When a California pollution regulator voted last month to approve a rule banning new gas-powered car sales in the state by 2035, its officials were hailed as climate heroes. With good reason too: The move will reduce emissions by nearly 400 million metric tons between 2026 and 2040, the state calculates, preventing an estimated 1,300 deaths from heart- and lung-related ailments. The ban is the first such move in the US and among the most aggressive climate regulations in the world. It underscores the Golden State’s position as a powerful proving ground for environmental policy. What’s more, an auto industry already excited about electrification seems to have taken the whole thing in stride. Experts say the goal should be well within reach, too; after all, more than 16 percent of new cars sold in California this year were zero-emission.

That’s the good news. Here’s the bad news: California still has lots of work to do, because electrifying cars alone won’t be enough to stave off the worst of climate change. In a draft report released this summer, the state’s Air Resources Board turned to another policy needed alongside banning gas cars: reducing the number of miles that Californians drive every year. “Even with improvements in clean vehicle technology and fuels,” the agency wrote, “it is still necessary to reduce driving to meet state climate and air quality commitments.”

The state has committed to driving less because, for one thing, it’s going to take a while for all California cars to become zero-emission. Despite new purchases and old cars getting scrapped, the average age of cars on US roads keeps increasing—today, the average is more than 12 years. Existing gas-powered cars will stick around long after they’re banned from new car lots. Plus, there are plenty of emissions associated with cars and driving that don’t come out of a tailpipe, including manufacturing the vehicle in the first place, and the stuff that cars drive on. Building and maintaining just one lane-mile of highway creates some 3,500 tons of carbon emissions, according to one analysis.

Despite its target, California has not so far managed to significantly reduce driving. In 2019, the last year of strong data, Californians were driving and riding in cars more, as measured by annual vehicle miles traveled per person, than they were 14 years earlier. They were carpooling, biking, and walking to work less. And fewer people were taking the bus or train, a pattern that has worsened since the beginning of the pandemic. By 2035, the state aims to reduce the miles traveled by vehicle by the average Californian by 19 percent, compared to 2005. But preliminary data suggests that by 2019, that number had moved in the opposite direction. (In public comments, a number of regional agencies have argued that they have reduced driving miles more than the Air Resources Board calculates in its draft report.)

The rest of the US needs to drive less too. An analysis from the Rocky Mountain Institute, a sustainability research organization, estimates that by 2030 the US must reduce the miles it travels by car by 20 percent to limit global warming to 1.5 degrees Celsius. Beyond that, the experience of living on Earth is likely to get much worse.

Unfortunately, the inertia from a century of US urban planning has made it very difficult to live in many places without driving. “What we’re trying to do is to get people to drive less, but for a lot of people, that’s just not very possible,” says Susan Handy, a professor of environmental science and policy at UC Davis. “What we need to do is rebuild and adjust our communities so that it becomes just possible to drive less,” she says.