Is Automatic Emergency Braking Dangerous?

Posted by

Automatic emergency braking is proven to stop accidents. But can it also cause them when it fails? Here’s our take having tested thousands of new vehicles.

Automatic emergency braking (AEB), forward collision mitigation and warning, and other systems that are designed to look for trouble ahead and warn you or brake for you. However, that automatic braking potential concerns some shoppers. Since the early days of this technology, any story covering the topic has earned comments from shoppers who are worried about one thing; That the system will stop their car abruptly in a situation where it will actually cause a rear-ending accident. New data shows that this concern may be valid.

Looking for a great new or used vehicle? Start your search at 

In the fall of this year, Nissan announced a NHTSA investigation and recall related to its Rogue crossover. Owners have reported that their Rogue vehicles stopped when there was no reason to do so. Accidents and injuries have been reported related to these incidents. BestRide reached out to Nissan and asked if the issue has been identified and a fix put in place.

Nissan’s representative told us, “Nissan is committed to the safety and security of our customers and their passengers. Nissan has investigated this issue extensively and, in consultation with NHTSA, launched field actions notifying affected customers of a software update that improves MY17-18 Rogue AEB/FEB system performance. Customers are invited to bring their vehicle to an authorized Nissan dealership where the update will be applied at no cost to the customer. As always, Nissan will continue to work collaboratively with NHTSA on all matters of product safety.”

Most recently, Mazda has also reported that a NHTSA investigation and likely recall will result from unwarranted emergency braking in its Mazda3. Mazda says that there have been no injuries reported to NHTSA with that model. However, a search by Consumer Reports of NHTSA data did find a reported crash with injuries related to this pending recall.

AEB and warning systems related to it use sensors to detect a situation where a vehicle may be about to crash head-on into another object. It could be another vehicle, a tree, a utility pole, a person, or anything the sensors detect ahead. Normally, vehicles equipped with the systems will first provide a warning. Usually, both audible and visual warnings. If no action is taken by the driver, or if the event happens very rapidly, many systems are able to provide braking to either prevent a crash or reduce its severity.

Related Story: New Study Of GM Vehicles Shows Auto Braking Dramatically Reduces Crash Rates

One of the first well-known auto testers to report AEB preventing a crash was Ezra Dyer. He reported that an Audi in which he was the driver auto-braked averting a serious crash. Dyer is an automotive content provider and editor at Car and Driver and Popular Mechanics among other publications. Your author also had AEB prevent an accident, in his case in an Acura. Bear in mind, we are human, but both Dyer and I are graduates of numerous performance driving schools and have days or weeks of track time per year, often with professional instructors along. We know how to drive safely. Yet, these systems have saved us from crashes.

Related Story: Does Pedestrian Auto Braking Really Work?

Conversely, having tested literally thousands of new vehicles in real-world situations over the past decade, the BestRide staff have had only encountered a single situation where a vehicle braked to a stop when it was not warranted. Our tester Nicole Wakelin reports, “One of the big problems I encounter is when there’s a steep dip, like coming down a steep driveway to enter a flat road that runs perpendicular to the driveway. It actually reads the road as an object in front of the car due to the angle. I nearly got stuck once when a car refused to stop braking!” Nicole reported the incident directly to the automaker for investigation.

Although we have had no near accidents due to false-positive auto-braking, vehicles we test do sometimes apply braking when we would have chosen not to brake. There are two main scenarios in which this occurs. The first is when you are following a vehicle and it is signaling a right turn ahead into a side street. By habit, many drivers will swing wide in the lane and plan to just miss the rear corner of the turning vehicle. This is something a driver can judge by practice. The driver knows the turning speed, knows the closing distance, and can adapt if need be at the last moment. AEB thinks you’re nuts and will brake. It does not fully stop your vehicle. It just slows you so that you will pass safely. Apply gas or turn and it will stop braking.

A second scenario is similar. It occurs on the highway when one is using adaptive cruise control and a vehicle ahead slows. You check your left rear, use a turn signal, and plan to pass the vehicle ahead by a safe distance, but the AEB and adaptive cruise control systems see the vehicle ahead slowing and the systems begin to slow you as well to maintain the pre-set vehicle spacing distance. The braking can feel abrupt, but again, it is not going to stop the vehicle fully, just brake to keep the spacing. If you use the accelerator or turn it will disengage.

With so many vehicles tested by our staff of five weekly testers, and with not a single example of a vehicle braking in a situation in which it would have caused an accident, it is hard for us to provide our own real-world proof that auto-braking can be a hazard. However, we can all report that it can be a hassle.

The warnings that these systems provide are another story altogether. The systems provide so many false positives it is hard to know where to begin listing them. Let’s start with a recent example. We tested a Nissan Maxima that for a full week of testing never squawked at us once. Our next test vehicle then arrived and we drove it just 15 feet before that vehicle provided a false positive alarm in our driveway. This occurred at a speed of about 10 MPH while facing a clear 200-foot driveway ahead. Sadly, this is not uncommon.

One of our staff reports, “I get the false warnings, maybe 35 percent of the time I test a vehicle. There will be literally nothing in front of me, or it’s reading something slightly left or right as being in front of me.” Another reports, “I’ve had the warning light flash for no reason a few times over the last three years, but the brakes have never applied.” Another says, “I have never had brakes apply randomly going forward without a good reason.” Our West Coast team member, Philip Ruth reports that his test area poses a unique challenge to AEB systems. Philip says, “Driving in San Francisco means having press cars stopped mid-way up the Hill because they’re freaked out by a bumper that crested the hill in front.”

Sharp turns on roads with trees, certain glare situations, debris blowing across the roadway ahead, and even when entering a garage are also examples of times when AEB systems have provided us with false-positive alerts but with no braking. John Paul, BestRide test driver and AAA’s Car Doctor reports, “I get many emails and occasional calls on the radio that ‘my forward collision warning light came on or is disabled.” This is usually during heavy rain or snow.”

Our testing and the two new NHTSA recalls do indicate that these systems are not all the same and are not yet perfected. Jessica Cicchino, IIHS vice president for research and an AEB study co-author says that such systems should be standard equipment, but that, “…designers have to be mindful not to build in sensitivities that would irk drivers or put them in potentially risky situations by intervening in situations in which the driver is in control of the vehicle.” We feel that automakers should continue to offer the systems, but should be vigilant regarding reports of trouble and communicate better with owners when trouble does arise. These systems have been proven to reduce accidents. However, if the public or regulators lose confidence in them due to real-world failures, the backlash could be significant.

John Goreham

John Goreham

Leave a Reply