Associations between Vehicle Miles Traveled and Ambient Air Pollution at Regulatory Monitoring Sites: A Natural Experiment using the COVID-19 Shutdown

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BACKGROUND AND AIM: Transportation planners calculate vehicle miles traveled (VMT) to forecast roadway usage and inform policy decisions. However, the relationship between VMT and ambient air pollution is not fully understood. In this analysis, we use proprietary smartphone sensing data with VMT calculations to examine the impact of VMT on ambient air pollution during the decline in vehicle usage from the COVID-19 shutdown. We aim to determine how VMT change contributes to change in NO2, O3, and PM2.5 concentrations and at what spatial scale these changes occur. METHODS: We obtained access to a daily national database with VMT calculations for January to July 2020, which corresponds to various stay at home orders that limited travel needs. We linked VMT measures at different buffer distances (100, 300, 500, 1000, 2000 and 3000m) to ambient air pollution monitor from the Environmental Protection Agency (EPA). We implement multi-level linear regression models to examine how NO2, O3, and PM2.5 changed with VMT reductions in different distance buffers around monitoring locations. RESULTS:Preliminary results show consistent associations between VMT and O3 and NO2 at varying buffer distances, but these associations are less consistent for PM2.5. For O3, we observe a 0.18 ppb (95% CI: -0.21, -0.15) reduction per 1,000 VMT at the 100m buffer but this reduction increases to 0.47 ppb (95% CI: 0.52, 0.43) at the 3,000m buffer. For NO2, we observe a 2.21 ppb (95% CI: 2.13, 2.30) increase per 1,000 VMT at the 100m buffer and results are similar out to the 3,000m buffer. When we split out VMT by road type, we find that models for VMT from expressways yield smaller magnitudes of association than the models for VMT from non-expressways. CONCLUSIONS:These results will be used to inform future analyses on how congestion reduction projects impact local air pollution and population health. KEYWORDS: Traffic-related, Policy research, Exposure assessment-air pollution, Oxides of nitrogen, Particle components, Ozone