Research Program Area: Climate Change
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.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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