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3 This chapter discusses the rationale for undertaking this research study, presents the studyâs objective, and summa- rizes the three major work activities that formed the basis of this study. 1.1 Problem Statement In the United States, the Institute of Transportation Engi- neersâ (ITE) Trip Generation Manual (3) is the primary source of data and methods for estimating vehicle trips in the per- formance of traffic impact analyses. The ITE Trip Genera- tion Manual was first published in 1976 and is now in its ninth edition. The manual has undergone several updates that have included the addition of new land uses, land-useâ specific refinements resulting from additional data collec- tion, and revised and expanded estimation methodologies. The majority of the data included in the ITE Trip Generation Manual is based on automobile counts conducted at single- use, suburban, and exurban sites with limited pedestrian, bicycle, and transit activity. Although this resource is com- monly accepted as valid for sites in the contextual settings from which the data were collected (i.e., suburban and exurban communities), it is less easily applied to urban and urbanizing sites with moderate to extensive pedestrian, bicycle, and transit activity. Suburban and urban sites commonly have important dif- ferences in trip generation that result from their localized circumstances, such as zoning ordinances that segregate uses, the diversity and mix of land use types, site design, density, and the availability of multimodal transportation options. Accord- ingly, the data on which most of the land uses in the ITE Trip Generation Manual are based are not directly applicable to more urbanized uses. Irrespective of these limitations, the ITE Trip Generation Manual is still the principal resource for estimating the trip generation of developments located in contexts not repre- sented by the underlying data. In these cases, preparers of traf- fic impact analyses may choose to adjust ITE trip generation rates using local factors or other published sources of informa- tion to better reflect the local circumstances. However, many choose, or are required, to use the rates directly from ITE with- out modification. Given that many agencies and jurisdictions are prioritiz- ing the development of infill, mixed-use, and transit-oriented development (TOD), the refinement of trip generation meth- ods and data for urban contexts is of increasing interest. Within the transportation profession, there have been several note- worthy efforts to advance this area of practice and its underly- ing research. However, among practitioners there is still not a commonly accepted best-practice approach to trip generation for developments in urban contexts. As such, there is the con- tinuing need to provide transportation professionals credible trip generation methods to better assess the impacts and ben- efits of infill development. 1.2 Research Objective This research study responds to the challenges experienced by public agencies and practitioners in evaluating traffic impacts of development or redevelopment projects located in areas that are substantially built up. This type of development, often called infill development, occurs in urban and adjacent tran- sitional areas. The overall objective of this research was to develop an easily applied methodology to estimate automo- bile trip generation and mode share of non-vehicular trips that can be used in the preparation of site-specific transpor- tation impact analyses of infill development projects located within existing higher-density built-up areas. 1.3 Scope of Study This study was divided into multiple tasks, each of which was detailed in working papers reviewed by a research panel of peers from the transportation profession. These tasks were C H A P T E R 1 Background
4carried out over the course of the following three major work activities: 1. The state of the practice and current research on methods for estimating and using trip generation in determin- ing transportation impacts of proposed infill develop- ment were assessed. Identified trip estimation methods were subsequently categorized into discrete candidate approaches and evaluated to determine their ability to meet the research objective. Based on the outcome of this analysis, an approach for estimating infill trip generation was selected. 2. The selected approach and the information gained from evaluating alternative approaches were used as a founda- tion for proposing a method consistent with the require- ments, resources, and capabilities normally available for preparing transportation impact analyses. 3. The sources for obtaining or collecting required input data were identified, and the validity of the proposed method was evaluated. The research panel actively participated in the review and evaluation of study progress and provided direction for data collection and analysis elements of the study.