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Your Automatic Braking System Might Not Stop Your Car

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author photo by Russ Heaps September 2016

Nearly 10 percent of new cars are equipped with automatic braking, a technology that helps drivers stop, particularly in emergencies. If road conditions change in front of the car -- say, if traffic slows suddenly or stops all together -- the system usually issues an audible warning to grab the driver's attention. If the driver still doesn't react or fails to respond quickly enough, the system automatically applies the brakes. So far, so good, right?

The issue with automatic braking, as well as many other driver-assistance aides, is that most drivers assume these systems can fulfill their assigned tasks with complete success. So, in the case of self-braking, the system should bring the vehicle to a complete stop before hitting the object in front of it. But, according to recent tests performed by the national nonprofit car club AAA (Automobile Association of America), that isn't always the case.

AAA discovered that when traveling at a speed of 30 miles per hour, automatic braking brought the vehicle to a complete stop and avoided an accident no more than 60 percent of the time, depending on the vehicle and the type of system it employs. Some systems were only able to stop completely and avoid an accident about 33 percent of the time.

Types of Automatic Braking

Self-braking systems fall into two general categories: those engineered to stop the vehicle completely to avoid a crash and those designed to slow the car down and lessen the severity of a crash. So, by their very design, some systems aren't even intended to bring the vehicle to a complete stop.

According to AAA's research, however, drivers shouldn't even count on those systems designed to avoid a crash to do so 100 percent of the time.

Test Methodology

AAA selected five 2016 vehicles with automated braking systems: the Volkswagen Passat, the Lincoln MKX, the Subaru Legacy, the Honda Civic and the Volvo XC90. The organization performed more than 70 emergency-braking tests on a closed course in California, recording data such as vehicle speed, rates of deceleration and amount of vehicle separation in an effort to mimic real-world driving scenarios. Testing scenarios included static objects, as well as moving traffic.

Key Findings

When operating at speeds of 30 mph or less, vehicles with emergency-braking systems designed to avoid a crash entirely did so about 60 percent of the time. Those systems designed only to reduce crash severity still stopped the vehicle entirely and avoided a collision 33 percent of the time.

In terms of reducing vehicle speed, systems engineered to stop the car completely slowed the vehicle about twice as much as the systems designed to lessen crash severity -- 79 percent speed reduction versus 40 percent.

When approaching a static object at 45 mph, systems intended to completely stop a car and avoid a crash reduced speed by an average of 74 percent and avoided a crash 40 percent of the time, while systems designed to lessen the severity of a crash only reduced speed by an average of 9 percent.

Takeaway

Although automatic-braking systems shouldn't be considered foolproof, even those not engineered to bring the vehicle to a complete stop still serve a purpose. According to AAA, at 30 mph, even a 10-mph speed reduction can lessen the severity of a crash by as much as 50 percent. However, drivers need to be aware of the carmaker's stated limitations for any automatic-braking system.

What it means to you: At this point, driver-assistance technologies like self-braking are just that -- technologies designed to help the driver. They shouldn't be expected to replace the driver. Always stay engaged, no matter the number of self-driving technologies your car may have.

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Your Automatic Braking System Might Not Stop Your Car - Autotrader