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Stop! Or your next car will for you, thanks to automatic braking

The National Highway Traffic Safety Administration (NHTSA) and the Insurance Institute for Highway Safety (IIHS) recently announced that 20 automakers have committed to making Automatic Emergency Braking (AEB) a standard feature on virtually all of their new cars by September of 2022. That news may have slipped by most of us because it’s an election year, but it’s significant. This technology matters to anyone who’s ever looked up from changing a radio station and saw that the traffic in front of them had stopped. Most of us have narrowly avoided a crash at some point – or worse, we didn’t avoid it.

The 20 automakers signing onto this agreement represent the bulk of the auto industry. The vast list includes Audi, BMW, Fiat-Chrysler, Ford, General Motors, Honda, Hyundai, Jaguar, Land Rover, Kia, Maserati, Mazda, Mercedes-Benz, Mitsubishi, Nissan, Porsche, Subaru, Tesla, Toyota, Volkswagen and Volvo. All the various sub-brands will get the technology, too, so throw in Acura, Genesis, Lexus, Infiniti, and so on. Taken together, these automakers represent about 99% of the new car market in America.

Increase the speed by just 10 MPH and the stopping distance almost doubles.

The basic idea is simple enough: If your vehicle senses that a front-end collision is imminent and you’re not using the brakes, it’s going to actuate the brakes for you to try and minimize or prevent the impact. The standard is based on two tests that NHTSA will perform on every vehicle. They will aim each car at a solid target at 12 mph and at 25 mph. To be certified, the car has to reduce speed by 10 mph on at least one of the tests, or by 5 mph on both tests. Basic math indicates that the cars can still hit the obstacles, but at a lower speed. In practice, manufacturers plan to do much better than that, stopping the car entirely in most instances.

The challenge of stopping distance

This may sound quite obvious, but stopping a moving car is a big deal. Most modern cars weigh at least 3,000 pounds, with many topping 4,000 pounds. If that much mass is moving at 25 mph, you have to zero out a lot of inertia to stop it. Using baseline calculations, the generally accepted minimum distance to stop a car moving at 25 mph on dry asphalt is about 30 feet.  That’s under perfect conditions with good tires. For most vehicles and most road surfaces, things are somewhat less than perfect. Here’s the thing – if you bump the speed up to 35 mph, perfect stopping distance is at least 58 feet. Got that? Increase the speed by just 10 mph and the stopping distance almost doubles. Accelerate to 45 mph and most cars will take at least 96 feet to stop under perfect conditions. Throw in rain, snow, or even a declining angle, and things get much worse.


When we drive, we anticipate things that we know or suspect will happen in the near future. For example, we see the stoplight coming up and it’s green, but it’s been green for a while so we are not surprised when it changes. We see traffic bunching up ahead and we get ready to slow down. Because of this, we can stop smoothly with some margin for safety. If we could not anticipate these things, every stop would require full-force panic braking with the ABS pumping and seat belts cinching up.

Because stopping distance rises quickly with speed, but human drivers almost always anticipate stops coming up, automakers have a big problem when it comes to deciding when the human driver has failed to recognize a danger. If the car takes over the brakes too soon, it will be very difficult to drive smoothly. If the car doesn’t take over the brakes, well, that’s why people crash into things. What the automakers have to do is come up with a system that will reliably slow a car down to minimize crash damage without taking too much control away from the driver.

How automatic emergency braking works

Each automaker will come up with its own implementation of the automatic braking function, but they will all use the same type of underlying technology. Each car will use some combination of radar, lasers, and forward-looking cameras to monitor the road ahead, measuring the distance to any obstacle in the vehicle’s path. That technology already exists and has been used for following distance warnings and collision alarms, as well as for adaptive cruise control that follows the speed of traffic. What automatic emergency braking does is bring the car’s braking system more completely into the program.

When an AEB-equipped car is driving, information about objects in the car’s path is combined with the car’s current speed and whether or not the driver is stepping on the brakes. The car will calculate the danger of a collision based on those factors and if a collision is likely, the car will warn the driver with a sound and perhaps a visual cue, and pre-pressurize the brake system for maximum stopping force. If the driver does not respond in time, the car will actuate the brakes on its own.

Testing this function on an AEB-equipped car is instructive. The Subaru Outback with the EyeSight feature, for example, will stop the car within inches of an obstacle. The stopping is always smooth and measured, but a stop from 10 mph ends at about the same distance from the obstacle as a stop from 20 mph. That happens because the computer can calculate exactly how much brake force to use to stop just in time for the relative speeds of the car and the obstacle. The computer actually does a better job than most drivers can manage.

Optional today – standard tomorrow

It’s worth noting that virtually all the automakers on the agreement list have automatic braking technology in production today. Beginning with audible collision warning systems, automakers have raced to get full collision avoidance to market over the last 10 years. The technology has spread through the industry quickly, but as of today it’s still optional, expensive, and often limited to higher trim levels. The important thing about this new agreement is that the automakers have committed to offer the technology as a standard feature on all their vehicles.

Automatic braking isn’t free, but if everyone has it the cost of the technology is spread out over the entire market, and every driver on the road will be safer. According to research conducted by Volvo, 75 percent of all reported collisions take place at speeds of 19 mph or less, and in 50 percent of rear-end collisions, the driver has not yet stepped on the brake when the crash occurs. Automatic braking will eliminate most of those impacts.

Research by the IIHS shows that automatic braking systems will likely reduce the number of rear-end crashes by 40 percent. In the first three years, that could add up to 28,000 crashes and 12,000 injuries that won’t happen because this technology has been installed in every new car. That makes this industry agreement something to really cheer about.