urban planning guide || intercity highway planning

CHAPTER 7

INTERCITY HIGHWAY PLANNING3

7.1 INTRODUCTION

Intercity highway planning may be defined as the development ofa highway system capable of moving people and goods between citiessafely, efficiently, and economically. Since highways are but one ofseveral modes available for the movement of people and goods, itfollows that intercity highway planning should be one element of theintercity transportation planning process. Intercity transportation in-cludes the highway, air, rail, waterway and pipeline modes.

A recent report by the National Cooperative Highway ResearchProgram (NCHRP) indicates that multimodal, intercity transportationplanning is not, however, the general method of approach. The reportindicates that most states develop plans one mode at a time, andcombine the single-mode plans in a statewide transportation plan.Irrespective of the procedures used to develop the statewide transpor-tation plan, the interrelationship and impact of one mode on othermodes is of significant importance. A well-defined, systematic approachis required to identify and properly consider these intermodal relation-ships and impacts.

The first step in developing a systematic approach should be toidentify significant issues, and to articulate the goals and objectives ofthe planning effort. Analytical work should then be structured to focuson these issues and to develop the information required to make in-formed decisions. All work should be coordinated with involved agen-cies at the state, regional and local levels, including public utility orservice commissions and private operators.

Issues confronting intercity highway planners are both broad inscope and complex. For example, intercity bus transportation posesdifficult problems: revenues that are just keeping pace with risingoperating costs, inadequate service to smaller communities, and threat-ened termination of service on low-patronage lines. There is also theissue of energy availability and cost which will influence the nation'sintercity passenger system. Increases in modal operating efficiencies willhave an impact on the market share captured by the individual modes.In addition, the United States freight system has been dominated byeconomic regulations for more than 50 years. The process is complicatedand has resulted in trucks and waterways eroding rail's market base.Further erosion of the rail system will place a greater stress on the

Prepared by Martin J. Fertal, M.ASCE, COMSIS Corporation, Pittsburgh, PA.

154

Urban Planning Guide

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INTERCITY HIGHWAY PLANNING 155

intercity highway network—a network that in some areas is alreadyseverely strained.

The foregoing paragraphs provide some insight into the complexityof planning transportation facilities at the intercity level. The process isdemanding in terms both of professional expertise and informationalrequirements.

Civil engineers not formally trained in transportation planningoften assume a major role as members of intercity highway planningproject teams. The effectiveness of the civil engineer in this role can beincreased with a basic understanding of the methods and proceduresemployed by the transportation planner.

The following sections of this chapter review some of the morecommon datasets and methods required to perform comprehensive,intercity highway analyses, and to evaluate the results obtained throughthis process. The steps to be followed in using this output to develop thetransportation plan are then outlined.

7.2 INTERCITY DATA REQUIREMENTS

The planning of intercity highway facilities can be accomplished ina manner similar to that employed in the urban transportation planningprocess, by means of data collection, data analysis and model develop-ment, travel forecasting, and systems analysis and evaluation. Thisplanning process requires a variety of information to simulate base yearconditions and develop forecasts of future travel demand and facilityneeds. The types of data required can be grouped into three generalcategories: (1) Socioeconomic; (2) facility; and (3) travel. The samegeneral categories have often been referred to as characteristics of thetrip, the trip-maker, and the transportation system. The terminologyused is unimportant. Information describing all components of travel is,however, of utmost importance.

7.2.1 Socioeconomic Data

Socioeconomic data refer to the characteristics of study areas andpeople that affect the demand for travel facilities. Examples of these datainclude population, employment, vehicle ownership, average familyincome, land use patterns, and employment by type. The importance ofthis information is that it describes an area and its inhabitants andprovides the facts required to develop relationships with existing trip-making characteristics for use in forecasting models.

The most readily available source of social and economic statisticsis provided by the U.S. Bureau of the Census. Many state and regionalplanning agencies have additional data available as a result of localsurveys and sources. Also, a great deal of data is typically availabledirectly from private carriers and other organizations.


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156 URBAN PLANNING GUIDE

7.2.2 Facility Data

Facility data provide information on the existing condition andperformance of the system. This information is required to developtraffic assignment computer models, measure system performance,structure traffic engineering improvements, and undertake the manyadditional analyses requiring facility input.

Highway facilities Highway facility information required by link (seeFig. 7-1) or section, or both, includes pavement type, administrative andfunctional classification, capacity, volume, average operating speed,vehicle miles of travel by type, and number and percentage of trucks bytype. Other data, including surface condition and geometries, are desir-able for safety planning purposes. Information relative to total cost andtotal revenue is necessary to perform the economic analysis portion ofany comprehensive planning effort. The prime source of this informa-tion is a state department of transportation (DOT). If the DOT does nothave it and does not know where to obtain it, it is highly probable thatthe facts are unknown and must be collected.

Other facility data Intercity highway facilities serve autos, buses, andtrucks engaged in the movement of persons and goods. The intercitytransportation system also includes the air, rail, water and pipelinemodes. It is a complex system requiring a broad planning perspective.

Required intercity bus and truck information includes: passengerand freight schedules; equipment available (type, age, capacity, etc.);annual revenues and cost; number of persons carried; tons of freightmoved; size, location, and other attributes of terminal facilities. In mostinstances, this data-collection work will require direct contact with theprivate carriers (e.g., Greyhound Bus Company) and most probably thestate public utility or public service organization.

7.2.3 Travel Data

Travel data are required to establish existing travel patterns. Infor-mation on the origin and destination of existing passenger trips and

Fig. 7-1. Node, Link, Section Example


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freight movements must be obtained before any understanding of ex-isting travel can begin to develop. In addition, other attributes of thesetrips, such as purpose, income level of trip-maker, mode utilized, timeof day and day of v/eek trip was made, and cost of trip should beobtained. With information of this type, models to simulate existingconditions and to forecast future conditions can be developed andcalibrated.

The collection of existing travel data is difficult, time consumingand expensive. For these reasons, every effort should be made to locateand utilize existing sources. These existing sources should be carefullyreviewed to assure their usefulness. The alternative is the collection ofnew travel data for intercity highway planning purposes. This could beaccomplished, depending on the goals and objectives of the planningstudy, with cordon counts, roadside interviews, home interviews, mail,telephone, on-board transit, special truck, or combinations of the surveymethods. Irrespective of the method used, the objective of the data-collection phase is to assemble socioeconomic, facility, and travel data tothe level of comprehensiveness required to address and satisfy theestablished goals and objectives.

Upon completion of the data-collection work, the next phase is theanalysis of available data and the development of computerized plan-ning models for use in the travel forecasting phase.

7.3 DATA ANALYSIS AND MODEL DEVELOPMENT

The data-collection phase of any planning effort can produce agreat deal of interrelated yet uncoordinated information. Summary andanalysis of this information is required to establish the validity andreasonableness of the base dataset, and to assist in its orderly, efficientuse.

It used to be that simply to summarize various sources of informa-tion was not an easy task. Computer resources were not always availableto analysts. Where computer resources were available, expertise andsoftware, or both, were often unavailable. As a result, a substantialamount of data reduction and analysis work was done manually. Theintroduction of the low-cost microcomputer and user-oriented softwareis dramatically changing data reduction and analysis efforts. In the past,many pages in many manuals were filled with instructions on how touse a certain program to obtain simple tabulations. Most agencies nowhave the capability to summarize data quickly and easily.

The summary and analysis of base data are prerequisites to thedevelopment of transportation planning models. The following subsec-tions will examine the three basic models in the transportation planningprocess: (1) Trip generation; (2) distribution; and (3) assignment. Thesemodels can be employed, irrespective of area, in any highway or trans-portation planning effort. They can be employed at any scale, e.g., on amain-frame computer, a mini, a micro, or even manually, as explained


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in Reference 7. A general understanding of the models is important toany civil engineer involved or associated with a planning function.

7.3.1 Trip Generation Modeling

Trip generation is a term used by the transportation planner todescribe the relationship between trip characteristics and land-use orsocioeconomic characteristics. For example, it is intuitively known thatthe number of work trips originating in a residential area is related to thelabor force residing in that area. Furthermore, it can be generalized thatthe number of work trips attracted to an area is somehow related to theemployment in the area. The quantification of these and other similarrelationships produces a set of equations which collectively are termedthe trip generation model.

The trip generation model is an integral element in the transpor-tation planning process. However, the model answers only one ques-tion: How many trips start or end in a given analysis unit? In theplanning process, these analysis units are normally referred to as trafficanalysis zones. Other questions about the trip such as mode, direction,length, duration, and routing are answered by other planning models.The trip generation model thus quantifies the relationship between thenumber of trips beginning or ending in any analysis unit with that unit'sland use and socioeconomic characteristics. From this basic understand-ing of the interaction between travel and the surrounding environment,forecasts of future travel can be made that are both meaningful andresponsive to changes continually occurring in study areas.

The primary purpose of this subsection is to provide an overviewof the generation model. For this reason, the material does not includeinformation relative to background or theory, which can be found innumerous publications, including two published by the Federal High-way Administration (4, 11).

Analysis techniques Three basic analysis techniques have been usedto develop trip generation relationships: (1) Simple rate; (2) regression;and (3) cross-classification. To illustrate, assume that a data-collectioneffort was undertaken and produced information by analysis unit of atype shown in Table 7-1.

Analysis of the data in Table 7-1 would show, for example, that theaverage number of trips per person in the study area is equal to 2.10(1010/480). More detailed investigation would show a meaningful rela-tionship between median family income and trip-making expressed interms of trips per person. A plot of the actual data points and aleast-squares fit of these data with a linear regression line of the form Y= A + BX would be as shown in Fig. 7-2.

Another way of analyzing these data might be to compute theaverage number of trips per person by automobile ownership group;e.g., 1.00 or less autos per dwelling unit, greater than 1.00 but less than2.00 autos per dwelling unit, and greater than 2.00 autos per dwelling


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TABLE 7-1 Transportation Planning Data (Hypothetical Five-ZoneStudy Area)

Zonal Characteristics

Total populationNumber of dwelling unitsMedian family income,

in dollarsAutos per dwelling unitTotal number of tripsHome-based work trips*Home-based other tripsNon home-based tripsTrips by autoTrips by transit

Traffic Zone

1

10033

10,000

1.0200666767

16040

2

15043

7000

0.82251005075

16956

3

9030

1 1 ,000

1.120060

10040

17030

4

7029

13,000

1.217546

10029

15718

5

7028

18,000

2.021050

11050

20010

Total

480163N/A

N/A1010322427261856154

*A home-based trip is defined as a trip having one end at home. A nonhome-based trip is defined as one having neither end at home.

Fig. 7-2. Trips per person versus median family income


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TABLE 7-2 Trips per Person as Related to Autos perDwelling Unit

Trips per person

Autos per dwelling unit

1 .00 and less

1.70

1.01-2.00

2.34

2.00 +

3.00

unit. This analysis would result in the type of information shown inTable 7-2.

The preceding has demonstrated three methods of developingrelationships between a dependent travel variable (number of trips, tripsper person) and independent socioeconomic variables (persons, medianfamily income, autos per dwelling unit). The first method falls into thecategory of a simple rate or average. The second demonstrates a datafitting or regression technique. The third fits the category of cross-classification. All three techniques are used in the planning process todefine the relationship between travel and socioeconomic factors. Therelationships thus defined have come to be known as the trip generationmodel.

7.3.2 Trip Distribution Modeling

The trip distribution model is a major element in the integratedtransportation planning process. The purpose of the model is to convertzonal trip ends into travel movements or, in other words, to tell wherethe trips are going. To accomplish this objective, two trip distributionmodels—the Fratar model and the gravity model—have been used mostextensively. Examples of the method of computation for both modelsfollow.

Fratar model The Fratar model can be classified as an iterative, growth-factor type trip distribution model. The model is structured on thepremise that:

1. The future volume of trips out of a zone is related to the presentvolume of trips out of the zone and the growth estimated for the zone.

2. The future distribution of trips from a zone is proportional tothe present distribution of trips from the zone modified by the growthexpected in the zones to which the trips are attracted.

To illustrate the working of the model, consider the three-zoneexample shown in Fig. 7-3. There are now 10 trips between zones Aand B (tab = 10), 20 trips between zones A and C (tac = 2Q), and 15 tripsbetween zones B and C (tbc = l5). Also, the trip production of zone Ais expected to double (Fa = 2), the trip production of zone B is expected


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Fig. 7-3. Three-zone example

to triple (Fb = 3), and the trip production of zone C is expected to re-main constant (Fc = l). An estimate of the future distribution of tripsbetween zone A and zones B and C is obtained in a seven-step, itera-tive manner. The calculation underlying the Fratar process can befound in Section 7.7 of this chapter.

The computations are made for each zone in the study area.Modified growth factors are computed and used in a second iteration ofthe model. The iterative process continues until all factors converge towithin acceptable limits of 1.00. Two points should be recognized rela-tive to the Fratar model: (1) The model can only work if given an existingtrip matrix to expand, and (2) it does not consider the characteristics ofthe transportation system.

Gravity model The second trip distribution model to be considered isthe gravity model. In essence, the gravity model says that the distribu-tion of a given zone's trip production of P/ is directly proportional to theattraction power of other zones Aj and inversely proportional to somefunction of the spatial separation between the two zones, rfi_x. In equa-tion form

in which Tz.; = trips from zone / to zone ;; Pz = trips produced at zonerf AJ = trips attracted at zone /; rfz_; = measure of impedance (spatialseparation) between zones / and ;'; Z = empirically derived exponent; N= number of zones; and, Ax = trips attracted at zone x.

The denominator of the gravity model is usually referred to as theaccessibility index. It represents the total accessibility of any zone / to allzones in the study area. More relating to accessibility is included in latersections of this chapter.

(7.1)


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A slight rearrangement of the gravity model formulation makes iteasy to see that the model merely distributes trip productions of zone ito other zones on the basis of another zone's attractiveness relative tototal system attractiveness.

In reference to the examples, it should once again be noted that theFratar model is not responsive to changes in the transportation system.It has no way of accounting for a change in travel patterns that wouldoccur as a result of transportation system changes such as a new bridgeor a circumferential highway. On the other hand, the gravity model isresponsive to changes in the transportation system. These changes arereflected by the model through the use of zone-to-zone travel imped-ances (e.g., travel time).

Each model has its role in the planning process. The Fratar can beused to develop estimates of revised zone-to-zone trip interchangesresulting from changes that are not changes in the highway system. Anexample would be expected, unequal growth in various cities in thestate. The gravity model can be used to develop similar estimatesreflecting, for example, improved accessibility between a given city pair.

7.3.3 Traffic Assignment Modeling

Traffic assignment is a process used to develop loadings on anetwork of transportation facilities. The result of the assignment processis an estimate of user volumes on each segment (link) of the network aswell as the turning movements at intersections of the links. Trafficassignment is used to simulate existing traffic volumes on a transporta-tion system and to forecast probable future volumes. This simulationrequires the use of trip interchanges (trip table) obtained in the origin-destination (O-D) survey or developed as a result of the distributionprocess. The volumes used may be number of vehicles, number of totalpersons, number of transit riders or any other user characteristic that canbe described by an origin, a destination, and some quantifiable tripinterchange characteristic. Traffic assignment is used for many reasons,including:

1. The development and testing of alternative transportation sys-tems.

2. The establishment of short-range priority programs for trans-portation facility development.

3. The detailed study of traffic generators and their effects on thetransportation system.

4. The development of a specific location for facilities and servicewithin a transportation corridor.

5. The development of design hour volumes.6. The development of necessary input and feedback to other

planning tools.

Required inputs Input to the traffic assignment process, regardless of


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the type of network to be considered (transit, highway, rail, etc.),includes:

1. Network geometry. A description of the links and their inter-connections, this may be viewed as a map containing the network to bestudied.

2. Network parameters. The assignment process requires net-work link values in order to determine routes through the networkunder study. Only one value is required and may be, for example, traveltime, distance, cost, or a combination thereof. No other network param-eter is required, but other parameters are highly recommended forspecial analytical purposes.

3. Interchange values. The unit to be loaded onto the transpor-tation network by the assignment process is described by an origin, adestination, and an interchange value. The value may be, for example,vehicles, persons, tons of cargo, etc.

Assignment outputs The output of the traffic assignment process con-sists basically of loads on each link of the transportation network. Thesemay be 24-hr vehicular highway traffic volumes, peak hour transitvolumes, or yearly volumes of freight flow. In addition to the linkvolumes, the assignment process produces turning movements at linkintersections, minimum routings through the transportation network,and the minimum summation of impedances between origins and des-tinations.

Assignment techniques rely on the determination of routesthrough a network of facilities based upon link impedances such as time,distance, or cost of travel. Interchange values described by an origin anddestination are then accumulated on the network links comprising thepath or paths calculated between the origin and destination. The accu-mulation of all O-D interchange values on the network links is the loadon the transportation network.

The traffic assignment process is but one procedure in the trans-portation planning process. The results are, however, widely usedbecause they are readily understood by administrators, the public, andgeneral planners. In addition, intermediate results (e.g., zone-to-zoneimpedances) are used for other analytical procedures such as modalsplit, trip generation, and land use distribution. Since the final link loadsprobably receive more exposure, analysis, and evaluation than any oneother output of the process, it is recommended that considerable care beused to assure their reasonableness.

Uses of traffic assignment The assignment technique is first utilized inthe planning process to assess the adequacy of the trip data obtained inthe O-D survey. The coded and factored survey trips are assigned to thenetwork for survey validation purposes. The assignment techniqueprovides an inexpensive and efficient means of accumulating O-D tripsacross screenlines as well as through corridors for comparison with


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ground counts. In addition, the selection of traffic analysis zones andnetwork coding should be evaluated by traffic assignment to assurereasonable link volumes.

Traffic assignment is also used to obtain zone-to-zone impedancesfor input to other planning tools. These impedance values are initiallybased upon travel time surveys; however, network calibration andcapacity restraint will modify these initial values. The effect of thesemodifications should be well understood by the analyst, since thezone-to-zone impedances will be used as a basic input to subsequent tripdistribution and modal split modeling. Also, these impedance measuresare used by several land use distribution models currently in use.

The trip distribution and modal split model calibration process alsorelies on traffic assignment; i.e., model trips are loaded on the basenetwork and compared to O-D travel. Comparisons are normally madeby screenline, portions of screenlines, functional classification, andindividual links. The basic types of traffic assignments made in a com-prehensive study include:

• Existing trips to the existing network.• Future trips to the existing plus committed network.• Future trips to the existing plus committed plus proposed net-

works.

These types of assignments are made to aid in formulating and evalu-ating alternative transportation systems for serving future demand.Additionally, traffic assignment is used for:

• Priority planning through the assignment of travel for interme-diate years to their corresponding systems.

• Detailing of route locations through established corridors andstudying in more detail features such as alternative interchangelocation.

• Evaluating the effects of new and large generators such asairports, housing developments, and commercial complexes onthe surrounding transportation system.

• Development of design hour volumes and other factors neces-sary for the detailed design of facilities.

7.4 TRAVEL FORECASTING

Projections of population and economic activity have long been thebasic inputs underlying forecast of travel demand. Since there is a greatdeal of uncertainty in any forecast of population or economic activity, itfollows that there is a great deal of uncertainty in any forecast of traveldemand. The degree of uncertainty has become even greater with majoradjustments in the economic and energy sectors. These adjustments anduncertainties dictate that single point forecasts are probably inadequate


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for all but the least important and least comprehensive planning efforts.Efforts of significance should attempt to measure the impacts of variousscenarios designed to bound the probable range of outcomes.

Once basic input variables are available, the travel models thatutilize these variables can be solved to produce travel demand estimates.These input variables include future estimates of all independent vari-ables used in the base-year travel models. Examples of typical indepen-dent variables include population, employment, highway speed, high-way capacity, and transit operating cost.

It should be noted that forecast data are not always readily avail-able; furthermore, that forecast data are subject to error. Judgment isrequired in the development of the base-year models to assure thatnecessary future-year inputs are both obtainable and reliable.

The specifics of the travel forecasting process will vary from state tostate, and possibly from project to project. A generalized approach ispresented by Fig. 7-4, which illustrates the major work elements in thetravel forecasting process and the interrelationship between the ele-ments.

7.5 SYSTEMS ANALYSIS

At the conclusion of the travel forecasting phase, a large amount ofinformation will be available. This information will include projectedtraffic volumes, minimum time and distance paths, travel patterns,

Fig. 7-4. Statewide forecasting steps (10)

INDEPENDENTSTATE

TRAVEL ESTIMATES

CHECK

EVALUATION

PLANDEVELOPMENT

FUTURETRAVEL

PATTERNS

BASE YEARZONES ANDNETWORK

•CHECK

BASE YEARTRAVELPATTERNS

DATA

FORECAST STATESOCIO-ECONOMICCONTROL TOTALS

ALLOCATIONPROCEDURES

FUTUREFUNCTIONAL

SYSTEMALTERNATIVES


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vehicle-miles of travel, insight into the economic and social impacts ofvarious alternatives, and other associated data.

The next phase of the transportation planning process is systemsanalysis. It can be concisely summarized as a three-step process: (1)What is the problem? (2) What are the alternatives? (3) What is the bestalternative? For example, if the problem is to reduce transportationenergy consumption, the alternative that minimizes vehicle-miles oftravel is a logical, best alternative.

In practice, the selection of the best alternative is rarely as straight-forward as the example. There are typically many system performancemeasures of varying importance to be considered. Many analysts handlethis problem by completing a table similar to Fig. 7-5. The weightattached to each measure is normally obtained by soliciting input frominvolved participants.

To illustrate the systems analysis process, assume the problem is toevaluate the quality of existing intercity bus service and the effect ofproposed intercity bus improvements. The structuring of the systemsanalysis effort could be accomplished in many different ways. The extentof the analysis effort is largely dependent on the availability of resources.In any event, performance measures to be used in evaluating alternativeimprovement plans must be developed. As in almost all analyses, thecost of the proposed improvements is an important performance meas-ure. In addition, the problem indicates that the quality of existingintercity bus service and the effect of proposed improvements is to bequantified.

In this example, the use of a relative service index—the ratio ofintercity bus travel time (including access, egress, and transfer time) tointercity auto time—is an appropriate performance measure. This indexprovides a method of quantifying the relative level of existing intercitybus service and testing the effect of proposed improvements.

The development of the relative service indices for all city-to-citypairs can be rather easily accomplished using the Urban Mass Transpor-tation Administration's Urban Transportation Planning System (UTPS).

Fig. 7-5. Table of alternatives


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The work involved to establish base year conditions includes the codingof the intercity networks and a series of computer runs. The workinvolved to reflect proposed service improvements involves revisions tothe coded networks and additional computer runs.

The information presented in this section briefly illustrates thesystems analysis phase of the urban transportation planning process.The scope of this phase is dependent on the complexity of the problemand available resources. The structure of this phase should, however, berelatively constant. Articulation of the problem, identification of theavailable alternatives, and selection of the best available alternative onthe basis of well defined performance measures are the keys to profes-sional systems analysis.

7.6 CONCLUSION

Intercity highway planning is a complex area requiring a broadperspective, a reasonable level of staff expertise, and adequate re-sources. The perspective required is a function of the goals and objec-tives of the planning effort. It is important that the goals and objectivesbe well defined at the beginning of the project and that technical workbe structured to focus on these areas.

Adequate methodology and computerized procedures are availableto address most intercity highway planning projects. These methodsand procedures form a planning process. The major steps in the plan-ning process are the articulation of goals and objectives, data collection,data analysis and model development, travel forecasting, and systemsanalysis and evaluation. Each step has been described in a previoussection of this chapter.

The use of these methods and procedures provides a structuredapproach to analyze the capability of existing highway systems to meetcurrent and future needs. They also provide a capability to analyzefuture alternative systems and their ability to meet future needs. Itshould be recognized, however, that the networks used to representsystems in the planning process must be translated into plans and theninto projects. This involves additional work not described in this chap-ter. This additional work can include engineering feasibility analyses,cost estimation, environmental appraisal, and other similar analyses.

The structured planning process described in this chapter is a goodfoundation on which to build an intercity planning effort. It does,however, have its limitations. It is highly demanding of data, computerresources, expertise and time. A decision is therefore required early inthe process relative to the methods and procedures to be employed. Thedecision as to the appropriate analytical approach will be largely influ-enced by time and budget constraints. Proper systems analysis at thispoint in the process may dictate that the best approach is an approachother than that described, that is, the manual NCHRP 187 methodology(7).


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It is not possible to provide a recommended approach for a subjectas complex as intercity highway planning that will be valid for eachindividual effort. It is, however, possible to provide a general structurefor developing a recommended approach for each intercity planningeffort. Briefly, the steps are:

1. Articulate the goals and objectives of the planning effort.2. Define study constraints, e.g., time, cost, available resources,

etc.3. Employ basic systems analysis procedures to select the most

appropriate method of approach; What is the problem? What are thealternatives? What is the best alternative?

4. Use the selected approach to produce probable impacts ofalternative systems.

5. Evaluate the various alternatives again, using the basic systemsanalysis approach in conjunction with previously agreed upon perform-ance measures to select the best available alternative.

6. Translate the best alternative into an implementation planincluding individual project statements.

The use of a systematic approach similar to the one described above willprovide structure to the planning process and produce results consistentwith the stated goals, objectives and available resources.

7.7 APPENDIX A—FRATAR DISTRIBUTION MODEL

Use of the Fratar model follows a seven-step iterative calculationprocedure. The first step is to estimate trips between zone A and zoneB considering the growth of zone A, by means of

Tab (a) =

Tab (a) =

Tab (a) = 36.0

Next, estimate trips between zone A and zone B considering growth ofzone B, using

Tab (b) =

Tab (b) = 42.8


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Arrive at the best estimate of trips between zone A and zone B bymeans of

Tab

Tab

Tab = 39.4

Estimate trips bewteen zone A and zone C considering growth of zoneA, using

Tac (a) =

Tac (c) = 24.0

Estimate trips between zone A and zone C considering growth of zoneC, using

Tac (c) =

Tac (c) = 14.7

Arrive at the best estimate of trips between zone A and zone C by meansof

Tac

Tac

Tac = 19.3

Compute modified growth factor to be used in next iteration of model bymeans of

Fa

Fa

Fa = 1.18


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7.8 REFERENCES

In the preparation of this chapter, reference was made to Chaps. 1,2, 3, and 6 of this Urban Planning Guide. Other useful references are:1. COMSIS Corporation, Estimating Long Range Highway Improvements and Costs,

prepared for the U.S. Department of Transportation, Washington, DC,August 1977.

2. COMSIS Corporation, Nebraska Public Transit Study, Nebraska Office ofPlanning and Programming, Lincoln, NE, 1973.

3. "Evaluating Options in Statewide Transportation Planning/Programming/'Report No. 179, Transportation Research Board, Washington, DC, 1977.

4. Guidelines for Trip Generation, Federal Highway Administration, Washington,DC.

5. Klink, W.D., and Yu, J.C., "Propensity of Statewide Multimodal Transpor-tation/' journal of the Transportation Engineering Division, ASCE, Vol. 101, No.TE4, November 1975, pp. 639-655.

6. Levinson, H.S., "Highways, Transport, and Energy: A Look Ahead/' Jour-nal of the Transportation Engineering Division, ASCE, Vol. 108, No. TE5,September 1982, pp. 447-456.

7. "Quick Response Urban Travel Estimation Techniques and TransferableParameters," Report 187, National Cooperative Highway Research Program.

8. "State Transportation Issues and Actions," Special Report 189, TransportationResearch Board, Washington, DC, 1980.

9. "Statewide Transportation Planning," Report No. 95, Transportation Re-search Board, Washington, DC, November 1982.

10. "Statewide Travel Demand Forecasting," Transmittal 147, Vol. 20, App. 59,U.S. Department of Transportation, Washington, DC, November 1973.

11. Trip Generation Analysis, Federal Highway Administration, Washington, DC.


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