California Air Resources Board

Principal Investigator/Author: Michael Anderson

Contractor: University of California, Berkeley

Contract Number: 18RD022

Project Status: Completed

Relevant CARB Programs: Climate Change, Greenhouse Gas Emission Inventory Program

Topic Areas: Greenhouse Gas Inventory, Greenhouse Gas Monitoring Network, Sustainable Communities, Transportation

Research Summary:

This project uses Caltrans Performance Measurement System (PeMS) data from four study sites in northern and southern California to estimate the effects of non-general-purpose lane capacity expansions on traffic flows. These effects, often referred to as "induced travel," are critical in determining the environmental impacts of transportation infrastructure projects and forecasting regional changes in vehicle miles traveled (VMT). While a number of studies estimate correlations between aggregate miles of roadways and total VMT, these results are not directly applicable to most current and future California roadway capacity projects, since non-general purpose lane expansions, including high-occupancy vehicle (HOV) and high-occupancy toll (HOT) lanes, are becoming an increasingly common strategy for expanding capacity on congested freeways.

The results indicate statistically significant increases in average speeds and traffic flows at all four study sites. The increases tend to be larger during peak hours, though increases are documented in most cases during both peak and off-peak hours. The report also presents results from a set of "placebo tests" using data from locations without lane expansions for comparison purposes. These estimates reflect short-run local impacts and do not speak to medium- or long-run effects, spillovers to arterial street networks, regional impacts, or land use changes. This research fills a critical gap in the existing induced travel research by evaluating short-term, project-level induced travel results specific to non-general-purpose lane expansion that was previously missing.

Keywords: PeMS, lane, traffic, induced travel, transportation, vehicle miles traveled (VMT)