Assessment of Options for Quantifying Reduction in Vehicle Miles Traveled (VMT) from Mitigation Measures

Guidelines for the California Environmental Quality Act require the mitigation of projected increases in vehicle miles traveled (VMT) stemming from highway expansion projects. Quantifying the likely effects of proposed mitigation measures enables an assessment of the degree to which the mitigation program offsets the estimated increase in VMT for a project. The purpose of this report is to provide an overview of possible estimation methods for 45 mitigation strategies and recommendations on the most appropriate method for estimating the reduction in the number of miles of vehicle travel that could be expected to result from the implementation of a specific measure. The methods take into account the extent of the measure but may not account for the specific context. In general, two types of methods are available: travel demand forecasting models, and effect-size approaches. For several measures, this report concludes that the reduction in VMT cannot be estimated based on the available evidence. The Evidence Assessment Report provides as assessment of the strength of the evidence for each of the measures (Handy et al., 2024).