The Environmental Protection Agency on Wednesday announced its proposals to slash pollution from just about every vehicle on the road. EPA administrator Michael Regan called the new rules “the strongest ever federal pollution standards for cars and trucks.”

But right now, it’s just a proposal, and as past attempts to clean up cars have shown, a lot can change in final regulations, if they get implemented at all.

The suite of proposals restricts pollution coming out of tailpipes, not just on cars and pickups, but also on heavy-duty vehicles, including semi trucks, buses, tractors, cherry pickers, and delivery vans. The rules would avert close to 10 billion metric tons of carbon dioxide emissions by the middle of the century, equivalent to double the total US emissions in 2022, while cutting dangerous air pollutants like nitrogen oxides in the meantime. They would drop a cinder block on the accelerator away from gasoline and diesel power and toward electric vehicles.

In the US, transportation is the largest source of greenhouse gases that are warming the planet, accounting for about 27 percent of total US emissions. Within transportation, light-duty vehicles contribute 57 percent of carbon dioxide pollution, while medium- and heavy-duty vehicles make up 26 percent. So cutting emissions from sedans, SUVs, and school buses is essential to meeting US climate change targets. The Biden administration set a goal to cut overall emissions at least 50 percent relative to 2005 by 2030.

“It is well within our grasp,” Regan told reporters at a press briefing. “Make no mistake about it.”

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Regan acknowledged that the proposal is the start of a process that will take input from the auto industry, labor organizations, and environmental groups. Republican-led states like Texas are already suing the EPA to block its existing climate change regulations for vehicles and will likely challenge the new ones. And Republican judges on federal courts, including the Supreme Court, have shown increasing hostility to environmental regulations. So the final vehicle rules could get watered down, if not stalled entirely.

Meanwhile, states like California, New York, Maryland, and Massachusetts — some of the largest car-buying markets in the country — are moving ahead with their own bans on fossil fuel-powered vehicles. Several carmakers, including General Motors, say they are betting on an all-electric future for their fleets.

Although the EPA can spur manufacturers to make more electric cars, the bigger challenge is getting people to buy them. EVs are still generally more expensive than their gasoline equivalents, and with interest rates rising, it’s getting more costly to borrow money to buy a car. A poll released Tuesday from the Associated Press and the University of Chicago found that 41 percent of Americans were at least somewhat likely to make their next car electric, but said high price tags remain the main barrier. Current EV owners are also running into growing pains with charging infrastructure as they test the legs of their cars.

To further complicate matters, EPA car pollution rules still have loopholes that favor larger, less efficient cars like SUVs and crossovers. The growing size of vehicles is undermining efficiency gains in both electric and fossil fuel-powered motors.

Some environmentalists and economists argue that to truly limit climate change, it’s not enough to switch to electric cars; we have to reduce the need for cars altogether. That will require more investment in public transportation and a broader rethinking of how cities are designed. The EPA’s new regulations could accelerate decarbonization efforts, but they must be part of a broader lineup of tactics to reach the net-zero emissions destination.

What the EPA’s new car pollution rules actually do

The EPA says its vehicle pollution regulations are technology-neutral, and the benchmarks are averaged over an automaker’s fleet of offerings rather than on individual models. The idea is that it gives carmakers the flexibility to try out a suite of approaches and encourages them to target their most popular offerings for emissions cuts rather than making a token clean car that no one buys.

The new tailpipe regulations are so stringent, however, that electrification is effectively the only way to meet the targets as they ramp up over time. By 2032, around two-thirds of new passenger cars sold will have to produce zero emissions, which means they’ll largely be battery- and fuel cell-powered electric vehicles.

“Our analysis indicates that one pathway the industry could take is to meet the standards with nearly 70 percent electric vehicles by 2032 for light-duty vehicles, and about 40 percent for medium-duty vehicles,” an EPA spokesperson told Vox in an email. “Medium-duty” refers to vehicles that weigh between 8,501 and 14,000 pounds.

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That would be a huge boost for electric cars, which comprised just 5.8 percent of new car and light truck sales in 2022. While electric vehicles tend to cost more — the average new car last year cost around $48,000, while the average new electric car cost $66,000 — the proposed regulations would save the average car buyer $12,000 over the life of the vehicle, according to the EPA, largely through averted fuel costs and lower maintenance.

Across the economy, the regulations would avoid $12 billion in oil imports. The EPA is also leaning on the health benefits of the regulations. By avoiding combustion byproducts like particulates and sulfur oxides, EVs are already having a positive impact on air quality in some parts of the country. Regan said that reducing the harms of this pollution, like heart attacks and asthma attacks, would have between $850 billion and $1.6 trillion in economic benefits over the course of the new rules.

But rumbling internal combustion engines aren’t driving off into the sunset just yet.

Because the regulations are “technology neutral,” they don’t explicitly outlaw fossil fuels, and the EPA acknowledged that such vehicles will still be on the market. An EPA spokesperson said the agency projects that “advanced gasoline vehicles will continue to be a part of manufacturers’ product plans.” In addition, the regulations affect sales of new vehicles, not existing ones. The average car stays on the road for more than 11 years, so some of the dirtiest vehicles on the road today will still be rolling in 2032 and beyond.

The EPA also noted that its proposed emissions rules are not being issued in a vacuum, but are meant to integrate with a host of other climate change policies across the government. The Bipartisan Infrastructure Law includes close to $25 billion for tactics like building out a network of EV chargers and buying zero-emissions school buses, while the Inflation Reduction Act contains around $6 billion in loans and grants to build and deploy more clean vehicles, along with tax credits for buyers, according to the Biden administration. The White House is aiming to nearly triple the current number of public EV chargers to 500,000 by 2030 alongside investments in building a supply chain for batteries and training a workforce for cleaner transportation. The federal government is also using its purchasing power to create a larger market for EVs, including electrifying its largest fleet: postal trucks.

Cleaner cars and trucks still have a bumpy road ahead

Of course, all this hinges on whether the EPA can implement its proposal as is, and that’s not a guarantee. Some carmakers may push back and argue the targets are unfeasible, while courts could become a roadblock. And the next election could drive everything off course.

Car emissions rules at the EPA already took a handbrake turn from Obama, who sought to make them stronger than ever, to Trump, who tried to undo them entirely. Biden’s EPA is making another U-turn, but if he doesn’t hold on to the Oval Office, the next president could throw the regulations in reverse once more.

The current economy, with worries about inflation and high interest rates, is also adding potholes for people and businesses driving to buy cleaner vehicles.

And the Americans that are buying cars and trucks like ’em big. SUVs and crossovers now account for half of cars sold in the US. The EPA’s Automotive Trends Report last year said that the growing size of vehicles has “offset some of the fleetwide benefits that otherwise would have been achieved from the improvements within each vehicle type.” That includes the environmental benefits of electric cars.

Vehicles like SUVs have larger profit margins for carmakers compared to sedans, but the EPA’s regulations also end up giving these bigger, less efficient vehicles more favorable treatment. Crossovers — larger vehicles built on car platforms — are often classified as light-duty trucks rather than cars and thus held to lower fuel efficiency and pollution standards.

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The distinction can get blurry for the EPA, however. “For instance, one of the best-selling [crossover] models is the Honda CR-V. The two-wheel drive CR-V qualifies as a passenger car, and the all-wheel drive CR-V qualifies as a light truck,” noted the Energy Information Administration.

Cutting greenhouse gas emissions from transportation also requires looking beyond cars and trucks, toward creating more viable alternatives like rail, bikes, and even walking in some cases. And roads aren’t the only source of heat-trapping gases: The bigger technical challenge will be decarbonizing shipping and aviation, finding a way to power the largest vehicles without burning fossil fuels.

So the EPA’s new vehicle emissions rules have set a new finish line, and some in the industry are already racing toward it. But it will take a steady hand at the wheel to make sure everyone crosses the line.