Assessing Emissions of the Least-Well Understood Vehicle with the California Air Resources Board
Max Kessler, PhD ’26 Mechanical Engineering
Graduate Fellow, California Air Resources Board (CARB)
The 35.7 million vehicles registered in Californiai cause more than just traffic; about half of the state’s current greenhouse gas emissions come from transportation and production of the fuel it consumesii. Vehicle tailpipes also produce smog and other toxic air pollutants, affecting public health and the environment. To help California meet its air quality and climate change targets, the California Air Resources Board (CARB) has developed the Advanced Clean Cars (ACC) regulation. In its second version, ACC II mandates that an increasing number of new car sales in California be zero-emission vehicles (ZEVs), reaching 100% ZEVs by 2035 (see chart below)ii.
The current rule allows 20% of new cars sold in 2035 to be plug-in hybrid electric vehicles (PHEVs), which are highly efficient gasoline-powered cars that also have an electric motor + battery. When charged, PHEVs typically offer an all-electric range of ~40 miles, perfect for daily driving, resulting in less emissions and cost savings over fuel… at least in theory. In reality, PHEV owners may not charge their car every day (meaning they haul around an unused battery) or may not drive their car as efficiently as they could (e.g., using gas on the highway—when the engine is most efficient—and using electricity in the city). Consumer Reports labels PHEVs as the least-well understood type of vehicleiii. Consequently, recent findings suggest that the actual emissions of PHEVs are worse than regulators assumeiv.
If PHEVs are to play an effective role in the transition to clean transportation and factor into CARB’s ACC II ZEV requirement, their actual emissions must be better understood. My project this summer has been to analyze data on PHEV usage and performance. In my last month, I am still assessing trends and considering policy implications.
What have I taken away from the experience? I have learned a lot about cars! — how they are made and how they are regulated. I was surprised to learn how fast-paced government work can be. In one summer, my team has made a large headway in amending the ACC II regulation to align with a recent federal ruling from U.S. EPAvi, hosted a workshop to share plans with the public, and met with car manufacturers to hear their comments (and grievances). I have never been on a team that is so lively and full of humor. It has been a huge privilege and pleasure.
This experience also reinforced my interest in public policy. I am still a researcher at heart, but I am now convinced that research is most impactful when it informs policy decisions, whether that be in developing new technology, furthering justice, improving old practices—or ideally all of the above. I now see my dream job to be a mix of research and policy. I am very grateful to CARB and the Shultz Fellowship for enabling this summer experience.
[i] https://www.dmv.ca.gov/portal/news-and-media/dmv-statistics/ (accessed 13 Aug 2024).
[ii] https://ww2.arb.ca.gov/sites/default/files/2024-06/ACCII_Amendments_FS.pdf (accessed 13 Aug 2024).
[iii] “Plug-In Hybrids Are Not What You Think They Are,” Talking Cars with Consumer Reports (Oct 2023).
[iv] “Real world usage of plug-in hybrid vehicles in the United States,” International Council on Clean Transportation (Dec 2022).
[v] https://www.veloz.org/california-new-ev-sales-continue-to-grow-and-market-share-rises-again/ (accessed 13 Aug 2024).
[vi] “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles,” United States Environmental Protection Agency (Mar 2024).
