Trip Generation Rates for Transportation Impact Analyses of Infill Developments (2013)

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N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 758 Trip Generation Rates for Transportation Impact Analyses of Infill Developments James M. Daisa Kimley-Horn and associates, inc. Pleasanton, CA Michael Schmitt Kimley-Horn and associates, inc. Sacramento, CA Peter Reinhofer V3 companies Woodridge, IL Kevin Hooper KeVin Hooper associates Falmouth, ME Brian Bochner texas a&m transportation institute College Station, TX Luke Schwartz Kimley-Horn and associates, inc. Pleasanton, CA Subscriber Categories Highways • Economics • Planning and Forecasting TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2013 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP REPORT 758 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Lawrence D. Goldstein, Senior Program Officer Anthony P. Avery, Senior Program Assistant Eileen P. Delaney, Director of Publications Doug English, Editor NCHRP PROJECT 8-66 PANEL Field of Transportation Planning—Forecasting Terry L. Parker, California DOT (retired), Sacramento, CA (Chair) Kelly J. Clifton, Portland State University, Portland, OR Steven A. Smith, San Bernardino Associated Governments, San Bernardino, CA Lisa M. Fontana Tierney, Institute of Transportation Engineers, Washington, D.C. Ed J. Christopher, FHWA Liaison Kimberly Fisher, TRB Liaison

F O R E W O R D By Lawrence D. Goldstein Staff Officer Transportation Research Board NCHRP Report 758: Trip Generation Rates for Transportation Impact Analyses of Infill Developments provides an easy-to-apply process for use by transportation professionals when estimating vehicular trip generation in built-up urban areas, incorporating the effects of site-specific, local, and area-wide land use and transportation characteristics on esti- mates of vehicular trip generation for proposed infill development. This process is based on the development and application of mode share and vehicle occupancy adjustment factors applied to conventional trip generation estimates using rates published by the Institute of Transportation Engineers (ITE). The study details two ways of deriving the adjustment fac- tors: (1) collecting empirical data from proxy sites located in environments that represent the future context of the project being analyzed, and (2) extracting factors from household travel surveys. The product of this research includes two components: (1) a final report that documents the background, research approach, the development and application of methods to esti- mate infill trip generation, and a recommended verification approach; and (2) a supple- mental technical report that details the application of the household travel survey method. The combination of these two components offers a comprehensive analytical approach and a detailed set of application techniques and requirements to estimate infill development trip generation. New development and redevelopment projects located near, or surrounded by, existing land uses are often termed urban or suburban “infill.” Appropriate development and rede- velopment in such areas are important strategies for revitalizing the nation’s aging city and suburban cores, increasing efficient and cost-effective use of existing infrastructure (includ- ing streets, transit, and utilities), and expanding opportunities for housing, recreation, and economic growth in affected areas. During local land use review and development permit- ting processes, public agencies commonly require estimates of vehicle travel impacts associ- ated with proposed land use projects, assessments of their potential contribution to traffic congestion, and identification of appropriate mitigation strategies. Common mitigation strategies include impact fees, proffered private developer contributions, special tax assess- ment districts, and specific facility improvements—all of which have the potential to affect the financial parameters that underwrite proposed new development. Many agencies and jurisdictions are prioritizing the development of these infill, mixed- use, and transit-oriented-development (TOD) projects. In response, the need for improv- ing and refining trip generation estimation methods applicable to an urban context is of increasing interest and importance. The process proposed as an outcome of this research is specifically designed for use by members of the transportation planning and traffic engi-

neering profession who prepare and review site transportation impact analyses (TIAs). This group of users will appreciate the fact that the method builds on conventional techniques and resources with which they are familiar, not requiring a significant investment in time devoted to learning new techniques. In developing traffic and transportation impact analyses for urban and suburban infill projects, professionals have often relied on ITE published trip generation rates for various types of land use. The ITE data, however, are predominantly representative of suburban contexts and their automobile-dependent land use patterns and transportation networks and typically do not take into account variations in type and location (suburban versus urban) of proposed land uses, proximity of transit service, and the existence of pedestrian and bicycle facilities. The common use of suburban-focused vehicular trip generation data in the preparation of TIAs, combined with a lack of information and techniques on how and when to adjust the data, has often resulted in an application of conventional trip generation rates to proposed infill development, even in places that are compact, highly walkable, and transit-rich. This use of conventional data can overpredict vehicular traffic impacts, result- ing in possible mitigations that negatively affect use of transit, bicycle, and pedestrian facili- ties in the infill project area. Inaccurate data may also result in excessive traffic mitigation fees or requirements for additional infrastructure that can hinder the type of development that promotes lower automobile use. Applying the methods presented in this report will contribute to a greater understand- ing of transportation characteristics of infill development, providing transportation engi- neers, public transit professionals, city planners, and decision makers with the facts they need to plan and implement infill development effectively. The research offers a systematic and methodical procedure for analyzing potential traffic impacts in urban and urbanizing locales. In support of this process, agencies seeking a consistent and uniform procedure for analyzing infill development in their community can develop and validate a local database of infill trip generation rates by sponsoring local infill trip generation studies (using the proxy site method) or extracting region-specific travel data to develop local infill trip rates (using the household travel survey method). Validating the output of the methodology presented in this research is important; how- ever, the research concluded that a definitive validation required more resources than were available. The validation process demonstrated that the proposed method produces consis- tently lower estimates of infill trip generation, ranging from ½ to ²⁄³ of estimates based on conventional data—a finding that is consistent with other research. Based on this remain- ing need, the study concludes with specific recommendations for future research on the travel characteristics of infill development and the identified need for a commitment by the transportation profession to contribute empirical data for a more complete and definitive validation of the methodology.

C O N T E N T S 1 Summary 3 Chapter 1 Background 3 1.1 Problem Statement 3 1.2 Research Objective 3 1.3 Scope of Study 5 Chapter 2 State of the Practice 5 2.1 The Importance of Trip Generation 5 2.2 Defining Infill Development 6 2.2.1 Survey of Professional Organizations 6 2.2.2 Literature Review of Infill Development Definitions and Context 6 2.2.3 Definition of Infill Development 6 2.3 Current Infill Trip Generation Practices 7 2.4 Research in Estimating the Trip Generation of Infill Development 7 2.5 Trends in Estimating Trip Generation 10 2.6 Summary and Conclusions on the State of the Practice 11 Chapter 3 Research Approach 11 3.1 Basis for Selecting an Approach 12 3.2 Selection of an Approach and Conclusion 15 3.3 Summary and Conclusion 17 Chapter 4 Development and Application of Methods for Estimating Infill Trip Generation 17 4.1 Overview of Approach 18 4.2 Proposed Methodology 18 4.3 Application of the Proxy Site Method 22 4.4 Developing Adjustment Factors for the Proxy Site Method 22 4.4.1 Baseline Adjustment Factors 23 4.4.2 Guidelines for Selecting a Proxy Site 23 4.4.3 Infill Adjustment Factors 24 4.4.4 When to Use Proxy Site Method Variants 24 4.4.5 Considerations for Site Impact Analysis Planning Horizons 24 4.5 Application of the Household Travel Survey Method 25 4.5.1 Required Data for the Household Travel Survey Method 26 4.6 Data from the San Francisco Bay Area 26 4.6.1 Variables in the Household Travel Survey Method 27 4.7 Procedure for Applying the Household Travel Survey Method 27 4.7.1 Determining Context 27 4.7.2 Transit Type, Frequency, and Proximity 27 4.7.3 Other Criteria 27 4.7.4 Selecting the Geographic Units of Data

28 4.7.5 Extracting Mode-Share Adjustment Factors 29 4.7.6 Estimated Mode Share by Land Use 29 4.7.7 Estimated Vehicle Occupancy Adjustment Factors 30 Chapter 5 Confirming the Proposed Approach for Estimating Infill Trip Generation 31 5.1 Selecting a Method for Verification 31 5.2 Verifying the Travel Survey Method: A Case Study from Metropolitan Washington, D.C. 31 5.3 Application of the Method and Results of the Verification 31 5.3.1 Expected Results of the Case Study Analysis 32 5.3.2 Summary of Findings 32 5.4 Derived Adjustment Factors 32 5.4.1 Residential Land Use Category 33 5.4.2 Office Land Use Category 34 5.4.3 Retail and Restaurant Land Use Categories 35 5.5 Application of the Approach Using Data from the San Francisco Bay Area Household Travel Survey 35 5.5.1 Findings and Overall Conclusions of the Analysis 37 Chapter 6 Conclusions and Recommendations 37 6.1 Principal Conclusion 38 6.2 Additional Conclusions 38 6.3 Future Research 40 Notes and Citations 42 Appendix A Predominant Characteristics of Context Zones 1 Supplemental Technical Report Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.