The world is full of feel-bad news. Here’s something to feel good about: Automatic emergency braking is one of the great car safety-tech success stories.

Auto-braking systems, called AEB for short, use sensors including cameras, radar, and lidar to sense when a crash is about to happen and warn drivers—then automatically apply the brakes if drivers don’t respond. It’s a handy thing to have in those vital few moments before your car careens into the back of another. One industry group estimates that US automakers’ move to install AEB on most cars—something they did voluntarily, in cooperation with road safety advocates—will prevent 42,000 crashes and 20,000 injuries by 2025.

A new report from AAA finds these emergency braking systems are getting even better—and challenges automakers to perfect them at even higher speeds.

AAA researchers tested three model year 2018 and 2017 vehicles versus three model year 2024 vehicles, and found the AEB systems in the newer cars were twice as likely as the old systems to avoid collisions at speeds up to 35 miles per hour. In fact, the new systems avoided all of the tested collisions at speeds between 12 and 35 mph. The majority of the newer cars avoided hitting a non-moving target at 45 mph, too.

The systems “are headed the right way,” says Greg Brannon, the director of automotive research at AAA.

Now new regulations will require AEB systems to get even more intelligent. Earlier this year, the US National Highway Traffic Safety Administration, which crafts the country’s road safety rules, announced that by 2029, it will require all cars to be able to stop and avoid contact with any vehicle in front of them at even faster speeds: 62 mph. The Feds will also require automakers to build AEB systems that can detect pedestrians in the daytime and at night. And automakers will have to build tech that applies brakes automatically at speeds up to 45 mph when it senses an imminent collision with a person, and 90 mph when it senses one with a car.

The rule will require automakers to build systems that can operate at highway speeds. As a result, it should do more good; according to the NHTSA, if manufacturers deploy auto-braking systems that work at higher speeds, it would save at least 360 lives each year and prevent 24,000 injuries.

But no story can be all good news. Auto industry officials argue that meeting that 2029 target will be really very hard. “That’s practically impossible with available technology,” John Bozzella, the president and CEO of the auto industry lobbying group the Alliance for Automotive Innovation, wrote earlier this year in a letter to Congress. The government estimated that installing more advanced AEB systems on its cars would cost an additional $350 per vehicle. The auto lobbying group estimates prices could range up to $4,200 per car instead, and it has filed a petition to request changes to the final federal rules.

In response to WIRED’s questions, a spokesperson for NHTSA said that more advanced AEB systems “will significantly reduce injury or property damage and the associated costs from these crashes.” The spokesperson said the agency “is working expeditiously” to reply to the group’s petition.

Auto safety experts say that if automakers (and the suppliers who build their technology) pull off more advanced automatic emergency braking, they’ll have to walk a tightrope: developing tech that avoids crashes without ballooning costs. They’ll also have to avoid false positives or “phantom braking,” which incorrectly identify nonhazards as hazards and throw on the brakes for no apparent reason. These can frustrate and annoy drivers—and at higher speeds, give them serious cases of whiplash.

“That is a really big concern: That as you increase the number of situations in which the system has to operate, you have more of these false warnings,” says David Kidd, a senior research scientist at the Insurance Institute for Highway Safety (IIHS), an insurance-industry-funded scientific and educational organization.

Otherwise, drivers will get mad. “The mainstream manufacturers have to be a little careful because they don’t want to create customer dissatisfaction by making the system too twitchy,” says Brannon, at AAA. Tesla drivers, for example, have proven very tolerant of “beta testing” and quirks. Your average driver, maybe less so.

Based on its own research, IIHS has pushed automakers to install AEB systems able to operate at faster speeds on their cars. Kidd says IIHS research suggests there have been no systemic, industry-wide issues with safety and automatic emergency braking. Fewer and fewer drivers seem to be turning off their AEB systems out of annoyance. (The new rules make it so drivers can’t turn them off.) But US regulators have investigated a handful of automakers, including General Motors and Honda, for automatic emergency braking issues that have reportedly injured more than 100 people, though automakers have reportedly fixed the issue.

New Complexities

Getting cars to fast break at even higher speeds will require a series of tech advances, experts say. AEB works by bringing in data from sensors. That information is then turned over to automakers’ custom-tuned classification systems, which are trained to recognize certain situations and road users—that’s a stopped car in the middle of the road up ahead or there’s a person walking across the road up there—and intervene.

So to get AEB to work in higher-speed situations, the tech will have to “see” further down the road. Most of today’s new cars come loaded up with sensors, including cameras and radar, which can collect vital data. But the auto industry trade group argues that the Feds have underestimated the amount of new hardware—including, possibly, more expensive lidar units—that will have to be added to cars.

Brake-makers will have to tinker with components to allow quicker stops, which will require the pressurized fluid that moves through a brake’s hydraulic lines to go even faster. Allowing cars to detect hazards at further distances could require different types of hardware, including sometimes-expensive sensors. “Some vehicles might just need a software update, and some might not have the right sensor suite,” says Bhavana Chakraborty, an engineering director at Bosch, an automotive supplier that builds safety systems. Those without the right hardware will need updates “across the board,” she says, to get to the levels of safety demanded by the federal government.

Bosch and other suppliers advise automakers how to use the systems they build, but manufacturers are ultimately in charge of the other AEB secret sauce: algorithms. Each automaker “tunes” its safety system, using its own calculations to determine how and when its vehicles will automatically avoid collisions.

What’s Next

Even the US Feds’ 2029 rules don’t fulfill all road safety advocates’ dreams. The regulations don’t require safety systems to recognize bicyclists, though some automakers are already building that into theirs voluntarily. And unlike European vehicles, US AEB systems won’t undergo tests that determine how well they work when they’re turning. The European New Car Assessment Program started testing AEB for turning effectiveness last year, and has for several years required automakers to build systems that totally avoid crashes at higher speeds. Some automakers are already building systems that pass these tests, says Kidd, the IIHS scientist—a good sign that they’ll be able to pull it off on US roads too.

“I don’t think there’s any doubt that these will make the roads safer,” Kidd says. A good news story after all.