we learn how well a new safety feature on your car really works. It's a scary moment, when you slam on the breaks to avoid hitting the car in front. So how well do the cars that claim to help you... See More
we learn how well a new safety feature on your car really works. It's a scary moment, when you slam on the breaks to avoid hitting the car in front. So how well do the cars that claim to help you stopper form? Abc's david kerley on the test results. Reporter: Have you been in one of these? One out of every three crashes is a rear ender, which is why car makers are adding collision avoidance systems. All right. I'm going to play the distracted driver. Reporter: Tonight for the first time ratings for these systems. Some just beep a warning. Others have what is called auto braking. I'm getting real close to this obstacle. It just takes over everything. That is striking. Just amazing. Reporter: Subaru's out back and legacy got the highest rating in the test, up to 25 miles an hour. But I even took the subaru up to 35 miles per hour. Two cadillacs, two volvos and a mercedes using cameras or radar made it into the insurance institute for highway safety's superior category slowing if not stopping the vehicle. 16 midsize vehicles with auto braking were tested. While they did give a warning, researchers found that not all the vehicles stopped before hitting the obstacle. That is the infiniti jx, which didn't brake enough to brake into a hirer category. Infiniti tells abc news it will study results as quote, we continue to develop future technologies. These systems add about $1,000 or more to the cost of the car. You'd like all manufacturers to make this standard equipment. Exactly. We think it could be reducing a lot of real world crashes, if that were the case. Reporter: Their numbers, a beep or braking in every car could cut a quarter million crashes every year. David kerley, abc news, ruckersville, virginia.
This transcript has been automatically generated and may not be 100% accurate.