A tool to estimate the added VMT from highway expansions

By Michael Brenneis and Eric Sundquist

Since passage of S.B. 743 in 2013, California agencies have wrestled with questions around the added travel and emissions resulting from land use and transportation projects. On the land use side, see SSTI’s recent webinars about land-use review reforms in San Jose and Pasadena.

On the transportation side, there is new information available as well, addressing the relationship between lane-miles and vehicle-miles traveled (VMT). The National Center for Sustainable Transportation (NCST) has developed an induced travel demand calculator designed to calculate the percentage of additional annual VMT when highways are widened. The tool, calibrated for California counties and regions, accepts some simple variables: the highway type, the location of the facility, and the number of lane miles the project will add. It returns the induced annual VMT that would result from the widening.

The tool bases this estimate data for the current number of lanes miles and annual VMT in the location, as well as literature-based capacity-to-VMT elasticities. More information about the calculator and its inputs and assumptions can be found on the calculator’s information page.

Since the underlying data was collected only in California, and collected before many toll or high-occupancy vehicle lanes were added, the NCST says the tool is only applicable to general purpose or car pool lane-mile additions. The tool cannot be used to estimate VMT change due to lane conversion to high occupancy toll use or lane elimination.

Other methods for estimating VMT effects from capacity expansion exist, including one by SSTI that estimates VMT using accessibility and household demographic data.

Michael Brenneis is an Associate Researcher at SSTI.

Eric Sundquist is Director of SSTI.