Measuring What Matters: Promise and Pitfalls of Off-Site Vehicle Miles Traveled Evaluation and Mitigation for Environmental Review Processes from the Perspective of Transportation Professionals

Vehicle miles traveled (VMT) is increasingly used as a metric for assessing the environmental effects of development projects, given its associations with greenhouse gas emissions, traffic collisions, and health outcomes. In 2013, California Senate Bill 743 mandated the replacement of the level of service (LOS) with VMT for transportation effect analysis under the California Environmental Quality Act. This study examines how transportation professionals are adapting to the implementation of VMT-based analysis, and particularly the development of off-site VMT mitigation strategies. Using a two-phased qualitative interview process, first in 2021 ( n = 19) and again in 2024 ( n = 24), this study explores evolving perceptions, challenges, and strategies related to VMT tools, legal defensibility, and equitable implementation. The findings reveal persistent uncertainty around modeling and evaluation, legal risk, and the administrative complexity of equitably distributing off-site mitigation. While grounded in California’s regulatory context, the insights offer broader relevance for jurisdictions pursuing climate-aligned transportation planning. This study calls for the development of an integrated approach to VMT modeling and evaluation, and a nuanced, multifactor understanding of the context in which new developments are being proposed when implementing off-site mitigation measures.