Innovative Brake and Tire Emissions Research

Due to the widespread use of particulate matter filters in light- and heavy-duty vehicles, PM emissions from vehicle tailpipes have markedly declined. As a result, brake and tire wear are now projected to become the primary source of vehicular PM emissions. The California Air Resources Board wanted to measure and quantify brake and tire PM emissions in order to inform air quality planning and policy in the state. CARB contracted with ERG to conduct two brake wear emissions research projects and support additional research to measure on-road brake and tire wear emissions.

ERG worked in partnership with the automotive testing firm, LINK Engineering, to conduct both brake wear studies. The first study focused on cars and light-duty trucks. The ERG team analyzed instrumented vehicle data to develop a test cycle that represented braking behavior in California. They also estimated brake temperatures on this cycle based on track testing. Next, they used a LINK brake dynamometer to test brake emissions over the test cycle on six vehicle models and three different brake pad types. They then analyzed the raw emissions data in conjunction with market share data to estimate brake PM emission factors for passenger cars, light trucks, and hybrids. The second study, which was supported by the California Department of Transportation, focused on heavy-duty trucks and an electric light-duty vehicle. For this study, the ERG team measured brake PM emissions on a variety of heavy-duty truck classes and brake configurations over several vocational duty cycles and loadings. It was the most comprehensive heavy-duty brake wear emissions measurement program ever conducted. CARB used the results of both studies to update vehicle emissions factors for brake wear in the EMFAC2021 modeI. In an ongoing project through 2026, ERG has been leading a research consortium for a CARB project to measure brake and tire wear emissions on a vehicle while driving on the road.