The National Center for Sustainable Transportation’s (NCST’s) Induced Travel Calculator (Calculator) has generated substantial interest among policymakers and practitioners as a method for estimating induced vehicle miles traveled (VMT). With Calculator use increasing, the Institute of Transportation Studies at University of California, Davis (ITS-Davis) initiated a project to update the Calculator and improve its functionality based on recent data and empirical research. Efforts included adding three more years of baseline VMT and lane mile data to the Calculator (2017, 2018, and 2019), adding ranges to the Calculator’s induced VMT estimates (+/-20%), and providing an updated review of the induced travel literature. The team also investigated and determined that there is not enough empirical evidence to justify using different elasticities based on initial congestion levels, urban versus rural setting, or lane type (for general-purpose lanes, high-occupancy-vehicle lanes, and high-occupancy toll lanes). Going forward, this report suggests avenues for future induced travel research, including meta-analyses of induced travel studies to estimate pooled effect sizes, more research on the impact of existing traffic congestion and other contextual factors on induced travel effect size, and further studies on induced travel from managed lanes. It will also be important to continue monitoring other induced travel calculators for consistency with NCST’s Calculator.
