Assessment of COVID-19 impacts on VMT, on-road emissions, and air quality in California

Abstract:

In California, transportation is one of the major sources of emissions of nitrogen oxides (NOx), a significant precursor to smog and particulate matter, and is the largest contributor to greenhouse gas (GHG) emissions. In 2017, passenger vehicles and heavy-duty trucks in California were responsible for 45 % of statewide NOx and 37 % of statewide GHG emissions excluding emissions from production of fuels that power them.

Notable changes have been observed in transportation activities, during the COVID-19 pandemic. The COVID-19 shelter in place orders have given us a preview of the potential air quality and climate impacts of VMT and transportation activity reduction in California. EMission FACtor (EMFAC), which serves as the primary tool to assess emissions from on-road vehicles in California, is used as the foundational framework, coupled with vehicle activity monitoring and tracking from multiple publicly accessible data sources to quantify the post COVID-19 reduction in VMT and the associated changes in on-road emissions.

The statewide transportation activity impacts have been assessed mainly for light-duty passenger vehicles and heavy-duty trucks, and also some off-road sectors. According to Performance Measurement System (PeMS) data provided by the California Department of Transportation (Caltrans) and other private entities such as Streetlight.com, average daily VMT on California roadways have been reduced somewhere between 40-75% during the first and second weeks of April. Weigh-in-Motion (WIM) devices at truck weigh stations and records provided by telematics service providers show that truck activities have been reduced by up to 25%. The emission analysis has highlighted the disproportionately large contribution of heavy-duty trucks to the total NOx inventory, and light-duty passenger vehicles to the total GHG emissions. The preliminary results show that the reductions of vehicle VMT due to COVID-19 result in up to 64% CO₂ reduction and up to 38% NOx reductions from the on-road sector in California. The time period with maximum overall VMT reductions coincide with maximum averaged observed ambient pollution reductions recorded at air monitoring sites.