President Donald Trump made headlines recently by signing resolutions that bar individual states from setting their own tailpipe emissions standards or mandating the sale of certain vehicles, such as EVs. The truth is, he just reversed a waiver that allowed California and other states to set stricter guidelines than the federal government. Before this loophole, states had alternative ways of influencing emissions.

Mandating the cars available on dealership lots

While the federal government’s EPA may pass emissions rules, dealerships are still local businesses. And thus, states have much more control over dealerships. One way California first pushed for EV adoption was by requiring automakers to sell a certain percentage of zero-emissions vehicles. This is why the first generation of mass-produced EVs came out over a decade ago—and many were California-only.

Other states have pioneered an interesting twist on the California guidelines. Instead of telling dealerships what they can sell, they tell dealerships what percentage of their inventory needs to be zero-emissions vehicles. The logic is that buyers are still free to special order anything they want. But if the lot always has hybrids and EVs, folks will buy them. And dealerships will be eager to sell them.

Stricter emissions testing

The federal government will now be setting emissions standards across the country. But states will still be enforcing these standards for used cars. And many states are a bit loose in their enforcement.

Some states only check cars every few years. Others give cars a pass for the first 10—or even 15—years they are on the road. In Massachusetts, old cars don’t have to pass an emissions test. They just can’t be producing “visible smoke.” Strictly enforcing the emissions laws that exist is another way a state could influence its air quality.

Should California decide their own emissions standards?

You might think, because we all share the air, its quality is a federal issue. But as California struggled with unlivable smog in L.A., improving its regional air quality became a matter of life and death. I’ve written before that it’s foolish to design diesel truck engines destined for North Dakota to meet Los Angeles smog standards. The resulting engines cost more, get worse mpg, and don’t last as long. And this design does nothing to limit greenhouse gases.

This is one reason the federal government originally passed a waiver, allowing states—and even counties—to set stricter emissions guidelines. Seventeen states agreed, voting in unique emissions laws.

When President Trump reversed this waiver he said, “We officially rescued the U.S. auto industry from destruction by terminating the California electric vehicle mandate once and for all.”

California Governor Gavin Newsom responded by saying he’d sue to “stop this latest illegal action by a President who is a wholly owned subsidiary of big polluters.”