The National Academies

NCHRP 08-66 [Completed]

Trip-Generation Rates for Transportation Impact Analyses of Infill Developments

  Project Data
Funds: $300,000
Research Agency: Kimley-Horn and Associates, Inc., with Texas Trans[portation Institute, Kevin Hooper Associates, and Data Smarts
Principal Investigator: James M. Daisa
Effective Date: 4/4/2008
Completion Date: 11/1/2013


New development and redevelopment projects located near, or surrounded by, existing land uses are often termed urban or suburban “infill.”  Appropriate development and redevelopment 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 (such as streets, transit, and utilities), and expanding opportunities for housing, recreation, and economic growth in such areas. 

During local land use review and development permitting processes, public agencies commonly require estimates of vehicle travel impacts associated with proposed land use projects, assessments of their potential contribution to traffic congestion, and identification of appropriate mitigation strategies.  These strategies often include mitigation fees, proffered private developer contributions, special tax assessment districts, and specific facility improvements. 

In developing traffic and transportation impact analyses, professionals often rely on the Institute of Transportation Engineers’ (ITE) published trip-generation rates for various types of land uses; however, it may not be accurate to use currently available trip-generation rates to analyze traffic impacts associated with proposed infill land use projects.  Such data typically does not take into account variations in type and location of proposed land uses, the availability and proximity of transit service, and the existence of pedestrian and bicycle facilities.  Applying available trip-generation rates to proposed urban or suburban infill development projects that have transit or good pedestrian access can over-predict vehicular traffic impacts. 

The consequences of over-estimating vehicle trips can lead to recommendations for excessive traffic mitigation fees and infrastructure improvements, leading to possible neighborhood opposition (and sometimes costly and time-consuming lawsuits).  This process can also result in demand for more parking spaces than may actually be needed to support the proposed development.  Over-estimating mitigation can, in turn, result in higher development costs as well as delay and even cancellation of otherwise beneficial infill projects—impacts that can stall economic development and the provision of needed housing and job growth within existing urban and suburban redevelopment areas.  As a result, research is needed to help better understand trip-generation characteristics of infill development. 

The objective of this research was to develop an easily applied methodology to prepare and review site-specific transportation impact analyses of infill development projects located within existing higher-density urban and suburban areas.  For the purposes of this study, “methodology” referred to trip-generation, modal split, and parking generation. The methodology addresses both daily and peak-hour demand for all travel modes.

Status:  The Final Report has been completed and released as NCHRP Report 758.

To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=1616