The pressure is on for California to meet its clean-vehicle goals. In less than two years, 35% of vehicles sold must have zero tailpipe emissions. And by 2035, all light-duty vehicles sold must be zero-emissions.

Automakers have ramped up their production of battery electric and plug-in hybrid vehicles to meet this mandate, and so far, sales seem to be on track. But many questions remain on how to achieve this wholesale revamping of transportation. Experts at UC Davis are researching how to overcome the remaining road bumps to eliminating tailpipe emissions. Here, they answer some common questions on California's zero-emissions mandates.

Where did the California mandate come from?

While the zero-emissions target may have felt sudden to some when Gov. Gavin Newsom announced it in an executive order in 2020, it's really the next milestone on a road that state officials have been pursuing since the 1990s.

California first began to introduce regulation in the early 1990s, explained Alan Jenn, an assistant professor in the UC Davis Department of Civil and Environmental Engineering and researcher at the UC Davis Institute of Transportation Studies. At the time, unhealthy air plagued regions such as the Los Angeles metropolitan area and inland valleys—frequently, cities failed to meet federal and state thresholds for pollutants. So, officials started setting targets for automakers to offer zero-emissions vehicles among their fleets. But, as automakers stalled in the rollout of clean cars, regulations were delayed.

Finally, when in the 2000s automakers began rolling out viable hybrid and electric vehicles, the state air resources board started putting formal targets in place. The governor's executive order was really the next step to ensure continued progress along this route, said Jenn. In 2022, the air resources board formalized the executive order, making it official that all light-duty vehicles—including passenger cars, trucks and SUVs—sold in the state must be zero-emissions by 2035.

Are we making enough progress to achieve the mandate?

Aside from a couple of flat years of sales between 2018 and 2020, sales of electric vehicles in California have been rising since 2011. Today, one in four new cars sold in the state is an EV, said Dahlia Garas, program director at UC Davis' Electric Vehicle Research Center.

As batteries become cheaper, ranges increase and competition increases between automakers, electric vehicles are growing more affordable and attractive to drivers. "We're making reasonably good progress," said Garas. "I think our market is actually really strong."

Still, recent news headlines have called attention to the fact that sales in 2023 slowed down. To be clear, more EVs still sold in 2023 than 2022—but the rate of increase dipped. During the 2019 dip, there were also worries that EVs had reached a market saturation point, but the slowdown turned out to be temporary, said Jenn. He said he remains optimistic. "It's hard to make those conclusions from these small blips in the data," he said.

Will the electric grid be able to support that many EVs?

To achieve the zero-emissions vehicle mandate, California will need about 15 times as many electric cars on the road as today. From an energy supply standpoint, state officials believe the state will have a capacity to keep all these cars charged, with planned expansion of wind and solar power.

That said, the rollout of electric vehicles may strain the grid, especially if they are all charging at the same time, such as in the evening when people get home from work. In addition to needing a lot of electricity available at those times, that demand could exceed the capacity of local infrastructure, including neighborhood transformers. Utilities will need to upgrade much of this local equipment.

Luckily, encouraging people to spread out their charging times could help with the above issues, said Jenn. For instance, if more people have the option to charge during the day—for example, using a charger at their workplace—that would shift demand away from peak evening hours. Incentivizing daytime charging also has the added benefit of drawing power when the sun is out, supplying vehicles with clean and plentiful solar.