Measuring, Analyzing and Identifying Small-Area VMT Reduction

Handy, Susan; Lee, Amy; Cooper, Ashley; Pourrahmani, Elham; Fukushige, Tatsuya; McGinnis, Claire · 2023 · ROSA P / National Center for Sustainable Transportation (NCST) (UTC)

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Summary

This study investigates whether changes to the built environment in specific urban areas are associated with reductions in vehicle miles traveled (VMT). Motivated by California’s Senate Bill 375, which mandates regional strategies to reduce greenhouse gas emissions through VMT reduction, the research addresses a gap in the literature: while cross-sectional studies link dense, mixed-use environments to lower driving, few longitudinal studies examine how travel behavior changes following specific built environment interventions. The primary research question asks if documented changes in land use and transportation infrastructure in selected communities correlate with decreased driving and increased active travel. The researchers conducted a retrospective case study analysis of three California cities: Sacramento, Fresno, and Santa Monica. These areas were selected because they experienced notable changes in transportation systems and land development patterns between 2000 and 2019. The methodology involved two phases. First, the team identified changes to the built environment, including public policies, infrastructure investments (such as transit, bike, and pedestrian facilities), and private development projects. Second, they analyzed travel behavior changes using available data sources, including the American Community Survey, the National Household Travel Survey, the California Household Travel Survey, and local regional surveys. To assess impact, the study compared VMT and mode share estimates in the case study areas against larger comparison areas (the broader city or county) over time, looking for widening gaps that would suggest the interventions influenced travel patterns. The findings indicate that all three cities successfully implemented significant built environment changes intended to reduce car dependence. Santa Monica experienced the most substantial changes during the 2010s, followed by Sacramento, while Fresno saw more limited changes due to a less vibrant real estate market. Analysis of travel data suggested that residents in the case study areas generally drove less and engaged in more walking and bicycling than those in the broader comparison areas. In Santa Monica, the gap in auto mode share widened, with driving decreasing in the case study area while increasing in the comparison area. In Sacramento and Fresno, estimated VMT for residents was lower in the case study areas, though the gaps did not always widen as expected. However, the authors emphasize that these results are highly uncertain and inconclusive due to small sample sizes in the travel surveys. The study concludes that while the evidence is not definitive, it supports the hypothesis that built environment changes can influence travel patterns. The lack of stronger evidence across all cases may reflect the slow pace of both physical development and behavioral change, with some interventions occurring too recently to be captured in the data. The authors argue that to robustly evaluate the impact of such policies, better longitudinal data on travel patterns must be collected before and after changes occur. They recommend that state agencies facilitate this by preserving data sources over time and requiring before-and-after evaluations for state-funded projects.

Key finding

Significant built environment changes in Sacramento, Fresno, and Santa Monica were associated with suggestive but statistically inconclusive reductions in vehicle miles traveled and increases in active transportation modes, largely due to high uncertainty in available travel data.

Methodology

field_study

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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• exposure measurement