Contextual Influences on Trip Generation

Performed in conjunction with Portland Metro Regional Council and the local community partners, the Contextual Influences to Trip Generation project aims to reassess local trip generation rates for common uses, grocery stores and restaurants, at various locations in the greater Portland region. The data collected from this study will be used to develop consistent regional trip rate reductions reflective of the local context, considering proximity to transit, employment or residential density, and other factors of urban form.


Have you been asked to participate in this survey? Has your business been selected for this study? Find responses to frequently asked questions for participants or businesses.

For more specific questions, contact the Principle Investigator, Dr. Kelly J. Clifton of Portland State University at

Traditionally, the Institute of Transportation Engineers (ITE) Trip Generation Manual has provided guidance in accounting for the vehicle trips generated at new or renovated development sites. However, the rates provided have been representative of behavior typically present in low-density, single-use lots with little or no transit access, or bike and pedestrian facilities. Because of this, there are many barriers toward justifying lower trips generated by sites located in more urban, mixed-use or multi-modal locations.

This research proposes to develop multi-modal trip generation rates that better reflect the relationship between land use, transportation and travel demand for specific land use types located in various contexts. The project aims to collect local data (using multi-modal counts and establishment surveys) on specific land uses to develop trip generation rates that are sensitive to demographic, land use and transportation contexts.

By participating in this study, businesses are contributing by helping Portland Metro and the community partners provide more informed, consistent and validated trip generation policies in our local contexts. In turn, the information found from this research will simplify the justification process involved in adapting trip rate reductions for these common land uses in areas where trip generation rates tend to be lower than traditional ITE rates. In addition, by applying more accurate estimations of trip reductions due to multi-modal contexts, future developments and renovations may see additional impact fee reductions from the reduced number of trips generated. As this contextual problem with ITE Trip Generation Rates is not restricted to just the Portland area, we hope to broaden the scope of our research to reach out to other communities with this similar problem across the country in addition to providing community partners and Metro with the findings from this study.