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TRAFFIC ACCESS/IMPACT STUDIES.
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Use by local govts. in development projects, purpose, need for, procedures, computers.... More...
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Paper Abstract:
Use by local govts. in development projects, purpose, need for, procedures, computers.
Paper Introduction:
Traffic Access/Impact Studies
In many United States cities, traffic congestion has become a major public policy issue. Furthermore, most large-scale development significantly alters a community's transportation environment. However, despite increasing demand for urban development, local governments are often limited in their ability to fund infrastructure improvements such as roadway construction. During the 1980s, such factors led to widespread concern regarding the traffic impacts of various urban site developments. One method of determining whether or not a given area's roadway network can support a development's traffic is to perform a site traffic access/impact study. A diverse array of local agency requirements and technical procedures currently exist for conducting such analyses. Under certain circumstances, a uniform
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The 5% has been chosen because thisproportion of a roadway's capacity causes a noticeable impact to mostdrivers. Guidelines that areappropriate for one specific area would undoubtedly fail to meet the needsof other communities. Finally, with that much new traffic, left- or right-turn lanes may beneeded to satisfactorily accommodate site traffic without adverselyaffecting through traffic. In general, TA/I studies are employed by localgovernments and, more specifically, by their engineering advisors andtransportation planning departments. They could, for example, includeany or some combination of the following considerations: "(1) currenttraffic problems in the local area such as a high-accident location,confusing intersection, or an intersection in need of a traffic signal; (2)the current or projected level of service of the roadway system adjacent tothe development, which will be significantly affected; (3) the sensitivityof the adjacent neighborhoods that may be perceived as impacted; (4) theproximity of existing or proposed site driveways to other driveways orintersections; (5) the ability of the adjacent, existing, or plannedroadway system to handle increased traffic, or the feasibility of improvingthe roadway system to handle increased traffic; and (6) other specificproblems or deficiencies that may be affected by the proposed developmentor affect the ability of the development to be satisfactorilyaccommodated."[11] Of course, the contents and extent of a TA/I study will depend to thelocation and size of the proposed development, as well as conditions in thesurrounding area. [2]F. In contrast, trip assignment shouldtake into account logical routings, available roadway capacities, leftturns at critical intersections, and projected or perceived minimum traveltimes. In addition, 1 additionalvehicles per hour can change the service level of an intersection approach. At times, this may help avoidembarrassing decisions and, possibly, legal battles. A diverse array of local agency requirements and technicalprocedures currently exist for conducting such analyses. Some important transportation system attributes include thefollowing: "(1) current and proposed street network, including functionalclassification, route jurisdiction, and the number of moving traffic lanes;(2) geometrics, especially at critical intersections, including such itemsas curb parking and potential street improvements; (3) intersection trafficcontrol; (4) signal timing and system operation at signalizedintersections; (5) existing or proposed site access points andconfiguration; and (6) existing and proposed rights-of-way."[13] Such information can subsequently be employed to estimate backgroundtraffic volumes. Before traffic patterns can be predicted and access improvementsdeveloped, the nature and function of these systems must be thoroughlyunderstood. Suchimprovements may involve transportation system management action. When the superior court held thatthe mall's impact on transportation beyond the town of Williston wasactually relevant to the permit process, the developer appealed to theVermont Supreme Court. [6]"Traffic Access and Impact Studies For Site Development," ITEJournal 58 (August 1988): 17. In cases where less than 1 new trips will be generated, certainother factors may also necessitate a TA/I study. [3]R. [9]"Traffic Access and Impact Studies For Site Development," ITEJournal 58 (August 1988): 18. Greenberg; M. With large developments, adetermination of travel mode may also be necessary. Forexample, common remedial measures often include the design and constructionof new roadways, intersections, and site driveways. Once a network database has beenassembled, MULATM provides quick answers to "what-if" type questions.Thus, it enables the transportation engineer to study traffic impact ofboth new traffic generators as well as traffic management schemes.[15] Traffic access/impact studies give authorities the ability to foreseepotential traffic and fiscal impacts. [12]J. The second step in TA/I analyses involves field surveys. Greenberg, Traffic Impact Analysis (Chicago, IL: AmericanPlanning Association, 1984), 1.----------------------- 1 [7]"Guidelines For Transportation Impact Assessment of Proposed NewDevelopment," ITE Journal 58 (June 1988): 39. [1 ]C. Secondly, the trafficvolumes for the various stages of a proposed development can be estimated.These may then be summed to obtain estimates of total future trafficvolumes. For instance,information regarding such factors as physical characteristics, actual siteuses, and land uses on adjacent properties might be described. Bibliography"A Guideline For Local Officials: Traffic Impact/Access Studies." ITE Journal 62 (July 1992): 44-45.Bonneson, J. It is essentialthat these analysts are able to forecast and the assess traffic needs ofboth developments and roadway transportation systems. D. More recently, computer programs have been developed which performTA/I analyses. [8]J. As with nonsite analyses, site traffic access/impact capacity studiesshould be performed for critical time periods. Krammes, "Travel Impact Evaluation For Major HighwayReconstruction Projects," Journal of Transportation Engineering 116(January/February 199 ): 64. The model assumes that individuals select trip routes based onperceived travel time (which is inferred from the average travel timesexisting when the trip is made). Traffic Impact Analysis. In considering the transportation components of a given development,transportation engineers initially must decide whether or not a trafficaccess/impact study is even needed. In general, the study area should include those roadwayson which at least 5% of the peak hour capacity will be composed of newtrips generated by the development. "Transportation Demand Management: Promise or Panacea?" Journal of the American Planning Association 59 (Summer, 1992): 327- 334.Greenberg, F.; Hecimovich, M. However,despite increasing demand for urban development, local governments areoften limited in their ability to fund infrastructure improvements such asroadway construction. [5]"A Guideline For Local Officials: Traffic Impact/Access Studies,"ITE Journal 62 (July 1992): 44. Hecimovich, Traffic Impact Analysis (Chicago, IL:American Planning Association, 1984), 1. Such systems as TRANSYT, and NETSIMsimulate traffic movements. Realistic estimates typically involve multiple paths betweenorigins and destinations. Taylor, "A PC-Based Method For Traffic Impact Analysis,"ITE Journal 57 (June 1987): 3 . During the 198 s, such factors led to widespreadconcern regarding the traffic impacts of various urban site developments.One method of determining whether or not a given area's roadway network cansupport a development's traffic is to perform a site traffic access/impactstudy. One ofthe first priorities for any study is to delineate its scope and extent.Local governments may, for example, want to establish the study's timehorizon. In general, this timeinterval involves the peak periods of both the project-related travel andthe area's transportation system. Mostimportantly, off-site roadway improvements should always be fullyintegrated with on-site recommendations. Under certaincircumstances, a uniform set of guidelines might prove useful. "A PC-Based Method For Traffic Impact Analysis." ITE Journal 57 (June 1987): 27-32."Traffic Access and Impact Studies For Site Development." ITE Journal 58 (August 1988): 17-24.----------------------- [1]Genevieve Giuliano. In order to enhance marketability, companiesmust ensure sufficient access to their site. In general, new trips generated by a proposed development should beassessed separately from nonsite traffic. Lothian, "Traffic Progression Assessment in TrafficImpact Studies," ITE Journal 61 (May 1991): 17. [15]M. Traffic Access/Impact Studies In many United States cities, traffic congestion has become a majorpublic policy issue. InOctober, 1978, the Pyramid Company of Burlington was granted a permit toconstruct a 9 -acre shopping center on a 1 -acre site near the town ofWilliston (6 miles ease of Burlington). Based on TA/I studies, however, aDistrict Environmental Commission overturned the local decision and deniedthe permit. Each development requiresdifferent degrees of analysis. Hence, traffic impactanalyses have become a "common prelude to development projects."[4] The actual evaluation of the transportation impacts of any givenproject should generally be performed by either transportation or trafficengineering professionals. In general,this reconnaissance evaluates site location and setting. In recent years, variouscircumstances have forced governing agencies to examine the impacts thatboth local developmental trends, as well as specific development proposals,will have on their locality's transportation system. These systems employ interactive graphics and CAD methodsin traffic modeling and planning. Whether of not suchneeds can be reconciled with a government's financial resources or even,possibly, its political consensus on infrastructure may determine whetheror not various projects are approved or disapproved. The problem ofreconstructing highways, while concomitantly accommodating large trafficvolumes, will surely prove difficult.[3] Such factors require that localauthorities understand the effects that both development and remedialaction will have on traffic flow. Inaddition, field surveys should also include an evaluation of long-rangecommunity development plans. Therefore, even if comprehensive proceduralguidelines for every possible TA/I study could be written, they wouldprobably require several volumes.[7] In general, the impact of new development is assessed with regard tothe deleterious effects that additional, site-related traffic has on theadjacent street system. For example, MULATM consistsof a "dense network". [13]"Guidelines For Transportation Impact Assessment of Proposed NewDevelopment," ITE Journal 58 (June 1988): 4 . In generalthough, these regions should generally contain 8 % or more of the trip endsthat will be attracted to the site. Projects may range fromfast-food restaurants to large-scale, mixed-use complexes (i.e.,office/commercial/residential buildings). The overall purpose of most TA/I studies is to demonstrate how thetraffic generated by a project will impact the surrounding area. Typically, TA/I analyses are projected over several years. Unfortunately for Pyramid, the supreme courtrefused to hear the appeal and the case was dismissed in June 1984.[16] Clearly, traffic access/impact studies serve an important function.By analyzing future traffic flows, they anticipate potential problems. Thus, the Highway Capacity Manual techniques areonly of limited utility in these analyses. Such circumstances have, at times, led toinconsistencies and disagreements with regard to how TA/I studies should beperformed, what elements should be addressed, and how the analyses shouldbe reviewed.[6] However, regardless of these problems, the creation of adetailed procedural manual for all traffic impact analyses in allcommunities would most certainly prove impractical. To approximate real world situations,trips start and finish along streets. Papacostas; P. S. Unwilling to pay forthe additional roadwork, the Pyramid Company appealed the commission'sfindings to the state superior court. In addition, averagevehicular delay is used to compute intersection approach delay. MULATM version 1.3 can process up to2 nodes and 6 links. [11]"Traffic Access and Impact Studies For Site Development," ITEJournal 58 (August 1988): 18. P. According to ITE Journal, "a completeTA/I study should be conducted whenever a proposed development willgenerate 1 or more additional (new) peak direction (inbound or outbound)trips to or from the site during the adjacent roadway's peak hour or thedevelopment's peak hour."[9] This level of traffic could be generated bythe following developments: (1) approximately 16 single-family homes; (2)22 -multifamily units; (3) 6 , square feet of general office space; or,lastly, (4) 1 , square feet of retail space.[1 ] There are severalreasons why a site trip generation threshold of 1 is appropriate. One recommended procedure for trip generation is as follows:"(1) check availability of local trip generation rates for comparablesites; (2) if time and funding permit, conduct trip generation studies atsites similar to the proposed development; (3) check national sources foran applicable range of trip rates; (5) determine the design level oftraffic to be utilized for the analysis and select appropriate rates; (6)determine any necessary adjustments that may be applied to account forspecific site characteristics; (7) select the most appropriate tripgeneration rates; and (8) if variation from normally recognized generationrates occurs, document the reasons why."[14] Upon estimating the total traffic into and out of the site, trafficmust be distributed and assigned to the roadway system. Prevedouros, Transportation, Engineering,and Planning, (Englewood Cliffs, NJ: Prentice Hall, 1987), 414-415. One example whereTA/I studies altered the course of a development occurred in Vermont. Moreover, not only are communities different, but the characteristicsof specific developments also vary considerably. This measurement typically reflects both thereduction in intersection traffic service and the diminished quality of thetraffic flow.[8] The impact is first quantified, and then mitigated. These boundariesmay be based on either "reasonable maximum convenient travel time" or,alternatively, result the presence of competing developments. S.; Prevedouros, P. In addition, planning software such as EMME/2,QRS II, TRANPLAN, and MULATM perform complex analyses involving theevaluation of different traffic alternatives. P. Additionally, any potential futurechanges in peaking characteristics should be assessed; this might beparticularly relevant in growing areas. Chicago, IL: American Planning Association, 1984."Guidelines For Transportation Impact Assessment of Proposed New Development." ITE Journal 58 (June 1988): 39-41.Krammes, R. Thirdly, inaddition to dramatically affecting communities, large-scale development canalso have major regional effects.[2] Finally, in the near future, theUnited States government may undertake major highway reconstructionprojects in urban areas throughout the country. Also, weekend and off-peakconditions must be reviewed. Lastly, in areas where less than 5% of traffic is generated bythe site, the study should at least include adjacent intersections and allknown congested locations. Theinfluence of a series of traffic signals on traffic progression must beassessed directly. In this system, network links and nodes are used torepresent streets and intersections. Trip destinationanalysis, or trip distribution, results in origin-destination tripestimates; whereas, trip assignment determines which access routes betweenorigins and destinations will be used by the site traffic. These analyses should provide an indicationof both the type and direction of a community's future development. For example, a key component of the signalized intersectionanalyses is average vehicular delay. From these calculations, the Highway CapacityManual techniques may provide an estimation of through-traffic servicelevels for both urban and suburban signalized arterioles.[12] Unfortunately though, the current Highway Capacity Manual methodologyfor the calculation of service levels requires field observation. Luh; W. Prior to tripdistribution, a site influence area should be defined. Theactual selection of years, however, should be related to such factors aslocal transportation plan horizons, development phasing, or predicted majortransportation system changes. These volume estimates should then be adjusted to representpeak periods (i.e., the peak hour of the peak day of an average week of theyear). Inevitably, such advances willlead to enhanced planning ability, increased traffic design quality, and,ultimately, better transportation systems. Based upon this figure, thetechniques determine intersection level of service. Perhaps, inthe future, standardization will come in the form of computerized trafficaccess/impact studies. Ingeneral, the analyses should provide information on the following points:(1) existing traffic conditions; (2) additional traffic that will begenerated by the development; (3) effects that the additional traffic willimpose on the existing conditions; and (4) the types of remedial measuresor site plan changes that will minimize the traffic effects of the proposeddevelopment.[5] Access/impact studies tend to vary depending on both the varioustraffic issues of each individual community and the different trafficvolumes generated by each specific development. Forone, 1 vehicles per hour represents approximately 15% of the curb travellane capacity under signalized control. [16]F. Bonneson, "Traffic Volume Adjustments For Impact Analysis," ITEJournal 57 (April 1987): 43. Alternative modes maybe evaluated with regard to their attractiveness. Some localities haveadopted study standards that are only applicable to the characteristics oftheir particular community. Different destinations may varyaccording to the type of development, competing developments, developmentsize, and the surrounding environment. Forecasted nonsite volume consists of through traffichaving neither an origin nor a destination within the site of the proposeddevelopment. Actual site impacts may be measured using the procedures delineatedin the 1985 Highway Capacity Manual. This methodology helps transportationengineers determine the degree of deterioration on the surrounding roadwaysystem in terms of "level of service." The operation/design techniques areuseful in the analysis of freeway ramps and weaving sections; whereas, theplanning analysis is most appropriate for assessing signalizedintersections. A. For the most part, TA/I capacity studiesshould include all critical intersections and access points during peaktraffic periods. In contrast, most TA/I studies evaluate future roadwayand traffic conditions. Furthermore, most large-scale developmentsignificantly alters a community's transportation environment. Transportation, Engineering, and Planning. D. Asthe use of computers in these analyses becomes more widespread, TA/Istudies should only become more accurate. Eventually, these various analyses may result in recommendations.These generally may be subdivided into four general categories: (1)regional or subregional network improvements; (2) improvements adjacent tothe site; (3) site access improvements; and (4) program changes. Englewood Cliffs, NJ: Prentice Hall, 1987.Taylor, M. Inparticular, existing and proposed transportation systems need to beassessed. These tend to relate tolocal safety or capacity deficiencies. In certain cases, for example, it may bediscovered that traffic improvements are required. Moreover, it has been designed to distinguishbetween different classes of roads, various intersections control types,intersection lane configurations, and intersection turning and throughmovements. [4]"A Guideline For Local Officials: Traffic Impact/Access Studies,"ITE Journal 62 (July 1992): 44. A. For example, the TA/I indicatedthat the project would require improvements and road construction at threespecific sites outside of Williston's jurisdiction. One important tool for delineating these concerns is the trafficaccess/impact (TA/I) study. These critical intersections may include the following:(1) major intersections within a specified area; (2) all intersectionswhere increases in traffic volume might create a need for improvements; and(3) all intersections that might have to operate below their design levelsof service. "Traffic Volume Adjustments For Impact Analysis." ITE Journal 57 (April 1987): 43-46.Giuliano, G. Additionally, TA/I analyses may alsoprove useful to developers. For example,different opinion surveys have demonstrated that urban residents often ranktraffic as one of the major problems faced by their community.[1]Moreover, local governments have become increasingly aware of the fact thattheir existing transportation networks are deteriorating. A typical TA/I might, for example, evaluate the construction of alarge shopping center in an area of significant traffic congestion. Many of the district commission's reasons for the actioninvolved the project's traffic impacts. "Traffic Progression Assessment in Traffic Impact Studies." ITE Journal 61 (May 1991): 17-21.Papacostas, C. These individuals should have both specifictraining in traffic and transportation engineering, as well as severalyears of experience in the preparation of traffic studies. Roadway space is a valuable commodity. "Transportation Demand Management: Promise orPanacea?" Journal of the American Planning Association 59 (Summer, 1992):327. When thisnumber is added to the running time between two signals, average travelspeed can be estimated. Finally, it is important that, giventransportation system characteristics and trip distribution, trafficvolumes appear logical. "Travel Impact Evaluation For Major Highway Reconstruction Projects." Journal of Transportation Engineering 116 (January/February 199 ): 64-8 .Luh, J.; Lothian, W. [14]"Traffic Access and Impact Studies For Site Development," ITEJournal 58 (August 1988): 2 .
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