u l d h e s u i t a b l e fo r al l s l a t e s. S o m e p l a n n e r s r e c o m me n d t h a t p o l ic y p l a n n i n g a n d s ys t e ms p l a n n i n g b e p e r fo r m e d b y a s i n gl e p l a n n i n g u n i t t h a t r e p o r t s d i r e c t l y t o t h e c h i e f e xe c u t i ve o f t h e t r a n s p o r t a t i o n d e p a r t me n t { . ? ). In a d e pa r t me n t wi t h a fu n c t i o n a l o r m i xe d o rga n i z a t i o n a l s t r u c t u r e , t h e p l a n n i n g u n i t mi gh t b e o n e o f t h e p r i n c i p a l o p e r a t i n g ( o r l i n e ) d i vi s i o n s . In a mo d a l o rga n i z a t i o n , t h e p l a n n i n g u n i t i s m o r e l i ke l y t o b e a s t a ff- l e ve l o rga n i z a t i o n wi t h t h e p l a n n i n g d i r e c t o r r e p o r t i n g d i r e c t l y t o t h e c h i e f e xe c u t i ve o ffi c e r. An o t h e r r e c o m m e n d a t i o n (4) c a l l s fo r a s t a ff- le ve l u n i t fo r p o l i c y p l a n n i n g a n d a l i n e - l e ve l u n i t fo r s ys t e m s p l a n n i n g. B e c a u s e o f t h e n a t u r e o f t h e p l a n n i n g fu n c t i o n , a mu l t i d i s c i p l i n a r y s t a ff i s p r e fe r r e d . Typ i c a l l y, a s t a t e wi d e t r a n s p o r t a t i o n p l a n n i n g u n i t wi l l h e c o m p r i s e d o f p e r s o n s fr o m a va r i e t y o f d i s c i p l i n e s i n c l u d i n g transportation p l a n n e r s / e n gi n e e r s , e n vi r o n me n t a l i s t s , t ra n s p o r t a t i o n e c o n o m i s t s , p u b l i c fi n a n c e s pe c i a l i s t s , b e h a vi o r a l p s yc h o l o gi s t s , an d s o c i o l o gi s t s . It i s a l s o i m p o r t a n t t h a t p o l i c ie s a n d p l a n s Ir e d e ve l o p e d wi t h b r o a d i n vo l ve m e n t o f 'o i l i e r a ge n c i e s , i n t e r e s t gr o u p s , a n d i n d i vi d u a l c i t i z e n s. G e n e r a l l y, t h e fo l l o wi n g t yp e s o f a ge n c i e s , gr o u p s , a n d i n d i vi d u a l s s h o u l d contribute to the planning process (2): 1 . Th e s t a t e l e gi s l a t u r e . 2 . G e n e r a l p o l i c y a n d b u d ge t a r y gr o u p s i n t h e e xe c u t i ve b r a n c h o f t h e s t a t e go ve r n m e n t . 3 . O t h e r s l a t e a ge n c i e s s u c h a s t he i n d u s t r i a l d e ve l o p me n t d e p a r t me n t , p u b l i c s e r vi c e c o m m i s s i o n , r e c r e a t i o n c o m mi s s i o n , a n d t r a ve l

136 T R A N S P O RTATI O N P L A N N I N G 4. 5. 6. 7. 8.

commission. R e gi o n a l a n d l oc a l p l a n n i n g c o m mi s s i o n s . S p e c i a l i n t e r e s t gr o u p s , P r i va t e t r a n s p o r t a t i o n co mp a n i e s , M u h i s t a t e c o o r d i n a t i n g gr o u p s , C i t i z e n s a n d c i t i z e n s gr o u p s .

P l a n n e r s o f fe d e r a l l y a s s i s t e d p r o j e c t s i n t h e U n i t e d S t a t e s mu s t n o w c o o r d i n a t e t h e p l a n n i n g a c t i vi t y t h r o u gh a n a r ea wi d e o r s t a t e c l e a r i n gh o u s e ( 5 ) . In m e t r o p o l i t a n a r e a s, t h e c l e a r i n gh o u s e i s a n a r e a wi d e a ge n c y { e . g. , a r e gi o n a l p l a n n i n g c o m m i s s i o n ) t h a t h a s b e e n r e c o gn i z e d b y t he O ffi c e o f M a n a ge m e n t a n d B u d ge t a s a n a p p r o p r i a te a ge n c y t o e va l u a t e , r e vi e w, a n d c o o r d i n a t e fe d e r a l l y a s s i s t e d p r o gr a ms a n d p r o j e c t s . In n o n me t r o p o l i t a n a r e a s , t he c l e a r i n gh o u s e i s a c o mp r e h e n s i ve p l a n n i n g a ge n c y de s i gn a t e d b y t h e go ve r n o r o r b y s t a t e l a w t o r e vi e w a n d c o o r d i n a t e s u c h a c t i vi t i e s . Typ i c a l l y, c o o r d i n a t i o n wi t h p u b l i c a ge n c i e s , p r i va t e gr o u p s , a n d i n d i vi d u a l s i s a c c o m p l i s h e d b y t h e e s t a b l i s h me n t o f t wo o r mo r e c o m m i t t e e s . L o r e xa m p l e , a t e c h n i c a l r e vi e w c o m mi t t e e mi gh t b e fo r me d c o n s i s t i n g o f i n d i vi d u a l s r e p r e s e n t i n g go ve r n m e n t a l a ge n c i e s , c o m mi s s i o n s , a n d s o fo r t h . A c i t i z e n s a d vi s o r y co m mi t t e e c o u l d b e fo r me d wi t h r e p r e s e n t a t i ve s o f c i vi c o rga n i z a t i o n s , s p e c i a l i n te r e s t gr o u p s , a n d c i t i z e n s . It wi l l b e r e c a l l e d fr o m C ha p t e r 4 t h a t c u r r e n t r e gu l a t i o n s r e q u i r e t h a t, c i t i z e n s he gi ve n t h e o p p o r t u n i t y t o p a r t i c i p a t e i n p u b l ic h e a r i n gs r e ga r d i n g t h e c o n s t r u c t i o n o f c e r t a i n fe d e r a l l y a s s i s t e d h i gh wa y p r o j e c t s . S u c h h e a r i n gs gi ve t h e c i t i z e n s t h e o p p o r t u n i t y t o c o mme n t o n s u c h p r o j e c t s at t h e c o r r i d o r o r d e s i gn s t a ge .

POLICY PLANNING 6-3 The Policy Planning Process P ol i c y p l a n n i n g i s a d e l i b e r a t e p r o c e s s t h a t l e a d s t o a s e t o f c o o r d i n a t e d p o l i c y d e c i s i o n s d e s i gn e d t o a c h i e ve a de fi n e d s e t o f go a l s a n d o b j e c t i ve s ( 2 ) . It e s t a b l i s h e s b r o a d d i r e c t i o n fo r a s t a t e o r l o ca l go ve r n me n t i n t r a n s p o r t a t i o n m a t t e r s . It i s a me a n s o f d e s c r i b i n g i n a ge n e r a l wa y wh a t i s t o b e d o n e , wh o i s t o d o i t, h o w i t i s t o b e d o n e, a n d wi t h i n wh a t constraints. P ol i c y p l a n n i n g i n c l u d e s t h e fo l l o wi n g t yp e s o f a c t i vi t i e s ( 6 ) ; 1 . Id e n t i f yi n g p r o b l e m s , o p t i o n s , a n d a l t e r n a t i ve c o u r s e s o f transportation actions. 2 . In t e r p r e t i n g i n fo r m a t i o n a n d a n a l yt i c a l d a t a fo r p o l i c ym a k e r s a n d citizens. 3 . M o n i t o r i n g a n d a n a 1 v z i n g fe d e r a ! l e gi s t a t i o n a n d e v a 1 u a t i n g i t s i mp a c t o n s t a t e o r l o c a l p o l i c y. 4 . P r o vi d i n g r e s o u r c e ma t e r i a l s fo r ma n a ge m e n t a n d p u b l i c i n fo r ma t i o n personnel.

6-4 Goals and standards of transportation planning A n i m p o r t a n t fu n c t i o n o f p o l i c y p l a n n i n g i s t h e e s t a b l i s h me n t an d a r t i c u l a t i o n o f go a l s o r o b j e c t i ve s . To p l a n n e r s , go a l s ar e e xp r e s s i o n s o f

Systems Planning 137 p u r p o s e s t o wa r d wh i c h p l a n s a r e d i r e c t e d . Tra n s p o r t a t i o n p l a n s a r e b a s e d o n s u c h go a l s a s r e d u c i n g t r a ffi c c o n ge s t i o n , p r o vi d i n g sa fe t r a ve l , c o n s e r vi n g e ne rgy, fo s t e r i n g ec o n o mi c gr o wt h , a n d p r e s e r vi n g a n d e n h a n c i n g t he e n vi r o n m e n t . To t h e e xt e n t p o s s i b l e, go a l s o r o b j e c t i ve s s h o u l d b e s t a t e d i n s p e c i fi c a n d me a s u r a b l e te r ms an d s h o u l d h e a c c o m p a n i e d b y s t a n d a r d s o r c r i t e r i a b y wh i c h go a l pe r fo r ma n c e i s t o Ir e m e a s u r e d . F o r e xa m p l e , o ne o f t he o b j e c t i ve s l i s t e d b y t h e s t a t e o f Wis c o n s i n wa s “ t o p r o vi d e a p l a n wh i c h i s b o t h ec o n o mi c a l a n d e ffi c i e n t , s a t i s f yi n g a l l o t h e r o b j e c t i ve s a t t h e l o we s t p o s s i b l e c o s t " (. 5 ) . Th e s t a n d a r d s u s e d t o m e a s u r e t h a t o b j e c t i ve we r e a s fo l l o ws : 1 . 'T h e s u m o f t h e h i gh wa y t ra n s p o r t a t i o n s ys t e m’s c a p i t a l c o s t s a n d u s e r s ’ o p e r a t i n g c o s t s s h o u l d b e mi n i mi z e d . 2 . Th e fu l l e s t e c o n o m i c u s e s h o u l d h e ma d e o f e xi s t i n g a n d c o m mi t t e d m a j o r h i gh wa y fa c i l i t i e s , 3 . Ad d i t i o n a l h i gh wa y fa c i l i t i e s s h o u l d he p r o vi d e d t o s e r ve o r i n d u c e fu t u r e t r a ve l d e m a n d at t h e d e s i r e d l e ve l o f s e r vi c e .

SYSTEMS PLANNING G r e a t d i ffe r e n c e s e xi s t a m o n g t h e va r i o u s h i gh wa y a ge n c i e s a t t h e s ys t e ms l e ve l o f p l a n n i n g i n t e r ms o f b o t h n e e d s a n d l e ve l o f s o p h i s t i c a t i o n e m p l o ye d . At t h i s l e ve l o f'p l a n n i n g, t r a n s p o r t a t i o n l i n ks a n d n e t wo r k s a r e d e fi n e d , fo r e c a s t s o f fu t u r e t r a ffi c a r e ma d e , a n d t h e p h ys i c a l fa c i l i t i e s r e q u i r e d t o s e r ve fu t u r e n e e d s a r e d e sc r i b e d , Tra d i t i o n a l p l a n n i n g p r o c e d u r e s, wh i c h a r e s t i l l e mp l o ye d i n a n u m b e r o f s t a t e s , e s t a b l i s h ne e d s fo r i mp r o ve m e n t s o n a l i n k- t o - l i n k b a s i s r a t h e r t h a n s ys t e m wi d e . In t h o se s t a t e s, h i gh wa y n e e d s a re e s t a b l i s h e d t o s o m e e xt e n t s u b j e c t i ve l y o n t h e b a s i s o f va r i o u s s u r ve ys i n c l u d i n g h i gh wa y i n ve n t o r i e s , t r a ffi c s u r ve ys , r o a d - l i fe s t u d i e s , a n d h i gh wa y s u ffi c i e n c y s t u d i e s . D a t a fr o m s u c h s u r ve ys p r o vi d e a b a s i s fo r p r o j e c t i o n s o f t r e n d s a n d t h e i d e n t i fi c a t i o n a n d r a n ki n g o f h i gh wa y i mp r o ve m e n t n e e d s. In c r e a s i n g l y, s t a t e a ge n c i e s a r e p e r fo r mi n g s t a t e wi d e t r a n s p o r t a t i o n p l a n n i n g b y e m p l o yi n g p l a n n i n g p r o c e d u r e s t ha t h a ve b e e n wi d e l y u s e d t o d e ve l o p u r b a n t r a n s j 3 0 r i . a t . i o n p l a n s . Typ i c a l l y, s u c h p r o c e d u r e s c o n s i d e r t r a n s p o r t n e e d s o n a n e t wo r k o r s ys t e m wi d e b a s i s a n d i n c l u d e t he fo l l o wi n g s e q u e n t i a l a c t i vi t i e s o r s t e p s : 1 . D a t a c o l l e c t i o n. 2 , D a t a a n a l ys i s , 3 , P l a n ge n e r a t i o n a n d e va l u a t i o n . 4 . Im j i l e m e n t a t i o n o f t h e p l a n .

6-5 Collection of data to measure existing transportation conditions To p l a n i n t e l l i ge n t l y, p l a n n e r s mu s t h a ve a gr e a t d e a l o f d a t a o n t h e t r a n s p o r t a t i o n s ys t e m a n d i t s u s e . Th e y o b t a i n s u c h d a t a b y ma ki n g s t u d i e s o n t h e e xt e n t , u s e , a n d c o n d i t i o n o f e xi s t i n g fa c i l i t i e s ; t h e l i fe e xp e c t a n c y o f t h e s ys t e m ; a n d t h e n a t u r e a n d e xt e n t o f t r a i l i e s e r ve d . S o me o f t h e s e s t u d i e s a r e d e s c r i b e d i n t h e fo l l o wi n g p a r a gr a p h s .

138 T R A N S P O RTATI O N P L A N N I N G Road inventory F o r m a n y ye a r s , va r i o u s h i gh wa y a ge n c i e s h a ve c o n d u c t e d r o a d i n ve n t o r i e s , recording i n fo r ma t i o n on the mi l e a ge s , p h ys i c a l c h a r a c t e r i s t i c s, a n d c o n d i t i o n o f a l l r o a d s i n t h e s ys t e m. Th e fo l l o wi n g t yp e s o f i n fo r m a t i o n s h o u l d b e c o l l e c t e d i n a r o a d i n ve n t o r y: 1. 'T h e fu n c t i o n a l r o a d wa y c l a s s . 2. 'T h e c l a s s i fi c a t i o n b y t yp e o f p a ve me n t . 3. Th e t yp e , d i m e n s i o n s , a n d c o n d i t i o n o f a l l s t r u c t u r e s . 4. Th e l o c a t i o n s o f fa r ms , r u r a l d we l l i n gs , s c h o o l s, c h u r c he s , a n d other c u l t u r a l fe a t u r e s . 5. Th e p h ys i c a l d e s i gn fe a t u r e s i n c l u d i n g pa ve me n t wi d t h s , gr a d e s , c u r va t u r e , s i gh t d i s t a n c e s, l o c a t i o n o f r o a d wi d e o b s t a c l e s, a n d o i l i e r h a z a r d s. M a n y h i gh wa y a ge n c i e s d i s p l a y r o a d i n ve n t o r y i n fo r ma t i o n o n ma p s s i m i l a r t o t h a t , s h o wn a s F i gu r e 6 - 1. Th e y ma ke o t h e r ma p s b y r e p r o d u c i n g t h e b a s e m a p s a n d a d d i n g o t h e r d e s i r e d i n fo r ma t i o n . F o r e xa mp l e , t h e a ge n c y m a y m a ke m a p s s h o wi n g ( 1 ) s u r fa c e c o n d i t i o n s a n d t yp e o f s u r fa c e , ( 2 ) c o m m o n c a r r i e r, b u s, a n d t r u c k r o u t e s , ( 3 ) p o s t a l a n d sc h o o l b u s r o u t e s , a n d ( 4 ) a ve r a ge d a i l y t r a ffi c . H i gh wa y a ge n c i e s s h o u l d ma i n t a i n a n u p - t o - d a t e i n ve n t o r y o f r o a d s u n d e r t h e i r j u r i s d i c t i o n . If t h i s l i a s n o t b ee n d o n e , a r o a d i n ve n t o r y s h o u l d be made and maintained. Road-use studies H i gh wa y p l a n n e r s p e r fo r m r o a d - u s e s t u d i e s t o d e t e r mi n e t h e r e l a t i ve u s e o f va r i o u s p a r t s o f a h i gh wa y s ys t e m. In fo r ma t i o n ma y b e o b t a i n e d b y p e r s o n a l i n t e r vi e ws wi t h a r e p r e s e n t a t i ve s a mp l e o f t h e r e gi s t e r e d mo t o r ve h i c l e o pe r a t o r s wi t h i n t h e h i gh wa y j u r i s d i c t i o n . D r i ve r s a re a s ke d t o s t a t e t h e t o t a l m i l e a ge d r i ve n i n o n e ye a r an d t h e p r o p o r t i o n o f t h a t mi l e a ge t h a t wa s d r i ve n o n va r i o u s c l a s s i fi c a t i o n s o f s t r e e t s a n d h i gh wa ys , Th e p l a n n e r s c a n u s e s u c h i n fo r ma t i o n t o d e t e r mi n e t h e p r o p o r t i o n a te u s e ma d e o f t h e va r i o u s r o a d s b y u r b a n , s u b u r b a n, a n d r u r a l r e s i d e n t s. B y c o r r e l a t i o n wi t h fi n a n c i a l d a t a , p l a n n e r s ma y t h e n c o mp a r e t he b e n e fi t s r e c e i ve d wi t h t h e r e ve n u e s c o n t r i b u t e d b y va r i o u s gr o u p s o f c i t i z e n s . M a n y s t a te s u s e s u c h i n fo r m a t i o n t o m o r e e q u i t a b l y d i s t r i b u t e t h e co s t s o f h i gh wa y t r a n s p o r t a t i o n a m o n g t h e va r i o u s b e n e fi t i n g gr o u p s i n a c c o r d a n c e wi t h t h e c o n c e p t s p re s e n t e d i n C h a p t e r 2. Road-life studies S t a t e h i gh wa y a ge n c i e s h a ve b e e n co n d u c t i n g r o a d - l i fe s t u d i e s s i n c e t h e m i d - 1 9 3 0 s. Th e p r i m a r y o b j e c t i ve s o f s u c h s t u d i e s a r e t o d e te r mi n e t h e a ve r a ge r a t e o f r e t i r e m e n t a n d t h e es t i ma t e d a ve r a ge s e r vi c e l i fe fo r e a c h t yp e o f h i gh wa y s u r fa c e . R o a d s a r e u s u a l l y r e t i r e d b y r e s u r fa c i n g, r e c o n s t r u c t i n g, o r

Systems Planning 139

GENERAL HIGHWAY MAP

SUMTER COUNTY GEORGIA

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FIGURE 6-1 A genera] highway map. (Courtesy Georgia Department of'Transportation.)

140 T R A N S P O RTATI O N P L A N N I N G

Systems Planning 141 a b a n d o n i n g t h e m . In fo r m a t i o n i s a l s o a s s e mb l e d o n c o s t s o f c o n s t r u c t i o n, maintenance, and depreciation. Wit h t h i s i n fo r m a t i o n , p l a n n e r s ma y e s t i ma t e t h e a mo u n t a n d c o s t o f r e p l a c e m e n t s t h a t wi l l b e r e q u i r e d i n t h e fu t u r e . Th e y c a n p r o gr a m c o n s t r u c t i o n a n d r e c o n s t r u c t i o n o p e r a t i o n s o n t h e b a s i s o f a n t i c i pa t e d fu t u r e r e ve n u e r e c e i p t s. H i gh wa y e n gi n e e r s u s e r o a d - l i fe d a t a i n e c o n o mi c c a l c u l a t i o n s, a s t h e p r e vi o u s c h a p t e r i n d i c a t e d . Traffic volume studies E n gi n e e r s a n d p l a n n e r s h a ve b e e n co n d u c t i n g t r a ffi c vo l u me s t u d i e s fo r m o r e t h a n 4 0 ye a r s . 'T h e p r o c e d u r e s u s e d i n s uc h s t u d i e s a r e we l l d o c u m e n t e d e l s e wh e r e (7,8) a n d wi l l b e o n l y b r i e fl y d e s c r i b e d i n t h i s s e c t i o n . Tra ffi c vo l u m e s t u d i e s p r o vi d e h i gh wa y o ffi c i a l s wi t h e s s e n t i a l i n fo r m a t i o n o n t h e a m o u n t o f u s a ge o f t h e r o a d s i n t h e h i gh wa y s ys t e m. S u c h i n fo r m a t i o n i s n e e d e d fo r “t h e d e t e r mi n a t i o n o f d e s i gn s t a n d a r d s , t i n e s ys t e m a t i c c l a s s i fi c a t i o n o f h i gh wa ys a n d t h e d e ve l o p me n t o f p r o gr a ms fo r i m p r o ve m e n t a n d m a i n t e n a n c e ” ( 9 ) . F r o m t r a ffi c vo l u me s t u d i e s , p l a n n e r s m a y e s t i m a t e t h e ve h i c l e - mi l e s o f t r a ve l o n t h e va r i o u s c la s s e s o f r u r a l a n d u r b a n r o a d wa ys . S u c h t r a ve l d a t a i n d i c a t e a me a s u r e o f s e r vi c e p r o vi d e d b y t h e s ys t e m a n d fa c i l i t a t e t h e a p p r a i s a l o f s a fe t y p r o gr a ms a n d t h e d e ve l o p m e n t o f e q u i t a b l e h i gh wa y fi n a n c e a n d t a xa t i o n p r o gr a ms . T h e fu n d a m e n t a l m e a s u r e fo r t r a ffi c vo l u me s t u d i e s i s a n n u a l a ve r a ge d a i l y t r a ffi c (ADT). B y u s i n g e mp i r i c a l l y- b a s e d r e l a t i o n s h i p s, ADT va l u e s c a n e a s i l y b e c o n ve r t e d t o p e a k h o u r l y vo l u me s , B e c a u s e o f t h e wi d e va r i a b i l i t y o { Tra ffi c fl o ws d u r i n g d i ffe r e n t t i me s a n d a t d i ffe r e n t l o c a t i o n s, i t i s p r a c t i ca l l y i mp o s s i b l e t o a r r i ve a t a t r u e a c c o u n t i n g o f t h e t ra ffi c vo l u me s o n e a c h s ec t i o n wi t h i n a h i gh wa y s ys t e m. E ve n i f c o m p r e h e n s i ve a n d c o n t i n u o u s mo n i t o r i n g o f t r a ffi c we r e p o s s i b l e , t h e c o s t s o f m a i n t a i n i n g s u c h a co u n t i n g p r o gr a m wo u l d b e p r o h i b i t i ve . Tra ffi c vo l u m e s t u d i e s a r e t h e r e fo r e c a r r i e d o u t o n a s a mp l e ba s i s . M a n y h i gh wa y a ge n c i e s h a ve e s t a b l i s h e d s ta t e wi d e o r a r e a wi d e t r a ffi c c o u n t i n g p r o gr a m s . In s u c h p r o gr a ms , t r a ffi c vo l u me s a r e me a s u r e d b y m e a n s o f a l a rge n u m b e r o f s h o r t c o u n t s c o ve r i n g a n e n t i r e s t a t e o r a r e a. T h e l o c a t i o n s fo r t he c o u n t s a r e c a l le d coverage stations. C o ve r a ge s t a t i o n s a r e t yp i c a l l y s p a c e d a t i n t e r va l s o f 2 t o 5 mi l e s a l o n g r u r a l h i gh wa ys an d a b o u t 3 m i l e a p a r t a l o n g u r b a n h i gh wa ys a n d s t r e e t s. M e a s u r e me n t s a t c o ve r a ge s t a t i o n s a r e t yp i c a l l y r e c o r de d o n p o r t a b l e c o u n t e r s a c t u a t e d b y p n e u m a t i c d e t e c t o r s. At c o ve r a ge s t a t i o n s, t h e t r a ffi c vo l u me i s n o t m o n i t o r e d c o n t i n u o u s l y b u t i s s a mp l e d o ve r t i me . Th e d u r a t i o n a n d fr e q u e n c y o f s u c h c o u n t s ge n e r a l l y d e p e n d o n t h e c l a s s o f t h e s t r e e t o r h i gh wa y a n d t h e a m o u n t o f t r a ffi c i t s e r ve s . Typ i c a l l y, c o ve r a ge c o u n t s c o n s i s t o f a s i n gl e n o n d i r e c t i o n a i 2 4 - o r 4 8 - h r c o u n t r e p e a te d a t fo u r - ye a r i n t e r va l s . In o r d e r t o c o n ve r t c o ve r a ge c o u n t s t o e s t i ma t e s o f a ve r a ge d a i l y t r a ffi c , t r a ffi c vo l u m e s a r e me a s u r e d a t a s ma l l n u mb e r o f s t r a t e gi c a l l y s e l e c l e d control stations. At t h o s e l o c a t i o n s , t r a ffi c c o u n t s a r e u s u a l l y ma d e

142 T R A N S P O RTATI O N P L A N N I N G

o ve r a 7 - d a y p e r i o d t o me a s u r e h o u r l y a n d d a i l y t r a ffi c p a t t e r n s o f va r i a t i o n . In a d d i t i o n, 2 4 - h r n o n d i r e c t i o n a l c o u n t s a r e n o r ma l l y ma d e at c o n t r o l s t a t i o n s o n a m o n t h l y b a s i s t o me a s u r e t h e s e a s o n a l va r i a t i o n . O n t h e b a s i s o f t e m p o r a l p a t t e r n s o f va r i a t i o n me a s u r e d a t t he c o n t r o l s t a t i o n s , t h e s a m p l e c o ve r a ge c o u n t s c a n b e a d j u s t e d b y c o r r e c t i o n fa c t o r s t o p r o vi d e e s t i m a t e s o f ADT t h r o u gh o u t t h e s ys t e m. In a n u m b e r o f h i gh wa y j u r i s d i c t i o n s, p e r ma n e n t c o u n t i n g s ta t i o n s h a ve b e e n e s t a b l i s h e d a t a s ma l l n u mb e r o f s e le c t e d l o c a t i o n s. At . t h o s e l o c a t i o n s , t r a ffi c vo l u m e s a r e me a s u r e d c o n t i n u o u s l y, p r o vi d i n g a n a c c u r a t e m e a s u r e o f t h e h o u r l y, d a i l y, a n d se a s o n a l p a t t e r n s o f va r i a t i o n . G e n e r a l l y, a u t o m a t i c t r a ffi c d e t e c t i o n a n d r ec o r d i n g e q u i p me n t i s e mp l o ye d a t c o n t i n u o u s c o u n t i n g s t a t i o n s, a n d i n s o me s t a t e s t r a ffi c , vo l u me d a t a a r e t r a n s m i t t e d t o a c e n t r a l c o mp u t e r o ve r t e l e p h o ne l i n e s fo r p r o c e s s i n g a n d a n a l ys i s (10, 11). Tra ffi c c o u n t s m a d e wi t h a u t o ma t i c de vi c e s ge n e r a l l y mu s t b e s u p p l e m e n t e d b y m a n u a l s u r ve ys t o r e c o r d i n fo r ma t i o n o n t h e c h a r a c t e r o f t r a ffi c . S u c h s u r ve ys a r e o ft e n u n d e r t a ke n a t we i gh i n g o r l o a d o me t e r s ta t i o n s , T h e r e , i n fo r m a t i o n i s c o l l e c t e d o n t h e t yp e o f ve h i c l e , i t s le n gt h , wi d t h , a n d h e i gh t , t h e ra t e d c a p a c i t y, a n d t h e a xl e a n d gr o s s l o a d s . Ad d i t i o n a l i n fo r m a t i o n o n t h e t yp e o f c o mmo d i t y ca r r i e d , t h e o r i gi n , t h e d e s t i n a t i o n, a n d o t h e r p e r t i n e n t fa c t s ma y a l s o b e n o t e d. Wh e n a l l t h e i n fo r ma t i o n o f t h e t r a ffi c s u r ve y Ir a s b e e n a s s e mb l e d , t h e e xp a n s i o n fa c t o r s h a ve b e e n d e t e r m i n e d , a n d t he a n n u a l a ve r a ge 2 4 - h r t r a ffi c h a s b e e n c o mp u t e d , t r a ffi c m a p s a n d fl o w m a p s c a n b e p r e p a r e d. A b a s e ma p p r e vi o u s l y p r e pa r e d b y t h e r o a d i n ve n t o r y s u r ve y i s u s e d fo r t h e t r a ffi c ma p . 'l i r e n u me r i c a l t r a ffi c vo l u m e s fo r e a c h s e gm e n t o f t h e r o a d a r e u s u a l l y p l a c e d o n t h i s ma p . F o r m o r e r a p i d vi s u a l i z a t i o n , t h e vo l u me o f t r a ffi c ma y b e s h o wn o n t h e t r a ffi c fl o w m a p b y b a n d s p r o p o r t i o n a l i n wi d t h t o t h e vo l u me o f t r a ffi c p a s s i n g t h r o u gh t h e va r i o u s p o i n t s a t wh i c h b a s e s t a t i o n c o u n t s we r e t a ke n . F i gu r e 6 - 2 s h o ws a t yp i c a l t r a ffi c fl o w ma p . Travel surveys Tra ve l s u r ve ys i d e n t i f y wh e r e a n d wh e n t r i p s b e gi n an d e n d, t h e t r i p p u r p o s e , t h e m o d e o f t r a ve l , a s we l l a s c e r t a i n s oc i a l a n d e c o n o mi c c h a r a c t e r i s t i c s o f t h e t r i p ma ke r. S u c h s u r ve ys ma y a l s o d e te r mi n e t h e t yp e s o f l a n d u s e a t t r i p t e r mi n i , a u t o mo b i l e oc c u p a n c y, a n d , fo r fr e i gh t , t h e t yp e o f c o m m o d i t y t r a n s p o r t e d . Tra ve l s u r ve ys s e r ve as a fu n d a me n t a l s o u r c e o f d a t a fo r u r b a n t r a n s p o r t a t i o n s t u d i e s a n d a r e be i n g i n c r e a s i n gl y u s e d i n s t a t e wi d e t r a n s p o r t a t i o n s t u d i e s (10, 11). B y m e a n s o f t r a ve l s u r ve ys , p l a n n e r s at t e mp t t o o b t a i n a s a mp l e c r o s s s e c t i o n o f a l l t r a ve l o n a t yp i c a l d a y wi t h i n a s p e c i fi e d a r e a. B y e xp a n d i n g t h e d a t a , t he y a r e a b l e t o p r o d u c e an e s t i ma t e o f t h e a ve r a ge t r a ve l d e ma n d o n t h e t r a n s p o r t a t i o n s ys t e m a t t he l i me t h e s u r ve y wa s c o n d u c t e d. T h e r e a r e fo u r ge n e r a l c l a s s i fi c a t i o n s o f t ra ve l s u r ve ys : 1. 2.

H o u s e h o l d t r a ve l s u r ve ys . R o a d s i d e s u r ve ys .

Systems Planning 143 3. 4.

M o d a l s u r ve ys , G o o d s m o ve m e n t s u r ve ys .

144 T R A N S P O RTATI O N P L A N N I N G

SCALE OF THE TR AFFIC BANOS

FIGURE 6-2 A portion of a traffic (low map. (Courtesy Georgia Department of Transportation.)

Systems Planning 145 Household travel surveys 'T h e s e s u r ve ys a r e e s p e c i a l l y u s e fu l fo r de t e r mi n i n g t h e n u m b e r a n d c ha r a c t e r i s t i c s o f p e r s o n - t r i p s o r a u t o - d r i ve r t r i p s ma d e b y r e s i d e n t s wi t h i n a s pe c i fi e d s t u d y a r e a . B y s u c h s u r ve ys , p l a n n e r s ma y c o l l e c t e xt e n s i ve d a t a o n s o c i oe c o n o mi c c h a r a c te r i s t i c s o f h o u s e h o l d s a n d r e l a t e s u c h i n fo r m a t i o n t o h o u s e h o l d t r a ve l . S u c h r e l a t i o n s h i p s a r e e xt r e m e l y va l u a b l e fo r m a ki n g fo r e c a s t s o f fu t u r e t r a ve l b y p e r s o n s wh o r e s i d e i n t h e s t u d y a r e a (11). H o u s e h o l d t r a ve l s u r ve ys i n c l u d e h o me i n t e r vi e w, t e l e p h o n e , a n d ma i l s u r ve ys . T h e h o m e i n t e r vi e w me t h o d i n vo l ve s i d e n t i f yi n g a s a mp l e o f a l l o f t h e h o u s e h o l d s wi t h i n d i e s u r ve y ar e a , a r r a n gi n g fo r i n t e r vi e ws , a n d q u e s t i o n i n g r e s p o n d e n t s a b o u t t r i p s ma d e b y p e r s o n s i n t h e i r r e s p e c t i ve h o u s e h o l d s t h e p r e vi o u s d a y. Th e s a mp l e s i z e va r i e s wi t h t h e p o p u l a t i o n o f t h e s u r ve y a r e a , r a n gi n g fr o m 2 0 pe r c e n t i n a r e a s wi t h a p o p u l a t i o n l e s s t h a n 5 0 , 0 0 0 t o 4 p e r c e n t i n a r e a s wi t h o ve r 1 mi l l i o n . H o me i n t e r vi e ws wi l l u s u a l l y b e p r e fe r r e d o ve r o i l i e r h o u s e h o l d s u r ve y me t h o d s i f a l o n g o r c o m p l i c a t e d s u r ve y i n s t r u me n t i s t o b e u s e d . H i gh e r re s p o n s e r a t e s ma y b e e xp e c t e d i n h o m e i n t e r vi e w s u r ve ys t h a n i n t e l e p h o n e o r ma i l s u r ve ys . O n t h e o t h e r h a n d , h o m e i n t e r vi e w s u r ve ys a r e u s u a l l y mo r e e xp e n s i ve t h a n o t h e r m e t h o d s . D i R e n z o (11) r e p o r t e d t h a t t h e c o s t s o f i n t e r vi e wi n g a n d fi e l d wo r k fo r t h r e e h o m e i n t e r vi e w s u r ve ys ra n ge d , i n 1 9 7 4 d o l l a r s , fr o m $ 1 0 . 0 9 t o $ 2 3. 7 9 p e r c o mp l e t e d i n t e r vi e w. He r e p o r t e d t h a t t h e c o s t s o f t e l e p h o n e a n d m a i l s u r ve ys we r e $ 11. 0 7 a n d $ 4. 2 5 ( 1 9 7 4 d o l l a r s ) p e r c o m p l e t e d i n t e r vi e w, r e s pe c t i ve l y. S u c h s u r ve ys t yp i c a l l y h a ve l o we r r e s p o n s e r a t e s a n d r e q u i r e gr e a t e r c a r e i n t h e i r d e s i gn a n d s u p e r vi s i o n t o a vo i d u n d e r r e p o r t i n g o f t r i p s a n d t he i n t r o d u c t i o n o f b i a s e s. The roadside survey method Th i s me t h o d c o n s i s t s o f s t o p p i n g ve h i c l e s a n d a s ki n g t h e d r i ve r s fo r i n fo r ma t i o n o n t r i p o r i gi n , d e s t i n a t i o n, an d p u r p o s e. Typ i c a l l y, a l l o f t h e ve h i c l e s p a s s i n g t h e r oa d s i d e s u r ve y s t a t i o n a r e c o u n t e d , b u t o n l y a s a mp l e o f t h e d r i ve r s ( e . g. , 2 0 p e r c e n t ) a re i n t e r vi e w'e d . Al t e r n a t i ve r o a d s i de s u r ve y me t h o d s i n vo l ve h a n d i n g o u t vo l u n t a r y r e t u r n p o s t c a r d q ue s t i o n n a i r e s t o d r i ve r s o r r e c o r d i n g l i c e n s e n u m b e r s a n d m a i l i n g q u e s t i o n n a i r e s t o t h e ve h i c l e o wn e r s . 'Th e s t a t i o n s wh e r e t h e c o u n t s a r e m a d e a r e u s ua l l y l oc a t e d o n a l l t h e ma i n a p p r o a c h h i gh wa ys t o t h e s u r ve y a r e a. If t he s t a t i o n s a r e l o c a t e d a l o n g a n i ma gi n a r y l i n e e n c i r c l i n g a s u r ve y a r e a, t h e y a r e r e fe r r e d t o a s “c o r d o n s t a t i o n s, ” a n d t h e c o u n t s a r e kn o wn a s “c o r d o n c o u n t s. ” R o a d s i d e s u r ve ys a r e a l s o u s e d t o i n t e r c e p t a n d i n t e r vi e w d r i ve r s o f ve h i c l e s cr o s s i n g s e l e c t e d b o u n d a r y l i n e s ( i . e . , s c re e n l i n e s ) w'i t h i n a s ta t e o r r e gi o n . R o a d s i d e s u r ve ys a r e e s p e c i a l l y u s e fu l i n r e c o r d i n g re l a t i ve l y l o n g a n d i n fr e q u e n t t r i p s , i n c l u d i n g t h o se ma d e b y p e r s o n s wh o r e s i d e o u t s i d e t h e s u r ve y a r e a . S u c h s u r ve ys p r o vi d e o n l y l i mi t e d i n fo r ma t i o n a b o u t t h e n a t u r e o f t h e t r i p s s u r ve ye d a n d p r a c t i c a l l y n o t i l i n g a b o u t t h e s oc i a l a n d e c o n o m i c c ha r a c t e r i s t i c s o f t h e t r i p ma ke r. R o a d s i d e s u r ve ys mu s t b e c a r e fu l l y p l a n n e d a n d e xe c u t e d t o p r e ve n t i n t o l e r a b l e c o n ge s t i o n , e s p e c i a l l y a l o n g h e a vi l y t r a v e l e d r o u t e s.

146 T R A N S P O RTATI O N P L A N N I N G

Modal surveys In a l a rge n u mb e r o f s t a t e s wh e r e mu l t i mo d a l t r a n s p o r t a t i o n a ge n c i e s h a ve b e e n e s t a b l i s h e d , s p e c i a l s u r ve ys ma y h a ve t o be ma d e o f t r a ve l b y b u s , r a i l , a n d a i r t r a n s p o r t a t i o n. Typ i c a l l y, mo d a l s u r ve ys a r e m a d e b y i n t e r vi e wi n g p a s s e n ge r s a l t e r mi n a l s o r wh i l e o n b o a r d p u b l i c c a r r i e r s . To a l e s s e r e xt e n t , te l e p h o n e i n t e r vi e ws a n d s u r ve ys o f l i c e n s e p l a t e s a t t e r m i n a l s h a ve b e e n u s e d t o c o l l e c t mo d a l t r a ve l d a t a. Th e U. S . D e p a r t m e n t , o f'Tra n s p o r t a t i o n h a s p u b l i s he d d e t a i l e d gu i d e l i n e s o n s t a t e wi d e m o d a l s u r ve ys (J 1) a n d u r b a n ma s s t r a n s p o r t a t i o n t r a ve l s u r ve ys ( 7 2 ) t o wh i c h t h e r e a d e r s h o u l d r e fe r fo r a d d i t i o n a l i n fo r ma t i o n . Goods transportation surveys Th e t r a n s p o r t a t i o n o f go o d s wi t h i n a s t a t e o r u r b a n a r e a i s c o m p l e x, i n vo l vi n g s e ve r a l t r a n s p o r t mo d e s , a c o mb i n a t i o n o f l i n e - h a u l a n d d i s t r i b u t i o n t ra ffi c , a n d a va r i e t y o f c o mmo d i t y t yp e s a n d u s e r s . Th e i m p a c t o f go o d s mo ve m e n t o n t h e fu n c t i o n i n g o f a t r a n s p o r t a t i o n s ys t e m i s s i gn i fi c a n t , a n d p l a n n e r s s h o u l d e n d e a vo r t o i n c o r p o r a t e go o d s t r a n s p o r t a t i o n p l a n n i n g i n t o t h e e xi s t i n g p l a n n i n g p r o c e s s . U n fo r t u n a t e l y, p l a n n i n g p r o c e d u r e s fo r go o d s t r a n s p o r t a n a l ys e s h a ve n o t ke p t pa c e wi t h t h o s e fo r p a s s e n ge r t ra n s p o r t a t i o n . B e c a u s e o f t h e c o m p e t i t i ve n a t u r e o f t h e fr e i gh t i n d u s t r y, fr e i gh t c a r r i e r s m a y h e re l u c t a n t , t o r e s p o n d t o ma i l e d q u e s t i o n n a i r e s. Tor t h i s r e a s o n , e xp e r i e n c e s u g ge s t s t h a t t i n e p e r s o n a l vi s i t — i n t e r vi e w t e c h n i q u e i s t h e m o s t e ffe c t i ve m e a n s o f ga t h e r i n g c o n fi d e n t i a l i n fo r ma t i o n fr o m transportation industry sources. In c e r t a i n i n s t a n c e s, go o d s t r a n s p o r t a t i o n s u r ve ys ma y h e l i mi t e d t o t h e c o l l e c t i o n o f o r i gi n “d e s t i n a t i o n i n fo r ma t i o n fo r t r u c ks b y t r u c kl o a d t yp e a n d we i g h t . O n t h e o t he r h a n d , c o mp r e h e n s i ve mu l t i mo d a l go o d s t r a n s p o r t a t i o n s u r ve ys ma y b e d e s i r e d i n wh i c h d e t a i l e d s h i p p i n g i n fo r m a t i o n i s s o u gh t fo r s p e c i fi c c o m mo d i t i e s , i n c l u d i n g c o n s i gn e e , s h i p p e r, c a r r i e r, c o m m o d i t y t yp e , o r i gi n , d e s t i n a t i o n, we i g h t , va l u e , t i me o f o r i gi n a n d d e s t i n a t i o n , a n d s h i p p i n g ra t e . It ma y b e p o s s i b l e t o c o l l e c t a gr e a t d e a l o f t e r m i n a l fa c i l i t y d a t a o n a c o n fi d e n t i a l b a s i s fr o m t e r mi n a l o p e r a t o r s , i n c l u d i n g t he n u mb e r o f mo ve me n t s p e r d a y ( b y mo d e t yp e ) a n d t h e c l a s s a n d vo l u m e o f ca rgo h a n d l e d d u r i n g a ve r a ge a n d p ea k p e r i o d s. A d d i t i o n a l i n fo r m a t i o n o n go o d s t r a n s p o r t a t i o n s u r ve ys i s gi ve n b y R e f. 13. Urban travel surveys B e fo r e d e s c r i b i n g t he a n a l ys i s o f s ys t e m s p la n n i n g d a t a , l e t . u s l o o k a t h o w t h e va r i o u s d a t a c o l le c t i o n p r o c e d u r e s d e s c r i b e d a b o ve m i gh t b e e m p l o ye d i n a n u r b a n o r i gi n - d e s t i n a t i o n ( O — D ) s u r ve y. O n e o f t h e fi r s t s t e p s i n p e r fo r mi n g a n u r b a n O — D s u r ve y i s t o d i vi d e t h e ge o gr a p h i c a r e a u n d e r s t u d y i n t o c o n ve n i e n t p la n n i n g u n i t s. It i s n e c e s s a r y t o e s t a b l i s h t h e l o c a t i o n o f t h e e xt e r n a l c o r d o n b o u n da r y, a n i ma gi n a r y l i n e e n c i r c l i n g t h e s u r ve y a r e a t h a t s e pa r a t e s t h e external area fr o m t h e internal area. 'T h e e xt e r n a l c o r d o n l i n e wi l l n o r ma l l y e nc o mp a s s e n t i r e p o l i t i c a l j u r i s d i c t i o n s , t h a t i s, t o wn s , c i t i e s, ce n s u s t r a c t s, a n d s o fo r t h , a n d t h e “ u r b a n i z e d a r e a ” a s d e fi n e d b y a ge n c i e s s u c h a s t h e B u r e a u o f t h e C e n s u s a n d t h e F e d e r a l H i gh wa y Ad mi n i s t r a t i o n .

Systems Planning 147 T h e i n t e r n a l a r e a i s s u b d i vi d e d i n t o a na l ys i s zo n e s . Th e b o u n d a r i e s o f t h e s e z o n e s s h o u l d, wh e n e v e r fe a s i b l e , co i n c i d e wi t h c e n s u s t r a c t b o u n d a r i e s a n d wi l l ge n e r a l l y fo l l o w e xi s t i n g s t r e e t s a n d h i gh wa ys . Th e z o n e s s h o u l d b e s m a l l e n o u gh t o a vo i d i n c l u s i o n o f a l a rge n u mb e r o f i n t r a z o n a l t r i p s. Th e F H V VA (14) . s u g ge s t s t h a t i n t r a z o n a l t r i p s s h o u l d c o mp r i s e n o t mo r e t h a n 1 0 t o 1 5 p e r c e n t o f t h e t o t a l t r i p s , 'f 'h e z o ne s a r e ge n e r a l l y s ys t e ma t i c a l l y n u m b e r e d t o fa c i l i t a t e c o d i n g a n d a n a l ys i s o f t r a ve l d a ta d u r i n g t h e a n a l ys i s p h a s e . C o m p r e h e n s i ve u r b a n 0 — 1 ) s t u d ie s u s u a l l y i n vo l ve t h e u s e o f a c o m b i n a t i o n o f t h e s u r ve y p r o c e d u r e s d e s c r i b e d p r e vi o u s l y: h o u s e h o l d t r a ve l s u r ve ys , r o a d s i de s u r ve ys , mo d a l s u r ve ys , a n d go o d s mo ve m e n t s u r ve ys . S u c h s u r ve ys c o n s i s t o f t wo p a r t s : 1 . An e xt e r n a l s u r ve y i n vo l vi n g t he c o l l e c t i o n o f t r a ve l d a t a o n ve h i c l e s c r o s s i n g t h e e xt e r n a l c o r d o n l i n e. 2 . An i n t e r n a l s u r ve y t h a t fo c u s e s o n t h e t r a ve l h a b i t s o f p e r s o n s wh o l i ve wi t h i n t h e a re a b o u n d e d b y t h e e xt e r n a l co r d o n l i n e. 'T h e e xt e r n a l s u r ve y d a t a a r e c o l l e c t e d al o n g t h e e xt e r n a l c o r d o n l i n e. D i r e c t i o n a l t ra ffi c c o u n t s a r e n o r ma l l y o b t a i n e d fo r e ve r y s t r e e t a n d h i gh wa y t h a t c r o s s e s t he c o r d o n l i n e . O r i gi n — d e s t i n a t i o n d a t a a r e c o l l e c t e d b y r o a d s i d e s u r ve ys p e r fo r me d o n a l l ma j o r r o u t e s t h a t c r o s s t h e cordon line. T h e i n t e r na l s u r ve y c o n s i s t s o f t h e fo l l o wi n g s u b d i vi s i o n s : ( 1 ) h o me i n t e r vi e ws ( t r i p s b y a l l i n d i vi d u a l s ) , ( 2 ) t r uc k s t u d i e s , ( 3 ) t a xi s t u d i e s, a n d ( 4 ) p u b l i c t r a n s i t i n fo r m a t i o n . In t e r v i e ws a r e m a d e o n a p r e d e t e r mi n e d sc h e d u l e a n d fo r ms a r e p r o vi d e d fo r t a b u l a t i n g t h e n e c e s s a r y i n fo r ma t i o n . 'Th e i n fo r ma t i o n r e q u i re d i s fo r t h e d a y p r e c e d i n g t h e h o me i n t e r vi e w. Th i s i n fo r ma t i o n i n c l u d e s t h e n u m b e r o f o c c u p a n t s i n a h o u se h o l d , o c c u p a t i o n , n u mb e r ma ki n g t h e t r i p, u s e o f p r i va t e o r p u b l i c t r a n s p o r t a t i o n, o r i gi n a n d d e s t i n a t i o n , p u r p o s e o f t h e t r i p, a n d s o fo r t h . In s e l e c t i n g t h e s a mp l e , u s e i s ma d e o f c e r t a i n a va i l a b l e b a s i c r e c o r d s . 'T h e s e m a y i n c l u d e ( 1 ) S a n b o r n ma p s , a s e r i e s o f c o p yr i gh t e d m a p s p r e p a r e d fo r t h e u s e o f i n s u r a n c e c o mp a n i e s , a s s e s s o r s, a n d s o fo r t h , wh i c h s h o w a i l s t r u c t u re s t o ge t h e r wi t h o t h e r i n fo r ma t i o n ; ( 2 ) c i t y d i r e c t o r i e s ; ( 3 ) B u r e a u o f t h e C e n s u s “B l o c k S t a t i s t i c s, ” wh i c h s h o w b l o c ks a n d b l o c k n u m b e r s ; a n d ( 4 ) l a n d - u s e ma p s t h a t ma y b e a va i l a b l e . Tru c k a n d t a xi i n fo r ma t i o n i s ge n e r a l l y a va i l a b l e fr o m t he r e c o r d s o f t h e c o m p a n i e s t h a t , o p e r a t e t h e m. U s u a l l y 2 0 p e r ce n t o f t he t r u c ks a n d 5 0 t o 1 0 0 p e r c e n t o f t h e t a xi s r e gi s t e r e d i n a n a re a a r e s a mp l e d . P u b l i c t r a n s i t i n fo r m a t i o n i s u s u a l l y o b t a i n e d d i r e c t l y fr o m t h e t r a n s i t c o mp a n i e s . Th i s s h o u l d i n c l u d e l o c a t i o n o f e xi s t i n g r o u t e s , s c h e d u l e o f o p e r a t i o n s , a n d t h e t o t a l n u m b e r o f p a s s e n ge r s c a r r i e d o n a n a ve r a ge we e k d a y d u r i n g t h e p e r i o d o f t h e s u r ve y. 'T h e c o m p l e t e n e s s wi t h wh i c h t r i p s a r e r e p o r t e d i n t h e i n t e r n a l s u r ve y

148 T R A N S P O RTATI O N P L A N N I N G

m a y b e c h e c ke d b y t h r e e me t h o d s : ( 1 ) u s e o f c o n t r o l p o i n t s fo r c o mp a r i s o n , ( 2 ) a s c r e e n - l i n e c o m p a r i s o n , a n d ( 3 ) a c o r d o n - l i ne c o mp a r i s o n . N o t mo r e t h a n t h r e e o r fo u r c o n t r o l p o i n t s s h o u l d be s e l e c t e d fo r u s e i n a n y o n e s t u d y. C o n t r o l p o i n t s a r e u s u a l l y vi a d u c t s , b r i d ge s , u n d e r pa s s e s , o r o t h e r p o i n t s o f c o n s t r i c t i o n t h r o u gh wh i c h l a rge vo l u me s o f t r a ffi c p a s s . Th e a ve r a ge t r a ffi c vo l u m e a n d c l a s s i fi c a t i o n a t e a c h c o n t r o l p o i n t mu s t b e d e t e r m i n e d b y m a n u a l c o u n t s ma d e d u r i n g t h e s u r ve y s o t h a t t h e e xp a n d e d c o u n t s o b t a i n e d fr o m h o me i n t e r vi e ws ca n b e c o mp a r e d wi t h t h e ac t u a l gr o u n d c o u n t s a t t h e se p o i n t s. S c r e e n i i n e s a r e n a t u r a l b a r r i e r s s u c h a s r i ve r s o r r a i l r o a d s ; t h e y u s u a l l y h a ve a l i m i t e d n u mb e r o f c r o s s i n gs at wh i c h gr o u n d c o u n t s c a n b e m a d e a t a m i n i m u m e xp e n s e . 'Th e p u r p o s e o f t h e s c r e e n l i n e i s t o d i vi d e t h e a r e a o f t he i n t e r n a l s u r ve y i n t o t wo p a r t s i n o r d e r t o d e te r mi n e t h e n u m b e r o f ve h i c l e s m o vi n g fr o m o n e p a r t t o t h e o t h e r. A co mp a r i s o n c a n t h e n b e m a d e b e t we e n t h e n u mb e r o f t r i p s h a vi n g t h e i r o r i gi n o n o n e s i de a n d d e s t i n a t i o n o n t he o t h e r, a s ac t u a l l y c o u n t e d, a n d t h e n u mb e r o f t r i p s a s d e t e r m i n e d fr o m t h e e xp a n d e d i n t e r vi e ws . A c o r d o n - l i n e c o m p a r i s o n de a l s wi t h p a s s e n ge r -c a r t r i p s b y r e s i d e n t s o f t h e i n t e r n a l a r e a a n d t r u c k t r i p s b y t r u c ks r e gi s t e r e d i n t h e a r e a , b u t o n l y t h o s e t r i p s wh i c h c r o s s t h e c o r d o n l i n e. Th e t o ta l n u mb e r o f s uc h t r i p s r e c o r d e d i n t h e e xt e r n a l s u r ve y c a n be c o mp a r e d wi t h t h e t o t a l n u mb e r r e c o r d e d i n t h e i n t e r n a l s u r ve y. In m a n y r e c e n t s u r ve ys c o n d u c t e d i n va r i o u s mu n i c i p a l i t i e s b y t h e m e t h o d j u s t d e s c r i b e d , a b o u t 9 0 p e r c e n t o f t h e t r a ffi c p a s s i n g co n t r o l p o i n t s a n d s c r e e n l i n e s d u r i n g 1 6 h r o f o p e r a t i o n o f e xt e r n a l s t a t i o n s ha s b e e n a c c o u n t e d fo r b y t h e e xp a n d e d i n t e r vi e w d a t a . 'T h e r e ma i n i n g 1 0 p e r c e n t ha s b e e n a s s u m e d t o b e ma d e u p o f c a r s c i r c u l a t i n g i n s e a r c h o f a p a r ki n g p l a c e , o f u n i m p o r t a n t s h o r t t r i p s n o t re p o r t e d i n i n t e r vi e ws , a n d o f t r i p s b y p e r s o n s l i vi n g o u t s i d e t h e a r e a a n d n o t i n t e r c e p t e d a t d i e e xt e r n a l c o r d o n s t a t i o n s. Th e s e t r i p s a r e c o n s i d e r e d t o b e o f mi n o r i mp o r t a n c e a s fa r a s t h e p r i n c i pa l p u r p o s e s o f t h e s u r ve y a r e c o n c e r n e d. F i gu r e 6 - 3 s h o ws a c o mp a r i s o n o f t h e n u mb e r o f ve h i c l e s c o u n t e d a t c o n t r o l p o i n t s wi t h t h e n u mb e r p a s s i n g t h o s e p o i n t s a s d e t e r mi n e d fr o m t h e i n t e r vi e ws .

600 0

600 0 500 0 400 0 300 0 2000

1000

9-10 1011 A.M.

FIGURE 6-3 Baltimore travel habit .survey. Comparison of traffic passing three control points as reproduced from interviews and as actually counted at those points. (Courtesy Federal Highway Administration.)

Systems Planning 149 F o r c i t i e s wi t h a p o p u l a t i o n o f l e s s t h a n 5 0 0 0 i t ma y n o t b e n e c e s s a r y t o c o n d u c t a n i n t e r n a l s u r ve y, II ma y b e p o s s i b le t o c o l l e c t s u ffi c i e n t O D i n fo r m a t i o n b y m e a n s o f r o a d s i d e i n t e r vi e ws a t t h e e xt e r n a l c o r d o n . In s l i gh t l y l a rge r c i t i e s ( wi t h p o p u l a t i o n s i n ( h e r a n ge o f 5, 0 0 0 t o 5 0 , 0 0 0, i n l i e u o f a n i n t e r n a l s u r ve y, r o a d wi s e s u r ve ys ma y b e p e r fo r m e d al o n g t wo c o r d o n l i n e s , o n e a t t h e e d ge o f t h e c i t y a n d o n e a t t h e fr i n ge o f t h e c e n t r a l business district. O r i gi n — d e s t i n a t i o n d a t a h a ve t r a d i t i o n a l l y b e e n d i s p la ye d i n t h e fo r m o f de s i r e l i n e m a p s . D e s i r e l i n e s i n d ic a t e t h e d e s i r e s o f ve h i c l e u s e r s a s d i r e c t l i n e s o f t r a ve l fr o m o n e p o i n t t o a n o t h e r wi t h i n a gi ve n a re a , a s s u m i n g t h a t d i r e c t r o u t e s a r e a va i l a b l e . Th e i n fo r ma t i o n t h a t t h e se l i n e s r e p r e s e n t i s e s p e c i a l l y h e l p fu l t o p l a n n i n g a n d d e s i gn en gi n e e r s wh e n r o u t e s fo r n e w a r t e r i a l i m p r o ve me n t s a r e t o be s e l e c t e d. P l a n s fo r i m p r o ve m e n t s h o u l d b e ke ye d t o t h e ma j o r d e ma n d s o f t r a ffi c , a s i n d i c a t e d b y t h e d e s i r e l i n e s h a vi n g t h e gr e a t e r wi d t h s i n a p l o t o f t h e t yp e s h o wn i n F i gu r e 6 - 4 . As s u mi n g t h a t t h i s c a n b e d o ne , t h e r o u t e s t h u s i m p r o ve d s h o u l d b e s t me e t t h e d e s i r e s o f t h e l a rge s t n u mb e r o f ve h i c l e users. Parking surveys 'T h e p u r p o s e o f a p a r ki n g s u r ve y i s t o d e t e r mi n e t h e p a r ki n g h a b i t s a n d r e q u i r e m e n t s o f m o t o r i s t s a n d t h e r e l a t i o n o f t h e s e fa c t o r s t o o t h e r u s e s o f e xi s t i n g p a r ki n g fa c i l i t i e s . A p a r ki n g s u r ve y s h o u l d b e d e s i gn e d s o t h a t , t h e i n fo r ma t i o n c o l l e c t e d wi l l p r o vi d e n e e d e d d a ta fo r t he e va l u a t i o n o f t h e s e ve r a l fa c t o r s i n t h e p a r ki n g p r o b l e m . Th e i n fo r ma t i o n s e c u r e d s h o u l d i n c l u de ( 1 ) t h e l o c a t i o n , ki n d , a n d c a p a c i t y o f e xi s t i n g p a r ki n g fa c i l i t i e s ; ( 2 ) t h e a mo u n t , o f p a r ki n g s p a c e ne e d e d t o s e r ve p r e se n t d e ma n d s ; ( 3 ) t h e a p p r o xi ma t e l o c a t i o n o f p o s s i b l e a d d i t i o n a l p a r ki n g fa c i l i t i e s ; a n d ( 4 ) t h e le ga l , a d m i n i s t r a t i ve , fi n a n c i a l , a n d e c o n o mi c a s p ec t s o f pa r ki n g fa t a l i t i e s . 'T h e fi r s t p ha s e o f t h e p a r ki n g s u r ve y i s t o ma ke a n i n ve n t o r y o f a l l a va i l a b l e p a r ki n g fa c i l i t i e s . Th i s i n c l u d e s c u r b a n d o ff- s t r ee t p a r ki n g a r e a s s uc h a s p a r ki n g l o t s, ga r a ge s , an d s e r vi c e s t a t i o n s . An y p h ys i c a l a n d l e ga l r e s t r i c t i o n s a r e a l s o t o b e n o t e d. Th e t h e o r e t i c a l c a p a c i t y o f a p a r ki n g l o t o r ga r a ge i s u s u a l l y d e t e r mi n e d b y d i vi d i n g t h e gr o s s a r e a b y t h e a re a n e e d e d b y o n e c a r, wh i c h va r i e s 1 Vo m a b o u I 2 5 6 t o 4 0 0 ft ", d e p e n d i n g o n t h e t y p e o f fa t : i i i t y a n d t h e d e s i gn . ( S e e C h a p t e r 9 . ) Twe n t y- t wo l i n e a l fe e l i s u s u a l l y u s e d i n de t e r mi n i n g t h e o r e t i ca l c u r b c a p a c i t i e s. C a l c u l a t i o n o f t h e t h e o re t i c a l c a p ac i t y d o e s n o t i mp l y mo r e c a r s c a n n o t b e a c c o m m o d a t e d . S o me c a r s a r e p a r ke d fo r s h o r t p e r i o d s o f t i m e , a n d t h e i r s p a c e t h e n b e c o me s a va i l a b l e t o o t h e r s. C o o p e r a t i o n o f t h e o wn e r s o f o ff- s t r e e t p a r ki n g fa c i l i t i e s mu s t Ir e o b t a i n e d i n o r d e r t o d e t e r m i n e t h e a c t u a l c a p a c i t ie s o r n u mb e r s o f ca r s t h a t a r e a c c o mm o d a t e d fo r p e r i o d s o f t h e s u r ve y s o t h a t t h e r e s u l t s c a n b e c o r r e la t e d wi t h c a p a c i t i e s o f o t h e r fa c i l i t i e s . Ad d i t i o n a l i n i o r ma t i o n o n t h e d u r a t i o n o f p a r ki n g i s a l s o t o b e o b t a i ne d ,

150 T R A N S P O RTATI O N P L A N N I N G

'T h e d e t e r m i n a t i o n o f a c t u a l c a p a c i t i e s o f c u r b p a r ki n g fa c i l i t i e s i s m o r e r e a d i l y d o n e . P a r ki n g, wh e n p e r mi t t e d , i s u s u a l l y fo r I - o r 2 - h r p e r i o d s . Th e r e fo r e , t h e n u mb e r o f s p a c e - h o u r s a va i l a b l e i s d e t e r mi n e d fr o m t h e i n ve n t o r y o f

148 TRAN SPOR TATIO N PLAN NING S flcms , >‘ ’,an"i"8 149

FIGURE 6-4 Comparison of traffic on actual routes (above) and desire lines (below) of' travel Cor Rome, Georgia. (Courtesy Georgia Department of 'Transportation.)

FIGURE 6-4 (rontinued)

150 TRANSPORTATION PLANNING t h e c u r b s p a c e a va i l a b l e . It i s a s s u me d ( h a t p a r ki n g i s fo r t h e l e ga l t i me s p e c i fi e d . S t u d i e s a re a l s o ma d e t o a s c e r t a i n t h e e xt e n t o fi l l e ga l p a r ki n g a n d i t s e ffe c t o n t h e t o t a l e ffe c t i ve c a p a c i t y o f c u r b p a r ki n g fa c i l i t i e s . In o r d e r t o d e t e r m i n e t h e n u mb e r o f c a r s t h a t ma y u t i l i z e a va i l a b l e p a r ki n g s p a c e s i n a c e n t r a l a re a , a c o r d o n l i n e i s u s u a l l y d r a wn ar o u n d t h e a r e a t o b e s t u d i e d a n d c o r d o n c o u n t s a r e ma d e o f a l l ve h i c l e s e n t e r i n g a n d l e a vi n g i t . Th e c o u n t s a r e ma d e ma n u a l l y s o t h a t a mo t o r - ve h i d e c l a s s i fi c a t i o n c a n b e m a d e . Au t o ma t i c r ec o r d e r s a r e o ft e n u s e d t o s u p p l e m e n t , t h e m a n u a l c o u n t s a n d t o s e r ve a s a b a s i s o f c o n t r o l fo r a b n o r m a l c o n d i t i o n s. M o t o r i s t s wh o a r e i n t e r vi e we d a t a l l p a r ki n g fa c i l i t i e s wi t h i n t h e c o r d o n a r e a a r e a s ke d fo r t h e i r h o me a d d re s s , d e s t i n a t i o n, a n d t h e p u r p o s e o f t h e t r i p . F i gu r e 6 - 5 s h o w’s t h e r e s u l t s o f a p a r ki n g s u r ve y i n t h e c i t y o f Baltimore. A p a r ki n g s u r ve y s h o u l d a l s o i n c l u de a s t u d y o f t he a r e a fo r fu r t h e r o ff- s t r e e t p a r ki n g fa c i l i t i e s . Th i s s h o u l d i n c l u d e t h e i n ve s t i ga t i o n o f va c a n t l o t s , o b s o l e t e b u i l d i n gs , a n d b l i gh t e d r e s i d e n t i a l o r b u s i n e s s a re a s wi t h i n t h e a r e a o f d i e p a r ki n g s u r ve y. Me n t i o n ma y be ma d e o f o t h e r p a r ki n g a r e a s o u t s i d e t h e l i m i t s o f t h e c e n t ra l s h o p p i n g a r e a t h a t ma y a l s o b e u se d . Th e s e a r e a s a r e u s u a l l y r e fe r r e d t o a s fr i n ge p a r ki n g ar e a s , t h e i d e a b e i n g t h a t m o t o r i s t s c a n p a r k n e a r t h e c e n t r a l b u s i n e s s d i s t r i c t a n d u s e a va i l a b l e ma s s t r a n s p o r t a t i o n fa c i l i t i e s a s a me a n s o f a r r i vi n g a t t h e i r d e s t i n a t i o n . M a n y m u n i c i p a l i t i e s h a ve t r i e d t h i s t yp e o f fa c i l i t y, b u t a s a ge n e r a l r u l e i t l i a s n o t p r o ve d a s s u c c e s s fu l a s d e s i r e d . In o r d e r t o b e p r o p e r l y e va l u a t e d , a p a r ki n g s u r ve y s h o u l d a l s o i n c l u d e a n i n ve n t o r y o f t h e s t a t e l a ws , l o c a l o r d i n a n c e s, a n d j u d i c i a l d e c i s i o n s p e r t a i n i n g t o p a r ki n g fa c i l i t i e s . Th i s s h o u l d i n d u d e p u b l i c r e gu l a t i o n s fo r t h e l i c e n s i n g o f co m me r c i a l o ff- s t r e e t p a r ki n g fa c i l i t i e s , c u r b r e s t r i c t i o n s, a n d p o l i c e r e gu l a t i o n s . A n i n ve s t i ga t i o n i n t o t h e a d mi n i s t r a t i o n o f p a r ki n g fa c i l i t i e s s h o u l d b e m a d e i n o r d e r t o d e t e r mi n e wh i c h s t a t e a n d l oc a l a ge n c i e s a r e r e s p o n s i b l e fo r t h e p l a n n i n g, l oc a t i o n , fi n a n c i n g, c o n s t r u c t i o n , o p e ra t i o n , a n d m a i n t e n a n c e o f p a r ki n g fa c i l i t i e s wi t h i n t h e mu n i c i p a l i t y t h a t i s be i n g s u r ve ye d . F o r e xa m p l e , i n a gi ve n mu n i c i p a l i t y t h e p o l i c e ma y h a ve d i e r e s p o n s i b i l i t y fo r e n fo r c i n g c u r fr p a r ki n g r e s t r i c t i o n s, u : h i l e a t r a ffi c c o m m i s s i o n m a y h a ve t h e a u t h o r i t y t o e s t a b l i s h s u c h p a r ki n g r e gu l a t i o n s , i n c l u d i n g m e t e r p a r ki n g. Th e z o n i n g c o m mi s s i o n ma y r e q u i r e p a r ki n g p r o vi s i o n s u n d e r z o n i n g l a ws fo r va r i o u s p r o p e r t y u s e s. Al l a d mi n i s t r a t i ve fa c t s s h o u l d b e i n c l u de d s o t h a t i n t h e f i n a l a n a l ys i s r e c o m me n d a t i o n s ma y l i e m a d e t o r e m e d y a n y d e fi c i e n c i e s t h a t ma y e xi s t . In m a t t e r s p e r t a i n i n g t o t h e fi n a n c i n g o f p a r ki n g s e r vi c e s , s t u d i e s s h o u l d i n c l u d e t h e a ggr e ga t e r e ve n u e fr o m p a r ki n g me t e r s a n d i t s d i s p o s i t i o n a s we l l a s t h e a s s i gn me n t o f c o s t s o f p a r ki n g fa c i l i t i e s fo r o ffs t r e e t p a r ki n g a c c o r d i n g t o t h e b e n e fi t 's r e c e i ve d . B e ne fi t s ma y b e a p p o r t i o n e d t o p r o p e r l y o wn e r s , b u s i ne s s e s t a b l i s h me n t s , t h e mo t o r i s t s , t h e ge n e r a l c o m m u n i t y, a n d t h e mu n i c i p a l i t y i t s e l f. T h e i n fo r m a t i o n r e c e i ve d i n a p a r ki n g s u r ve y ma y p o i n t t o a n u mb e r o f r e c o m m e n d a t i o n s fo r t h e r e l i e f o f c o n ge s t i o n a n d fo r ge n e r a l

i m p r o ve m e n t i n t r a ffi c fa c i l i t i e s . S u c h r e c o m me n d a t i o n s mi gh t , fo r S ys t e m s P l a n n i n g 151 e xa m p l e , i n c l u d e t h e p r o vi -

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154 TRANSPORTATION PLANNING

s i o n o f a d d i t i o n a l p a r ki n g fa c i l i t i e s , e i t h e r p u b l i c l y o r p r i va t e l y o wn e d , b e t t e r e n fo r c e m e n t o f p a r ki n g r e gu l a t i o n s t o ma ke a va i l a b l e s p a c e a t . t h e c u r b n o w b e i n g u s e d b y mo t o r i s t s p a r ki n g i l l e ga l l y, c h a n ge s i n z o n i n g r e gu l a t i o n s , a n d s o fo r t h .

6-6 Data analysis B e c a u se o f t he m a gn i t u d e a n d c h a n gi n g n a t u r e o f t h e p r o b l e m, i t i s d i ffi c u l t t o p r e p a r e a n a c c u r a te u p - t o - d a t e i n ve n t o r y o f a n e xi s t i n g t r a n s p o r t a t i o n s ys t e m a n d t h e t ra ffi c i t s e r ve s . It i s e ve n mo r e d i ffi c u l t t o a c c u ra t e l y fo r e c a s t fu t u r e t r a ffi c t h a t wi l l u se a p r o p o s e d t r a n s p o r t a t i o n s ys t e m . Tra n s p o r t a t i o n p l a n n e r s fa c e t h e c h a l le n ge o f ma ki n g r e l i a b l e fo r e c a s t s o f t r a ffi c d e m a n d t h a t r e fl e c t t h e e ffe c t s o f c h a n ge s i n p o p u l a t i o n a n d s o c i a l a n d e c o n o m i c c o n d i t i o n s a s we l l a s c h a n ge s i n t h e p h ys i c a l t r a n s p o r t s ys t e m , U n l e s s r e l i a b le fo r e c a s t s o f fu t u r e t r a ffi c a r e ma d e , t r a n s p o r t a t i o n o ffi c i a l s fa c e t h e r i s k o f b u i l d i n g fa c i l i t i e s t h a t wi l l ei t h e r r e c e i ve l i t t l e u s e o r b e p r e m a t u r e l y o ve r l o a d e d . Tra n s p o r t a t i o n p l a n n e r s h a ve d e ve l o p e d me t h o d o l o gi e s d e s i gn e d t o fo r e c a s t t r a ffi c d e m a n d fo r a gi ve n r o u t e o r c o r r i d o r a s we l l a s fo r a n e n t i r e t r a n s p o r t a t i o n s ys t e m ( n e t wo r k) . T h e t r a d i t i o n a l a p p r o a c h , e mp l o ye d p r i n c i p a l l y fo r r u r a l fa c i l i t i e s , h a s b e e n t o fo r e c a s t t r a ffi c fo r a s p e c i fi c h i gh wa y s e c t i o n b y s u b d i vi d i n g t h e t r a ffi c i n t o i t s va r i o u s c o mp o n e n t s a n d t o ma ke s e p a ra t e p r o j e c t i o n s fo r e a c h c o m p o n e n t . Th e r e c o gn i z e d c o mp o n e n t s o f fu t u r e t ra ffi c fo r a n e w o r i m p r o ve d fa c i l i t y i n c l u d e : 1. Existing traffic. Tra ffi c c u r r e n t l y u s i n g a n e xi s t i n g h i gh wa y t h a t i s t o b e i m p r o ve d , 2. Normal traffic growth. Tra ffi c t h a t c a n b e e xp l a i n e d b y a n t i c i pa t e d gr o wt h i n s l a t e o r r e gi o n a l p o p u l a t i o n o r b y a r e a wi d e c h a n ge s i n l a n d use, 3. Diverted traffic. Tra ffi c t h a t : s wi t c h e s t o a n e w fa c i l i t y fr o m n e a r b y r o a d wa ys . 4. Converted traffic. Tra ffi c c h a n ge s r e s u l t i n g fr o m ch a n ge o f mo d e . 5. Change of destination traffic. Tra ffi c t h a t l i a s c h a n ge d t o d i ffe r e n t d e s t i n a t i o n s, wh e r e s u c h c h a n ge i s a t t r i b u t a b le t o t h e a t t r a c t i ve n e s s o f t h e i m p r o ve d t r a n s p o r t a t i o n a n d n o t t o c h a n ge s i n l a n d u s e. 6. Development traffic. Tra ffi c d u e t o i mp r o ve m e n t s o n a d j a c e n t l a n d i n a d d i t i o n t o t h e d e ve l o p me n t t h a t wo u l d h a ve t a ke n p l a c e h a d t h e n e w o r i m p r o ve d h i gh wa y n o t b e e n c o n s t r u c t e d. 7. Induced traffic. Tra ffi c t h a t d i d n o t p r e vi o u s l y e xi s t i n an y fo r m, b u t r e s u l t s wh e n n e w o r i m p r o ve d t r a n s p o r t a t i o n fa c i l i t i e s a r e p r o vi d e d . In r e c e n t ye a r s , p l a n n e r s h a ve d e ve l o p e d me t h o d o l o gi e s fo r e s t i m a t i n g t h e d i s t r i b u t i o n o f fu t u r e t r a ffi c o ve r a n e n t i r e t r a n s p o r t a t i o n n e t wo r k. Th e s e p r o c e d u r e s , wh i c h h a ve b e e n u s e d fo r b o t h u r b a n a n d s t a t e wi d e ( 5 ) s ys t e m s , i n vo l ve t h e u s e o f c o mp u t e r s i mu l a t i o n p r o gr a ms , c o m p r i s e d t yp i c a l l y o f fi ve t yp e s o f mo d e l s : 1. L a n d u s e . 2. Tri p ge n e r a t i o n .

S y s t e m s P l a n n i n g 155

3. 4. 5.

Tri p d i s t r i b u t i o n. Tra ffi c a s s i gn m e n t . Modal split.

T h e m o d e l s a re m a t h e m a t i c a l e q u a t i o n s an d p r o c e d u r e s t h a t c o l le c t i ve l y r e l a t e t r a ve l p a t t e r n s t o l a n d u s e , d e mo g r a p h i c c h a r a c t e r i s t i c s, a n d p a r a m e t e r s o f t h e t ra n s p o r t a t i o n s ys t e m. Th e mo d e l s a r e d e ve l o p e d a n d “ c a l i b r a t e d ” fo r a gi ve n s t u d y a r e a s o a s t o re p r o d u c e e xi s t i n g t r a ve l p a t t e r n s a s de t e r m i n e d fr o m ac t u a l c o u n t s, As s u mi n g t h e b a s i c r e l a t i o n s h i p s b e t we e n t r a ve l , l a n d u s e, a n d s o c i o e c o n o mi c c ha r a c t e r i s t i c s r e m a i n c o n s t a n t o ve r t i m e , p l a n n e r s u s e t h e mo d e l s t o e va l u a t e fu t u r e a l t e r n a t i ve l a n d u s e a n d t r a n s p o r t a t i o n s ys t e ms .

Land-use models “ T h e l a n d u se m o d e l i s a p r o c e d u r e wh i c h e s t i ma t e s fu t u r e d e ve l o p m e n t b y a n a l ys i s z o n e. Th e s e es t i ma t e s i n c l u d e n o t o n l y l a n d u s e per se, b u t a l s o e s t i m a t e s o f t h e s oc i o e c o n o mi c va r i a b l e s wh i c h a r e u s e d i n t h e t r i p ge n e r a t i o n m o d e l s , s u c h a s p o p u l a t i o n, d we l l i n g u n i t s , a u t o o w n e r s h i p, i n c o m e , e m p l o y m e n t , r e t a i l s a l e s, e t c . ” ( 7 5 ). S u c h e s t i ma t e s a r e n o r m a l l y m a d e b y e c o n o mi c o r d e mo gr a p h i c p la n n e r s r a t h e r t h a n b y h i gh wa y o r t r a n s p o r t a t i o n s p e c i a l i s t s.

Trip generation models Tri p ge n e r a t i o n m o d e l s p r o vi d e a me a s u r e o f t h e r a t e o f t r i p - ma ki n g fo r e a c h a na l ys i s z o n e . Tri p ge n e r a t i o n r a l e s, wh i c h va r y wi t h t r i p p u r p o s e , a r e n o r m a l l y e xp r e s s e d a s a fu n c t i o n o f l a n d - u s e a n d d e mo gr a p h i c p a r a m e t e r s . S t u d i e s h a ve s h o wn t h a t, wi t h i n a n u r b a n a r e a, t r i p ge n e r a t i o n va l u e s a r e m o s t c l o s e l y r e l a t e d t o t h r e e ch a r a c t e r i s t i c s o f l a n d u se : ( 1 ) i n t e n s i t y o f l a n d u s e ( d we l l i n g u n i t s p e r a c r e, e mp l o ye e s p e r ac r e , e t c . ) ; ( 2 ) c h a r a c t e r o f l a n d u s e ( e . g. , a ve r a ge fa mi l y i nc o me , c a r o wn e r s h i p ) ; a n d ( 3 ) l o c a t i o n r e l a t i ve t o t h e c i t y c e n t e r. Tri p ge n e r a t i o n r e l a t i o n s h i p s “u s u a l l y t a ke t h e fo r m o f ma t h e ma t i c a l e q u a t i o n s o f s e ve r a l i n d e p e n d e n t, va r i a b l e 's , o r t a b l e s t h a t c l a s s i f y ea c h z o n e o r d we l l i n g u n i t a c c o r d i n g t o i t s c h a r a c t e r i s t i c s a n d gi ve t h e n u mb e r o f t r i p s wh i c h m a y b e e xp e c t e d t o Ir e gi n a n d e n d a t t h e z o n e o r d we l l i n g u n i t ( t r i p e n d s ) ” ( 7 . 5 ). A n e xa m p l e o f t h e p r o ce d u r e u s e d i n e s t i ma t i n g t r i p s p r o d u c e d b y a r e s i d e n t i a l z o n e i s s h o wn a s fi gu r e 6 - 6 .

Trip distribution models Tri p d i s t r i b u t i o n m o d e l s be gi n wi t h t h e n u mb e r o f t r i p e n d s ge n e r a t e d b y e a c h z o n e a n d a n s we r t h e q u e s t i o n, ‘ ’ W h a t , z o ne a r e t h e t r i p s go i n g t o a n d c o m i n g fr o m ? ” S e ve r a l t r i p d i s t r i b u t i o n mo d e l s h a ve b e e n d e s c r i b e d i n ( l i e l i t e r a t u r e , b u t o n l y t wo o f t h e mo s t p r o mi n e n t mo d e l s wi l l b e d e s c r i b e d h e r e — t h e gr a vi t y mo d e l a n d t h e F r a t a r me t h o d . The gravity model Th e gr a vi t y mo d e l i s s o n a me d b e c a u s e o f i t s s i mi l a r i t y t o N e wt o n ’s l a w o f gr a vi t a t i o n . E mp l o ye d fi r s t fo r s o c i o l o gi c a l a n d ma r ke t i n g

156 TRANSPORTATION PLANNING

r e s e a rc h , t h e gr a vi t y m o d e l b e ga n t o b e u s e d fo r t r a n s p o r ta t i o n s t u d i e s i n t h e e a r l y 1 9 5 0 s. S i n c e t h a t t i me , t h e mo d e l h a s b e e n s l i gh t l y mo d i fi e d a n d has

Systems Planning

157

INPUT: DWELLING UNITS AND INCOME CURVE A. PERCENT DWELLING UNiTS BY INCOME & CAR OWNERSHIP DISTRIBUTION , ENTER CURVE WITH INCOME TO DETERMINE PERCENT OF DWELLING UNITS WITH 0.1,2 3 OR MORE AUTOSMULTIPLY BY NUMBER OF DWELLING UNI fS TO OBTAIN NUMBER OF HOUSEHOLDS BY OWNERSHIP CLASS.

INCOME ($) DATA FOR CURVES FROM0-0 SURVEY,CENSUS STANDARD TRANSPORTATION PACKAGE OR "BORROWED" FROM ANOTHER STUDY AREA

CURVE B. TRIPS PER DWELLING UNIT BY INCOME & CAR OWNERSHIP . ENTER CURVE WITH INCOME AND NUMBER OF DWELLING UNITS WITH 0.1 2. & 3 OR MORE AUTOS TO DETERMINE THE PERSON TRIP RATE PER DWELLING UNIT, MULTIPLY THE RATE BY NUMBER OF HOUSEHOLDS TO OBTAIN TRIPS PRODUCED.

INCOME [$) DATA FOR CURVES FROM O D SURVEY OR "BORROWED':

CURVE C. PERCENT TRIPS BY INCOME S TRIP PURPOSE DISTRIBUTION . ENTER CURVE WITH INCOME AND DETERMINE % OF TRIPS BY PURPOSE. MULTIPLY BY TRIPS PRODUCED AS CALCULATED ABOVE TO OBTAIN TRIPS PRODUCED BY PURPOSE.

c

158 TR AN SP OR TAT ION PL AN NIN G

OUTPUT: TRIP PRODUCTIONS BY PURPOSE INCOME S DATA FOR CURVES FROM O-D SURVEY.

FIGURE 6-6 Example of urban trip production procedure. (Courtesy federal Highway Administration.)

b e c o m e t l i e p r e d o m i n a n t t e c h n i q u e C o r t r i p d i s t r i b u t i o n. Th e o r i gi n a l ve r s i o n o f t h e m o d e l , wh i c h wa s i n t r o d uc e d b y Vou c h e e s (16), wa s o f t h e fo r m : _A_

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Total trips = 1 1 0 T h e gr a vi t y m o d e l h a s b e e n mo d i fi e d i n r e c e n t ye a r s t o r e fl e c t r e s e a r c h a n d e xp e r i e n c e wi t h t h e mo d e l , i t h a s b e e n fo u n d t h a t d e c r e a s e s i n t r a ve l p r o p e n s i t y a r e m o r e c l o s e l y r e l a t e d t o t r a ve l t i me i l i a i t t o d i s t a n c e . In a d d i t i o n , i t l i a s b e e n e s t a b l i s h e d t h a t t h e e xp o n e n t o f t r a ve l t i me , ? t, va r i e s n o t o n l y wi t h t r i p p u r p o s e b u t a l s o wi t h t r i p l e n gt h . Tri p d i s t r i b u t i o n a n a l ys e s a re t h e r e fo r e u s u a l l y s t r a t i fi e d a c c o r d i n g t o t r a ve l t i me I wi t h d i ffe r e n t c a l i b r a t e d va l u e s o f t h e e xp o n e n t b e i n g d e t e r mi n e d fo r a gi ve n c i t y a n d t r i p l e n gt h . F u r t h e r mo r e , t o fa c i l i t a t e e ffi c i e n t c o mp u t e r u s e o f gr a vi t y m o d e l s , i t i s n o w t h e p r a c t ic e t o r e p r e s e n t t h e e ffe c t o f s p a t i a l s e p a r a t i o n o n t r a ve l b e t we e n z o ne s i n t h e fo r m o f t r a ve l t i me fa c t o r s F=

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wh e r e C i s a c o n s t a n t . In s t e a d o f a s u r r o ga t e me a s u r e o f a t t r a c t i ve n e s s s u c h a s c o m m e r c i a l fl o o r s p a c e u s e o r n u mb e r o f e mp l o ye e s , a c t u a l z o n a l t o t a l t r i p a t t r a c t i o n s a r e u s e d i n t h e e q ua t i o n . C u r r e n t, gr a vi t y mo d e l s p e r m i t a n a n a l ys t t o m a ke ad j u s t me n t t o al l o w fo r s pe c i a l s o c i a l o r e c o n o m i c c o n d i t i o n s b y c h o i c e o f s o c i o e c o n o mi c a d j u s t me n t fa c t o r. C u r r e n t l y, t h e r e c o m m e n d e d fo r mu l a t i o n o f t h e gr a vi t y mo d e l i s AjF, K j .

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wh e r e F t “ t r a ve l t i m e fa c t o r fo r t r a ve l t i me b e t we e n z o n e s i a n d / - K,j = s oc i o e c o n o m i c a d j u s t me n t fa c t o r b e t we e n z o n e s t a n d j Aj “ t o t a l a t t r a c t i o n s a t z o n e j The Fratar method P r o p o s e d b y T.j . F r a ta r i n 1 9 5 4 , t h i s me t h o d i s d e s i gn e d t o c o m p u t e t r i p i n t e r c h a n ge s wh e r e t h e r e i s n o n u n i fo r m gr o wt h wi t h i n va r i o u s s e c t i o n s o f a s t u d y a re a . Th i s me t h o d a n d va r i a t i o n s o n i t a r e c a l le d “ gr o wt h fa c t o r ” m e t h o d s . A gr o wt h fa c t o r fo r a pa r t i c u l a r z o n e i s s i mp l y' t h e r a t i o o f e xp e c t e d fu t u r e t r a ffi c t o t h e e xi s t i n g t ra ffi c e ma n a t i n g fr o m t h e z o n e . Ac c o r d i n g t o t h e F r a t a r me t h o d , fu t u r e t r a ve l p a t t e r n s b e t we e n

z o n e s a r e d e t e r m i n e d b y t h e p r e s e n t t r a ve l p a t t e r n s a n d gr o wt h fa c t o r s a t t h e d e s t i n a t i o n z o n e . Th e m e t h o d i s an i t e r a t i ve fa c t o r i n g p r o c e s s i n wh i c h t h e n u m b e r o f fu t u r e o r i gi n s a t e a c h z o n e i s h e l d c o n s t a n t, ft i s a na l o go u s to the Hardy Cross method of

s u c c e s s i ve a p p r o xi m a t i o n s fo r mo me n t e i i s l. r i b u t . i o n i n i n d e t e r mi n a t e s t r u c t u r e s . In r e c e n t ye a r s , t h e me t h o d h a s b e e n p r i nc i p a l l y u s e d t o p r e d i c t t r i p i n t e r c h a n ge s b e t we e n e xt e r n a l s e c t i o n s o f a s t u d y a r e a . It h a s al s o b e e n e m p l o ye d fo r s t a t e wi d e t r a n s p o r ta t i o n s t u d i e s. F o r fu r t h e r i n fo r m a t i o n o n t h e F r a t a r m e t h o d , t h e re a d e r s h o u l d c o n s u l t R e f. 1 7. Traffic assignment models Tra ffi c a s s i gn m e n t i s d e fi n e d a s t h e p r oc e s s o f d e t e r mi n i n g t h e r o u t e s o f t r a ve l a n d a l l o c a t i n g t h e z o n e - t o - zo n e t r i p s t o t h e s e r o u t e s . Th e p r o c e s s i s o n e o f t h e m o s t i mp o r t a n t a n d c o mp l e x p h a s e s o f t r a n s p o r t a t i o n p l a n n i n g. It i s a s ys t e m a t i c a n d r e p r o d u c i b l e t e c h n i q ue t h a t e n a b l e s t h e p l a n n e r t o p r e d i c t t h e p r o b a b l e t r a ffi c l o a d s o n e a c h s e gme n t o f a t r a n s p o r t a t i o n n e t wo r k. 'T h e c o s t s a n d o p e r a t i o n a l e ffi c i e n c y o f va r i o u s s ys t e m d e s i gn s c a n b e c o m p a r e d a n d e va l u a t e d a n d. a ft e r p r o p e r a n a l ys i s , t h e r e s u l t s m a y b e u t i l i z e d t o i d e n t i f y c h a n ge s t h a t wo u l d i mp r o ve t h e s ys t e m . Tra ffi c a s s i gn m e n t , i s a c o mp u t e r i z e d p r o c e s s, a n d t h e p l a n ne r mu s t fi r s t , d e s c r i b e t h e s t r e e t s ys t e m i n t e r ms t h a t wi l l fa c i l i t a t e c o mp u t e r p r o c e s s i n g. Th e s t r e e t o r h i gh wa y n e t wo r k i s de fi n e d b y “n o d e s ” a n d “ l i n ks . ” A n o d e i s a p o i n t : at : wh i c h t wo o r mo r e r o u t e s e c t i o n s me e t , a l l o wi n g fo r a c h a n ge i n t r a ve l d i r e c t i o n . A l i n k i s a o n e - wa y p a r t o f a r o u t e : t h a t l i e s b e t we e n t wo i n t e r s e c t i o n s o r n o de s . C o n t i n ge n c y c h e c ks a r e m a d e t o e n s u r e t h a t t h e c o d e d s ys t e m i s fr e e o f a n o ma l i e s a n d e r r o r s . T h e n fo r e a c h l i n k t h e fo l l o wi n g i n fo r m a t i o n i s u s u a l l y s t o re d i n t h e c o m p u t e r : ( 3 ) t h e l e n gt h o f t h e l i n k, ( 2 ) t he t r a ve l t i me o r s p e e d , a n d p o s s i b l y ( 3 ) t h e c a p a c i t y a n d e xi s t i n g vo l u me . T h e c o m p u t e r s e l e c t s t h e mi n i mu m- t i me p a t h s b y s ys t e m a t i c a l l y s e a r c h i n g t r a ve l l i m e i n fo r ma t i o n s t o r e d i n i t s me mo r y. Al l t h e mi n i m u m t i m e p a t h r o u t e s fr o m o n e l o a d i n g n o d e t o a l l o t h e r s c o n s t i t u t e a “t r e e , ” a n d t h e p r o c e s s i s c a l l e d “ t r e e b u i l d i n g. ” In t h i s p r o c e s s, t h e mi n i mu m t i m e p a t h a n d t r a ve l t i m e i s r e c o r d e d, Aft e r t h e t r i p s h a ve b e e n a s s i gn e d fr o m o n e z o n e , t h e c o m p u t e r t h e n s e l e c t s t h e n e xt zo n e a n d r e p e a t s t he process. In a s s i gn i n g t r a ffi c t o va r i o u s r o u t e s, i t i s s o me t i me s a s s u me d t h a t a l l d r i ve r s wo u l d c h o o s e t h e r o u t e wi t h t h e l e a s t t r a ve l t i me , a n d a s s i gn me n t s a r e m a d e o n a n “ a l l - o r-n o t h i n g” b a s i s. Th a t i s, a l l t h e t r i p s b e t we e n a gi ve n p a i r o f n o d e s wi l l b e a s s i gn e d t o t h e mi n i mu m - t i me p a t h a n d n o n e t o t h e n e xt s h o r t e s t t i m e p a t h. M o r e c o m mo n l y, t r i p s a r e p r o p o r t i o na t e l y a s s i gn e d t o t h e t wo b e s t r o u t e s o n t h e b a s i s o f t r a ve l t i me o r d i s t a nc e o r b o t h , E m p i r i c a l d i ve r s i o n c u r ve s h a ve b e e n d e ve l o p e d t o d e t e r mi n e wh a t p r o p o r t i o n o f a m o ve m e n t s h o u l d b e a s s i gn e d t o t h e s h o r t e s t p a t h. S o m e o f t h e t r a ffi c l o a d s o n t h e i n d i vi d u a l l i n ks ma y e xc e e d t h e c a p a c i t y o f t h e t r a n s p o r t a t i o n fa c i l i t i e s . Th i s wo u l d a ffe c t t h e t r a ve l t i me a n d p o s s i b l e c h a n ge t h e m i n i mu m- t i me pa t h s . 'Tra ve l t i me s a r e t h e r e fo r e a d j u s t e d a n d n e w m i n i m u m p a t h s a r e s e l e c t e d b y u s i n g t h e a d j u s t e d t i me s . W h e n t h i s i s d o n e a u t o m a t i c a l l y, i t i s c a l l e d “c a p a c i t y r e s t ra i n t " (18). Modal split models

M o d a l s p l i t m o d e l s a r e u s e d t o e s t i ma t e t h e p r o p o r t i o n o f fu t u r e ( p e r s o n ) t r i p s t h a t wi l l b e m a d e b y t r a n s i t a n d b y p r i va t e a u t o mo b i l e . S u c h models

164 TRANSPORTATION PLANNING

u s u a l l y c l a s s i f y t r i p s o r t r i p - e n d s b y t yp e a n d e c o n o mi c s ta t u s o f t he t r i p m a ke r a n d p r o vi d e a n e s t i ma t e o f p e r c e n t a ge o f t ra ve l b y t r a n s i t . Th e e s t i m a t e i s b a s e d o n s o m e c h a r a c t e r i s t ic o f t he t r a n s p o r t a t i o n s ys t e m s u c h a s r e l a t i ve t r a ve l t i m e s , d i s t a n c e s , o r co s t s . Th e mo d e l s t a ke t h e fo r m o f m a t h e m a t i c a l e q u a t i o n s o r e mp i r i c a l t a b l e s a n d c u r ve s . T h e r e a r e t wo ge n e r a l c la s s e s o f mo d a l s p l i t mo d e l s : ( 1 ) t r i p - e n d m o d e l s , i n wh i c h t h e origins and destinations a r e d i vi d e d b y mo d e , t i t a t. i s, b e fo r e t r i p d i s t r i b u t i o n ; a n d ( 2 ) t r i p - i n t e rc h a n ge mo d e l s , i n wh i c h t h e t r i p movements fo r e c a s t b y a t r i p d i s t r i b u t i o n a r e d i vi d e d b y mo d e . E m p i r i c a l e vi d e n c e i n d i c a t e s t h a t t he fo l l o wi n g fa c t o r s i n fl u e n c e m o d a l c h o i c e (19): 1 . Typ e o f t r i p ( e . g. , t r i p p u r p o s e, t i me o f d a y) . 2 . C h a r a c t e r i s t i c s o f t h e t r i p ma ke r ( e . g. , i n c o me , a ge , a u t o o wn e r s h i p , r e s i d e n t i a l d e n s i t y) . 3 . C h a r a c t e r i s t i c s o f t h e t r a n s p o r t a t i o n s ys t e m ( e. g. , r a t i o o f t r a n s i t t r a ve l t i m e t o a u t o t r a ve l t i me ) . In t e r e s t i n g l y, a n o p i n i o n s u r ve y (20) o f 9 0 p r o fe s s i o n a l p l a n n e r s a n d e n gi n e e r s re ve a l e d t h a t t h e mo s t i mp o r t a n t ma s s t r a n s p o r t a t i o n a t t r i b u t e s are 1. 2. 3. 4. 5. 6. 7.

R e l i a b i l i t y ( a r r i vi n g o n t i me ) . S a fe t y ( c r i m e , a c c i d e n t, e t c. ) . D o o r-t o - d o o r t r a ve l t i me . Tot a l t i m e s p e n t wa i t i n g. R i d e r ’s a t t i t u d e t . o wa r d p u b l i c t r a n s i t . P a r ki n g a va i l a b i l i t y a t s u b u r b a n t e r mi n a l s . Ter m i n a l a c c e s s a n d l o c a t i o n.

M a n y a t t r i b u t e s r e l a t e d t o c o mfo r t a n d c o n ve n i e n c e , s u c h a s a d j u s t a b l e s e a t s , a t t ra c t i ve n e s s o ft h e ve h i c l e , a n d p r o vi d i n g mu s i c , we r e r a n ke d r e l a t i ve l y l o w b y t h e r e s p o n d e n t s. M a n y p l a n n e r s b e l i e ve t h a t c u r r e n t mo d a l s p l i t a na l ys i s te c h n i q u e s a r e i n a d e q u a t e a n d u n r e l i a b l e , e s p e c i a l l y i n p r e d i c t i n g t r i p s b y “c h o i c e ” r i d e r s (20). F u r t h e r r e s e a rc h i s n e e d e d t o d e ve l o p mo d a l s p l i t mo d e l s t h a t wi l l t a ke i n t o c o n s i d e r a t i o n t h e e ffe c t s o f t e c h n o l o gi c a l i n n o va t i o n , p u b l i c p o l i c y, a n d s o c i o l o gi c a l c h a n ge s .

6-7 Plan generation and evaluation T h e n e xt s t e p i n t h e t r a n s p o r t a t i o n p l a n n i n g p r o ce s s i n vo l ve s t h e ge n e r a t i o n a n d e va l u a t i o n o f a l t e r n a t i ve t r a n s p o r t a t i o n p l a n s . A t r a n s p o r t a t i o n p l a n c o n s i s t s o f a s e t o f p r o p o s e d a c t i o n s t o i mp r o ve t h e t r a n s p o r t a t i o n s ys t e m a s we l l a s p o l i c i e s t o p r o t e c t a n d co n t r o l t h e c o n s t r u c t i o n a n d i m p r o ve m e n t o ft h e s ys t e m ( - ? ) ■ P l a n n e r s b e gi n wi t h t h e e xi s t i n g t r a n s p o r t a t i o n s ys t e m p l u s a n y '‘ c o m m i t t e d ” fa c i l i t i e s . C o m m i t t e d fa c i l i t i e s a r e t h o s e t h a t ha ve n o t . b e e n b u i l t b u t h a ve p r o gr e s s e d t h r o u gh t h e p l a n n i n g, d e s i gn , a n d p r o p e r t y a c q u i s i t i o n s t a ge s t o s u c h a n e xt e n t t h a t a p o l i c y d e c i s i o n h a s b e e n ma d e t o

S y s t e m s P l a n n i n g 165

b u i l d t h e m r e ga r d l e s s o f t h e o u tc o me o f t he c u r r e n t s t u d y ( 7 5 ). To t h e e xi s t i n g a n d c o m m i t t e d s ys t e m, fu t u r e t r a ffi c d e ma n d i s a p p l i e d b y t r a ffi c a s s i gn m e n t s . Th i s wi l l l i ke l y r e ve a l d e fi c i e n c i e s i n t h e e xi s t i n g a n d committed n e t wo r k ( e . g. , h i gh vo l u me / c a p a c i l y r a t i o s ) . A n e w t r a n s p o r t a t i o n p l a n i s fo r m u l a t e d a n d e va l u a t e d o n t h e ba s i s o f go a l s , o b j e c t i ve s , c o n s t ra i n t s , a n d e va l u a t i o n c r i te r i a . S e e F a b l e 6 - 3. S u c h a p r o c e s s i s c o n t i n u e d i t e r a t i ve l y, e mp l o yi n g p la n n i n g mo d e l s p r e vi o u s l y d e s c r i b e d . To t he e xt e n t p o s s i b l e , t h e c o n se q u e n c e s o f e a c h al t e r n a t i ve p l a n s h o u l d b e e s t a b l i s h e d, p r e fe r a b l y i n q u a n t i t a t i ve t e r ms ( h o u r s o f d e l a y, n u m b e r s o f p e r s o n s ki l l e d i n t r a ffi c : c r a s h e s , n u mb e r s o f fa mi l i e s d i s p l a c e d , p o u n d s o f e m i s s i o n s , e t c. ) . Th e i mp a c t s fr o m e a c h a l t e r n a t i ve p l a n s h o u l d b e e va l u a t e d i n t e r ms o f t h e go a l s t h a t we r e p r e vi o u s l y e s t a b l i s h e d . F r o m s u c h a n a l ys e s , s e ve r a l p r e fe r r e d al t e r n a t i ve p l a n s ma y e vo l ve , fr o m wh i c h t h e “ b e s t ” p l a n mu s t b e c h o s e n . It . ma y t h e n b e d e s i r a b l e t o r a n k t h e p r e fe r r e d p l a n s q u a n t i ta t i ve l y b y me a n s o f'a t t i t u d e s u r ve ys o r a r a t i n g p a n e l s i mi l a r t o t h e p r o c e d u r e d e s c r i b e d b y j e s s i ma n e l a i . (21).

6-8 Implementation of the plan Im p l e m e n t a t i o n i n vo l ve s t h o s e ac t i vi t i e s t h a t a r e ne c e s s a r y t o p u l t h e t r a n s p o r t a t i o n p l a n i n t o e ffe c t i n a n o r d e r l y ma n n e r. P l a n n e r s mu s t a c c o m p l i s h , t h i s s t e p c o o p e r a t i ve l y wi t h o t h e r s a s t h e p l a n n i n g p r o c e s s i s fo l l o we d b y o t h e r p h a s e s o f d e ve l o p me n t , ( l oc a t i o n , d e s i gn , p r o p e r t y a c q u i s i t i o n , e t c . ) . At t h i s p o i n t , l o c a l r a t h e r t h a n re gi o n a l go a l s a n d o b j e c t i ve s m u s t b e d e fi n e d a n d i n t e r p r e t e d i n l i gh t o ft h e p r o p o s e d t r a n s p o r t a t i o n i m p r o ve m e n t s . It i s vi t a l l y i m p o r t a n t t h a t t h e i mp r o ve m e n t s ca l l e d fo r i n t h e t r a n s p o r t a t i o n p l a n b e m a d e wi t h a mi n i m u m o f d i s r u p t i o n a n d a n n o ya n c e t o t h e p u b l i c . P ri o r i t i e s s h o u l d b e es t a b l i s h e d , a n d a c a p i t a l i mp r o ve m e n t p r o gr a m s h o u l d b e d e ve l o p e d i n wh i c h c o n s t r u c t i o n p r o j e c t s a re s t a ge d i n o r d e r o f t h o s e p r i o r i t i e s . Tra d i t i o n a l l y, p r i o r i t i e s h a ve b e e n “a s s i gn e d t o i m p r o ve m e n t p r o j e c t s l a rge l y o n t h e b a s i s o f s u b j e c t i ve j u d g me n t s d e ve l o p e d fr o m p a s t e xp e r i e n c e , P ri o r i t i e s t h a t a r e e s t a b l i s h e d s u b j e c t i ve l y r u n t h e r i s k o f p e r s o n a l e n gi n e e r i n g b i a s , l a c k o f c o mp r e h e n s i ve n e s s , a n d p o l i t i c a l b i a s . F u r t h e r m o r e , t h e i n c r e a s i n g n u mb e r, ma gn i t u d e , a n d c o m p l e xi t y o ft h e p r o gr a m s wi l l s o o n ma ke s u b j e c t i ve p r i o r i t y a n a l ys i s u n m a n a ge a b l e ” (22). F r e q u e n t l y, t h e ( p r o gr a m mi n g) p r o c e s s i s b a s e d o n a n e xa mi n a t i o n o f b a s e ye a r ( c u r r e n t ) c o n ge s t e d fa c i l i t i e s , an d t a rge t ye a r ( fu t u r e ) vo l u m e s o n fa c i l i t i e s . Im p r o ve me n t s t h a t ar e e xp e c t e d t o r e l i e ve c u r r e n t c o n ge s t i o n r e ce i ve h i gh e s t p r i o r i t y, t he n t h e o t h e r i m p r o ve m e n t s a r e gi ve n i mp o r t a n c e r e l a t e d t o t h e i r fu t u r e vo l u m e s . C o n s i d e r a t i o n s o f c o n t i n u i t y o f t h e s ys t e m wh i l e b e i n g c o n s t r u c t e d a n d t h e d i s t r i b u t i o n o f c a p i t a ! c o s t s o ve r t he ye a r s a r e e m p l o ye d t o c o n ve r t t h e p r i o r i t i e s i n t o fi ve - ye a r c o n s t r u c t i o n p r o gr a m s . ( 6 5 ) A n u m b e r o f s t a t e s h a ve pe r fo r me d h i gh wa y s u ffi c i e n c y a n a l ys e s a s a

m e a n s o f i d e n t i f yi n g wh e r e t h e h i gh wa y n e e d s a r e gr e a t e s t . S u c h s t u d i e s 166 'TRANSPORTATION PLANNING

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e m p l o y a r a t i n g s c h e m e t h a t a t t e mp t s t o c l a s s i f y t h e s e gme n t s o f a n e xi s t i n g h i gh wa y s ys t e m i n a ma n n e r t h a t i s u n p r e j u d i c e d, o b j e c t i ve , a n d u n i fo r m a s p o s s i b l e . Var i o u s e l e me n t s o f h i gh wa y s e c t i o n s a r e e va l u a t e d t o o b t a i n a m e a s u r e o f c o n d i t i o n o r s t r u c t u r a l ad e q u a c y, s a fe t y, a n d s e r vi c e . A c o m p o s i t e s c o r e i s c a l c u l a t e d fo r e ac h p r o j e c t a n d t h e p r o j e c t s a r e t h e n r a n ke d a c c o r d i n g t o t h e i r s c o r e s. O t h e r s t a t e s h a ve p e r fo r me d e c o n o mi c a n a l ys e s an d r a n ke d va r i o u s p r o j e c t s i n a c c o r d a n c e wi t h t h e i r e c o n o mi c i mp o r t a n c e . Typ i c a l l y, wh e n t h i s a p p r o a c h i s u s e d, be n e fi t - - c o s t r a t i o o r r a t e s o f r e t u r n , c o mp u t e d as d e s c r i b e d i n C h a p t e r 4 , s e r ve a s t h e ba s i s fo r p r i o r i t y a s s i gn me n t . M a k a n d J o n e s ( 2 2 ) p r o p o s e d t h e u s e o f a p r i o r i t y a n a l ys i s p r o c e d u r e t h a t i n c o r p o r a t e s a n u m b e r o f i n t a n gi b l e p a r a me t e r s s u c h a s c o n t i n u i t y c o n s i d e r a t i o n s , s t a t e a n d l o c a l p o l i t i c a l re a c t i o n s , a n d s o c i a l, ec o n o mi c , a n d e n vi r o n m e n t a l c o n s e q u e n c e s,

6-9 Maintaining the plan F i n a l l y, i t s h o u l d b e e m p h a s i z e d t h a t t r a n s p o r ta t i o n p l a n n i n g i s a c o n t i n u i n g a n d d yn a m i c p r o c e s s. P la n s s h o u l d b e c o n s t a n t l y r e a p p r a i s e d a n d m o d i fi e d t o r e fl e c t c h a n ge s i n l e ve l s o f fu n d i n g, l a n d u s e , s o c i a l an d e c o n o m i c c o n d i t i o n s, a n d c o mm u n i t y, s t a t e , a n d na t i o n a l go a l s . S u r ve i l l a n c e a n d u p d a t i n g o f i n ve n t o r y d a t a a n d p e r i o d i c r e a p p r a i s a l o l d l i e t r a n s p o r t a t i o n p l a n a r e r e q u i r e d i f i t i s t o b e r e s p o n s i ve 1 t o p u b l i c , wi s h e s a n d n e e d s.

6-10 Transportation planning software A gr e a t d e a l o f research e ffo r t h a s fo c u s e d o n t h e d e ve l o p me n t o f s t a n d a r d c o m p u t e r p r o gr a m s l o r t r a n s p o r t a t i o n p l a n n i n g. F o r e xa mp l e , t h e U r b a n Tra n s p o r t a t i o n P l a n n i n g S ys t e m { U 'F P S ) h a s b e e n ma d e a va i l a b l e b y t h e U r b a n M a s s Tra n s p o r t a t i o n Ad mi n i s t r a t i o n a n d t h e F e d e r a l H i gh wa y A d m i n i s t r a t i o n fo r t h e s u p p o r t o f s ys t e ms p l a n n i n g ( 2 5 ). D e s i gn e d fo r ma i n fr a m e computers, U TP S consists of c o mp u t e t ' p r o gr a ms , d o c u m e n t a t i o n , u s e r s ’ gu i d e s , a n d ma n u a l s. It i s s u i t a b l e lor u s e wh e r e t h e a l t e r n a t i ve s t o b e a n a l yz e d a re fe w i n n u mb e r, a n d t h e l e ve l o f d e t a i l i s s u ffi c i e n t t o p e r m i t e s t i m a t e s o f s ys t e m c o s t s, l e ve l s o f . s e r vi c e , major fa c i l i t y a n d c o r r i d o r vo l u m e s , a n d s o c i a l a n d e n vi r o n me n t a l i mp a c t s . B e gi n n i n g i n t h e 1 9 8 0 s, t r a n s p o r ta t i o n p l a n n e r s t u r n e d i n c r ea s i n gl y t o t h e u s e o f m i c r o c o m p u t e r s i n t r a n s p o r ta t i o n p l a n n i n g. E xt e n s i ve s o ft wa r e h a s b e e n d e ve l o p e d fo r m i c r o c o mp u t e r s a n d i s d e s c r i b e d i n p u b l i s h e d r e p o r t s o f t h e D e p a r t m e n t o f Tra n s p o r t a t i o n ( D O T) , fo r e xa mp l e , R e f. 2 4 . T h e F e d e r a l H i gh wa y Ad i u i n i s t t a t i o n fu n d s a mi c r o c o mp u t e r u s e r s u p p o r t gr o u p i n t r a n s p o r t a t i o n wh i c h p r o vi d e s s o ft t va r e a n d t e c h n i c a l a s s i s t a n c e a n d p u b l i s h e s a u se r gr o u p h u l l e t i n c a l l e d Microcomputers in Transportation (25). M i c r o c o m p u t e r s a re e s p e c i a l l y s u i t a b l e fo r s h o r t - t e r m p l a n n i n g a n d fo r t h e a n a l ys i s o f t r a ffi c i mp a c t s o f p r o p o s e d h i gh wa y s ys t e m c ha n ge s a l o n g c o r r i d o r s o r i n o t h e r s ma l l t o me d i u m - s i ze d p l a n n i n g s u b a r e a s . 'Th e s m a l l e r c o m p u t e r s h o l d t l i e p r o mi s e o f p r o vi d i n g a n a l yt i c a l c a p a b i l i t i e s i n t r a n s p o r t a t i o n p l a n n i n g t o m a n y mo r e a ge n c i e s a t l o w' c o s t a n d wi t h fa s t

response times. 170 'TRANSPORTATION PLANNING

162 TRANSPORTATION PLANNING

PROBLEMS 61 A household n avel survey is lo be made lor a cily with a population of ■■■12,000. Estimate (in today's dollars)t he cost of collect i tig data by home interviews, by telephone survey, and by mail survey. Assume an inflation rate of 0 percent per year and an average family size of 3.5. 62 Obtain a highway map and plan a travel survey for a nearby county or city using the roadside survey technique. Show the locations of survey stations on the map and prepare a report describing the planned survey times and durations and sample size. Indicate the size of survey crews and a description of duties for each crew member. Describe how the survey data could be used to estimate average daily traffic and design hourly volumes for the roads surveyed. 63 from current transportation literature, prepare a report briefly describing at least four trip distribution models. 64 Referring to the sketch shown in Section 6-6, calculate the interzonal trips due to 450 work trips produced at zone i. There are 750 attractions at zone 1, 400 attract ions at zone 2, and 500 attractions at zone 5. "The exponent, of travel time is 0.6, and the navel limes are: to zone 1, 9 min; to zone 2, 5 min; and to zone 3, 7 min. Assume all socioeconomic adjustment factors — 1,0. 65 Learn how die local transit agency measures the level of service provided to various areas of the city. Make a list of various measures that can lie used to describe t he amount of bus service provided to a given area or region.

REFERENCES 1. Creighton, Roger L. State of the An in Statewide Transportation Planning, Issues in Stalnvide Transportation Planning. Transportation Research board .Special Report No. Id6 (1974). 2. Pyers, Clyde E. Workshop !: Organization and Administration lor Statewide 1 ransporiation Planning. Transportation Research Board Special Report No. Mb (1971). 3. Statewide Transportation Planning Needs and Requirement.';. National Cooperative 1 lighwav Research Program Synthesis ol' Highway Practice 15, Highway Research Board. Washing ton, D.C. (1972). 4. Sturm, Byron. 1). Resource Paper. Transportation Research Board Special Report No, Mb (1974). 5. /ntergoverumenhd Review of federal Programs. Executive Order 12572, federal Register, Vol. 48, No, 16, January 24, 1983. 6. Campbell, E. Wilson. Workshop 11: Policy Planning. Transportation Research Board Special Report No. 14b (1974). 7. ’Transportation and Traffic. Engineering Handbook. Institute ol Transportation Engineers, Washington, D.C, (197b). 8. Mannat of Traffic Engineering Studies, 4th ed. Institute of Transportation Engineers, Washington, D.C, (197b). 9. (Rude for 'Traffic Volume daunting Matiual. Bureau of Public Roads, Washington, D.C. (1965). 10. Ha/.en, P. 1. A Comparative Analysis ok Statewide Transportation Studies. Highway Research Record No. -101 (1972). 11. DiRt m/o, John F. Travel Survey Procedures for Statewide Transportation Planning. Federal Highway Administration, Washington, D.C. (197b). 12. Urban Transportation Systems Associates. Inc. Urban Mass 'Transportation Travel Sur- cm. U.S. Department of'Transportation, Washington. D.C. (1972). 13. (loads 'Transportation in Urban Arens. Informational Report, institute of’ Traffic Kngineers, Washington, D.C. 14. Urban Origin Destination .STrcm. Federal Highway Administration, U. S. Department of Transportation, Washington, D.C.

References 172 15. A Policy on Design nj Urban !hylneays and Arterial Streets. American Association of State Highway and Transput tation Off icials. Washington, D.C. (1973). 16. Voorhees, A. M, A Ceneral ’fhcorv of d’raf f ic Movement. Proceedings of the Inslitule of 7 'rafjic E ngineers. A i 1 1 i gto , V a. {195")). 17. Kratar, T. ). Vehicular Trip Disti'ihiiiion b\ Successive Approximations. Traffic Quarterly. Vol. V I M . \T. 1. pp. 53--(if) (1959). 18. ’Traffic Assignment Manual. Bureau of Public: Roads, Washington, D.C. (1969). 19. Kertal, Marlin )., Weiner, K.d ward, Balek, Arthur j., and fjevin. All K. Modal Split. federal Highway Administration, Washington, D.C. (1970). 20. Wallin, Rex j,, ,md Wright, Raul H. 1‘actors Which influence Modal Choice. Traffic Quarterly, (April 19/9). 21. jessiman, William, et ;tl, A Rational Decision-Making Technique for Transportation Rkumiitg. 11/j‘hieny Research Record No. ISO (J967). 22. M;tk, K, fC, and [ones, Paul. Priority Analysis Procedure for Ranking Highway Im provement Projects. Tiauspurtatinn Research Record 56*5 (1976). 23. (A han Tiausjioilation Tin nning System: Introduction. Urban Muss Transportation Admin istration and federal Highway Administration, Washington, D.C. (December 1982). 24. Suftu'ii>e and Sourer Ruolt; Microcomputers in ‘Transportation. Urban Mass Transportation Administration. U.S. Department of Transportation, Washington, D.C. (February 1986). 25. Mia in, mi pu fn.\ in 'Tumsportation. User Group Bulletin, published periodically b y the Kedeial Highway Administration, Washington, D.C.

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