Smart Growth Trip Generation

Objective: The goal of this project is to develop and disseminate data and a method that practitioners can use to estimate multimodal trip-generation rates for “smart growth” land use development projects proposed in California. These include projects located in downtowns and other urban areas served by transit service and in which a variety of land uses are close enough to allow walking or bicycle travel. An acceptable method is needed to estimate trip-generation for transportation impact analyses/studies of “smart growth” projects, which agencies typically require to estimate the impacts of proposed projects and identify improvements to help “mitigate” impacts.

Need: The first step in preparing a transportation impact analysis is to estimate the number of trips by cars, trucks, and other modes of travel that may result from a proposed land use project – which is commonly referred to as “trip-generation.” Currently, practitioners typically obtain trip-generation rates published by the Institute of Transportation Engineers (ITE), a national professional organization. This data is collected primarily at suburban sites without significant transit, bicycle, or pedestrian facilities and is available only for vehicles, not for “active” modes such as walking, bicycling, or transit. However, recent studies indicate that such data often significantly over-estimates the number of trips from cars and trucks for land use projects located in urban areas near transit and within easy walking distance of other land uses – in fact, ITE guidelines state that their trip-generation rates data should not be used for land use projects in such locations. However, there is currently no method, tool, or data available in the U.S. to estimate trip-generation rates for such projects. This makes it extremely difficult to accurately estimate the transportation-related effects of such projects, or to implement appropriate multi-modal “mitigation measures” for people who may walk, bike, drive, or use public transit to travel to/from such sites.

Results: With ongoing input from a technical advisory Panel, UC Davis researchers collected trip-generation data at 30 smart growth land uses in California. They then used this information, along with trip-rates data from other studies, to develop a method embedded in a spreadsheet tool that can be used to adjust available trip-generation rates for “smart growth” land use projects proposed in California.

Products: This project produced a Final Overview Report with several technical Appendices; and a Tool to implement the Smart Growth Trip-Generation Adjustment Method: