Researchers expand trip generation to include people walking, biking and riding transit


A new NITC report offers a multimodal framework for transportation impact analysis – a welcome tool for professionals in many cities seeking more detailed data about non-drivers.

Improving Trip Generation Methods for Livable Communities, a research project headed by Kelly Clifton of Portland State University and Nico Larco of the University of Oregon, is the latest effort in an ongoing collaboration to create more open sourced, widely available data about non-motorized road users.

Over the last decades, cities have become more invested in fostering the conditions to support walking, biking and public transit.

The land development process presents a unique challenge.

Prior to a zoning change or new development, someone has to determine what its impact on the transportation system will be, and whether upgrades will be necessary to accommodate travelers to the new destination. Trip generation is the first step in the conventional transportation forecasting process.

Current trip generation methods used by engineers across the country tend to focus on motorized modes.

Without reliable trip generation rates for anyone but drivers, the transportation impact is difficult to predict. Certain land uses will draw far more walkers, cyclists and transit riders than drivers.

Thus, cities lack enough information to create planning and design requirements that support non-automobile modes, and to create spaces that will meet the needs of the people who want to use them.

In previous research, Clifton examined contextual influences on trip generation such as the surrounding built environment and urban density, employing a method which has since made its way into the ITE handbook.

She has also looked into the connections between consumer behavior and travel modes. She cautions not to lose sight of sociodemographic factors, but to remember to put the user in “land use.”

“One establishment may fill different needs for different people, and the social context matters as much as the built environment,” Clifton said.

A failure to account for the characteristics of site visitors or the potential market for businesses can lead to large errors in the estimation of the number of trips.

The research has shown that seemingly similar land uses can have very different travel outcomes, even within the same type of area, because the users interact with the site activity in different ways.

“We are challenged to define land use in a way that considers the nature of human activities and interactions on the site, has a strong theoretical link to travel behavior, places the end-user at the center, does not over-prescribe, and allows for flexibility and re-classification over time. This is a tall order, and more research will be needed to frame and develop such a methodology,” Clifton said.

This latest project offers critical tools for planners and practitioners, including an approach for site-level and area-wide analysis.

For more details, visit the project page or download the final report.

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