My new car has automatic emergency braking. How reliable is this feature? Are there speeds or situations when it won’t work? – Trina, Calgary
While systems that are designed to hit the brakes if something – or someone – is in your car’s path are getting better, don’t count on them to keep you safe, full stop, a researcher said.
“No, you should not trust these systems – they’re not perfect,” said Greg Brannon, director of automotive engineering research for the Florida-based American Automobile Association (AAA). “You should drive the vehicle like the system is not there.”
Automatic emergency braking (AEB) uses sensors and cameras to detect objects in the path of your car. If you don’t stop, it is designed to flash a warning and then apply the brakes automatically. But the systems are not foolproof.
In recent AAA tests comparing AEB systems in 2024 cars to older models, the newer systems were nearly twice as likely to avoid a collision at speeds of up to about 55 kilometres an hour. The tests were conducted in the United States, in miles an hour, but we’ll convert to metric throughout for simplicity.
Brannon’s team compared a 2018 Subaru Outback, a 2018 Nissan Rogue and a 2017 Jeep Grand Cherokee against each car’s 2024 version.
“We wanted to find out: Are the newer systems better than the older ones?” Brannon said. “And the answer to that is decisively yes.”
Better at lower speeds
In tests on a closed course, AEB on all three 2024 models prevented a collision with an inflatable test car (which wasn’t moving) 100 per cent of the time at speeds of up to 55 kilometres an hour.
But AEB in the older cars avoided a collision just 73 per cent of the time, on average.
So why are the 2024 systems so much better at detecting hazards in time to stop? It’s likely because they’re smarter, Brannon said.
“The automakers have learned a lot in terms of how to calibrate the systems,” Brannon said. “The sensors may or may not have changed ... but the key is the algorithm that is behind the sensors.”
But when the 2024 cars were tested at higher speeds, only two of them (the Rogue and the Outback) avoided a crash at just over 70 kilometres an hour.
While the 2024 Cherokee crashed in every trial at that speed, it had slowed down to a crawl, which would lessen the severity of a collision, Brannon said.
In tests at about 90 kilometres an hour, none of the AEB systems prevented a crash with the target car.
“System effectiveness dropped off as the speeds increased … and that’s not terribly surprising,” Brannon said. “There’s less time to interpret the surroundings and for the systems to try to understand whether or not they should or shouldn’t brake.”
All AEB systems need to get better at stopping at higher speeds because that’s when “more fatalities and injuries happen,” Brannon said.
Previous research has shown that AEB systems also don’t prevent crashes at intersections where vehicles are coming from the side – for example, if a car is turning left into your path, Brannon said.
They also don’t work as well at night.
“It’s been a few years since we’ve tested nighttime conditions, but generally they don’t work as well on those scenarios,” Brannon said. “There are a lot of advancements that have to come in the next few years.”
Another worry is winter weather. For instance, in Transport Canada’s winter tests of front AEB systems, three of the five vehicles tested didn’t give a collision warning when their sensors were covered in ice.
Also, systems vary widely in their ability to detect and stop for pedestrians – right now, not all AEB systems can detect pedestrians, Brannon said.
Need a brake?
The U.S. National Highway Traffic Safety Administration (NHTSA) will require all new cars sold there to have standard front AEB with pedestrian detection by September 2029.
By then, new cars travelling at up to 100 kilometres an hour will have to be able to stop and avoid crashes with vehicles in front of them and must be able to detect pedestrians in both daylight and darkness.
“It raises some of the speeds that the systems have to be effective at,” Brannon said. “It also addresses some of the pedestrian safety issues, which is one of the bigger challenges that we have as pedestrian deaths continue to escalate.”
Under the new rules, drivers won’t be able to turn the systems off – although even now, most cars don’t allow that, Brannon said.
“That’s a real benefit because if they can turn [a driver-assist system] off, people will often do that,” Brannon said.
The NHTSA rules don’t mandate rear AEB, which is supposed to stop the car if it detects a vehicle or pedestrian while backing up.
The U.S.-based Insurance Institute for Highway Safety (IIHS) welcomed the new safety requirements when they were announced earlier this year – but said it hoped automakers would voluntarily meet them sooner than 2029.
Canadian safety standards usually match U.S. ones – a rare exception is front daytime running lights, which are required on all new cars here but not in the United States.
But Transport Canada said it is still deciding whether to mandate AEB and whether it will follow the U.S. regulations.
Even before the NHTSA regulations, 20 automakers had pledged to include front AEB as standard equipment on most new cars in the United States. Because of that, most new cars in Canada, including entry-level cars like the Mitsubishi Mirage and Hyundai Venue, also have standard AEB.
Of all the accident-avoidance tech on cars now, AEB has been shown to prevent the most crashes, the IIHS said. When comparing collision rates for cars with AEB to cars without it, front AEB has been found to cut front-to-rear crashes by half – although the systems weren’t as good at preventing crashes with large trucks and motorcycles as they were with cars.
For comparison, blind-spot warnings reduced lane-change crashes by 14 per cent.
“There are other safety systems out there that probably will be mandated, but [AEB] is a really good one to start with because it has a great potential to reduce crashes and injuries,” Brannon said. “The crash data shows that it can reduce rear-end collisions by 50 per cent – and that’s amazing.”
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