Review of the Travel Demand Model Benchmarking Method Used to Estimate Induced VMT for the I-680 Express Lane Project

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. One of the early efforts to use benchmarking is the induced VMT analysis completed for the I-680 Northbound Express Lane Completion Project’s Draft Environmental Impact Report/Environmental Assessment. The authors review and assess the benchmarking method used for the I-680 project. They find that the method yielded significantly greater induced VMT estimates than the non-benchmarked TDM, but the estimates were still 32% to 54% lower than the California Calculator’s estimates. More broadly, the authors find that benchmarking can yield similar induced VMT estimates to the elasticity-based estimation methods, and also has the added benefit of producing VMT outputs in a format (e.g., VMT by speed bins) that can be readily used as inputs to analyses of related impacts (like greenhouse gas and local air pollutant emissions). However, for purposes of TAF compliance, benchmarking methods should be carefully examined to ensure that they are, in fact, yielding similar induced VMT estimates to the California Calculator.