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Trip Generation Tool for Mixed-Use Developments

Research has consistently shown that neighborhoods that mix land uses, make walking safe and convenient, and are near other development allow residents and workers to drive significantly less if they choose. In fact, research has found that in the most centrally located, well-designed neighborhoods, residents drive as little as half as much as residents of outlying areas. 1Along with these benefits, mixed-use development can improve communities in other important ways, including supporting affordable housing by lowering transportation costs. 2Studies have also shown that mixed-use development, especially in concert with other smart growth strategies, provides significantly higher returns to local governments through property and sales taxes 3while requiring lower per unit infrastructure and public-service costs. 4The typical development planning and approval process treats mixed-use developments as if the uses were separated and only accessible by car, leaving mixed-use developments at a disadvantage compared to conventional, single-use development. Recognizing the lower traffic impacts of mixed-use development in central, well-connected neighborhoods in the planning and approvals process would help communities reduce traffic and realize other benefits.

The technical methods to estimate how much traffic a new development will create, known as trip generation analysis, have been standardized by the Institute of Transportation Engineers (ITE) and are used by traffic engineers across the country. However, these methods are generally based on data collected from single-use, automobile-dependent, suburban sites. They do allow for some internal capture (trips that might be entirely within larger, mixed-use developments), but in general the methods do not adequately account for the effects of compact development, mix of uses, site design, walkability, transit, and regional accessibility – key elements of smart growth strategies and of a sustainable community.

To help provide communities with better tools to analyze new development, EPA, in cooperation with ITE, worked with leading researchers and practitioners to develop new data and methods to estimate the trip-generation impacts of mixed-use developments. EPA analyzed six metropolitan regions, merging data from household travel surveys, GIS databases, and other sources to create consistent land use and travel measures. The resulting linked models estimate internal capture of trips within mixed-use developments as well as walking and transit use for trips starting or ending in mixed-use developments. The models have been validated against actual traffic counts at mixed-use developments across the country. The method is currently used in several regions in California, Washington state, and New Mexico, and the Virginia Department of Transportation recently adopted it as a statewide standard for determining the traffic impacts of urban developments.

The EPA team put the models into a spreadsheet tool that makes it easy for local government staff, consultants, and developers to estimate trips generated by a new mixed-use development. The spreadsheet estimates vehicle trips in the peak periods and for an entire day. The method also predicts trips by walking and transit and estimates the daily vehicle miles of travel associated with the development. The tool requires information about the development site and its surrounding area, including geographic, demographic, and land use characteristics. It also includes default national parameters for trip generation but allows the use of local values if available. An associated report describes the analytic basis for the method and the data used to calibrate and validate it. It is available upon request.

santana row

Santana Row in San Jose, California, reduces trip generation by mixing uses in a walkable neighborhood on the site of an old shopping mall

The following resources give more information on development and testing of the method and San Diego's use of the tool:

market common

Mixed-use developments like Market Common in Arlington, Virginia, generate fewer vehicle trips than conventional, single-use development, especially if located in a walkable neighborhood close to transit service.

The following resources describe the standard trip generation methods and other recent efforts to better understand the impacts of mixed-use developments and related smart growth strategies:

For more information, please contact John Thomas (202-566-1285, thomas.john@epa.gov) or Christopher Forinash (202-566-0518, forinash.christopher@epa.gov).

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