Mayors are fighting the EPA’s emissions rollback. What cities need are fewer cars.

A group of over 400 mayors formed to protest the U.S.’s exit from the Paris climate accord joined a growing chorus of politicians and environmentalists in denouncing the Trump administration’s plan to revoke California’s vehicle emission waiver—a plan to erase the country’s ambitious fuel-efficiency goals and severely hamper the fight against climate change.

Any leader that wants clean air and healthy communities should clearly oppose this move. But true climate mayors should be working harder to promote policies in their cities that would make it easier for drivers to stay out of their cars in the first place—and most of these mayors aren’t doing it.

Almost half of the country’s population and about a third of the vehicles on the road are already subject to stricter vehicle emissions standards than current U.S. policy requires. For almost five decades, California has set higher fuel-efficiency standards than the federal government under the Clean Air Act as part of an effort to reduce emissions, and 12 other states have since adopted its standards.

In cooperation with California, the Obama administration set fuel-efficiency goals intended to bring federal standards up to the state’s standards. The auto industry agreed to produce fleets with an average fuel efficiency of 54.5 miles per gallon by 2025 (which at the time was on target to be one of the most aggressive fuel economy goals in the world—although many countries have since proposed outright bans on internal combustion vehicles, and many presidential candidates want only electric vehicles to be sold in the U.S. by 2030).

The Trump administration's goal is for its federal fuel-efficiency standards to no longer have an exception for California. But after the EPA first announced the rollback, several automakers said they would stick to California’s standards—not a new one presented by the EPA. Ford, Honda, BMW and Volkswagen confirmed they will stick to the deal, which was brokered by California’s air resources board chair Mary Nichols.

“Automakers, environmentalists, local communities, our state, and our city are all on the same page,” said Los Angeles Mayor Eric Garcetti in a statement. “No matter what happens in Washington, we are committed to stopping this reckless and unlawful approach, and using our purchasing power to invest in zero emissions technology, energize a dynamic and innovative car market, and protect the well-being of our families and generations ahead.”

But data proves that fuel-efficiency regulations have not been enough to curb emissions in California. Even though California managed to reduce its overall emissions to 1990 levels, reaching its target for 2020 early, the state’s transportation emissions went up by 2 percent. What’s more, passenger vehicles specifically now make up the state’s largest portion of greenhouse gas emissions.

Which is why aiming for fuel-efficiency standards in 2050 doesn't address the real problem—right now, Americans are driving their own cars more than ever.

Transportation is the largest, fastest-growing source of greenhouse gas emissions in the U.S. This can be easily witnessed in a city like Los Angeles, which is adding cars at a rate four times faster than it did during the 1990s. Or in Houston, which has the highest per-capita greenhouse gas emissions of all U.S. cities and where transportation is responsible for 48 percent of the city’s total emissions.

Across the country, the number of vehicle-miles traveled, or VMT, keeps going up. And it will continue to go up until leaders of cities—many of whom have set stringent climate goals—step forward to propose an even more ambitious and impactful goal: to greatly reduce the number of miles driven by private cars within their cities.

The climate mayors might “vow to continue moving forward on transportation policies that help reduce the impact of climate pollution.” But as other cities outside the U.S. have shown, most effective policies are simple changes to the way cities fundamentally work—making walking and biking the easiest way to get around, building affordable housing near transit, prioritizing infrastructure like dedicated bus lanes that move the most people most efficiently.

One-third of all vehicular trips in this country are two miles or less. A whopping 85.5 percent of all miles traveled in cities is by private car. The fastest way to reduce emissions is to help Americans drive less.

If city leaders focused on shifting a portion of those trips away from vehicles, the fight against arcane fuel-efficiency standards would be less critical. The ultimate affront to the Trump administration’s embrace of oil companies—companies that have led decades-long misinformation campaigns to stifle climate action and defeat public transportation investments—would be to build cities that are less reliant on gas-powered vehicles.

It is admirable that these 430 mayors are stepping forward, again and again, to stand up to the Trump administration’s destructive climate policy. But instead of a pledge to remain “committed to leading on climate action,” climate mayors need to pledge to the residents of their cities that they will help them achieve their daily goals without the environmental and economic burden of owning, maintaining, and putting gasoline into a car—no matter how many miles it gets to the gallon.