UC Davis Institute of Transportation Studies

California policy has slowly shifted to require analysis of the “induced travel” effect – the phenomenon whereby increasing roadway capacity increases vehicle miles traveled (VMT). For example, the California Department of Transportation’s (Caltrans’) Transportation Analysis Framework (TAF) requires analyzing the induced VMT effects of projects on the State Highway System as a part of the environmental review process. Because effectively no TDM currently used in California can pass the TAF’s checklist for model adequacy for estimating project-level induced VMT, agencies must often choose between estimating induced VMT using either the California Calculator – a web tool that is based on empirical evidence of the induced travel effect – or employ a hybrid approach, where the applicable TDM is benchmarked to the California Calculator’s induced VMT estimates. Eschewing both of those TAF-recommended options, the Los Angeles County Metropolitan Transportation Authority proposes two hybrid approaches, one for program-level induced VMT estimation and one for project-level estimation. The authors review both methods. They find that neither approach is theoretically justified or supported by the weight of the empirical evidence. More broadly, because TDMs are limited in their ability to accurately and reliably estimate induced VMT, the other two approaches suggested in Caltrans’ TAF – using the California Calculator or benchmarking a TDM to the calculator’s induced VMT estimates – are more reasonable alternatives.