AAA has tested reverse automatic emergency braking, known as AEB, and the results are in. 

AEB is designed to automatically activate a vehicle's brakes when it senses a rear crash. According to AAA, it only prevented a crash in ½ of their tests when a pedestrian was standing behind the car. 

When it was traffic moving behind a car, it only prevented a crash in 2.5% of tests. 

"It's important that drivers realize this that the technologies are not foul proof and they remain alert, particularly backing up we've seen unfortunately some back over crashes where children where playing behind a vehicle that was in the driveway and a parent came out and jumped in the vehicle and tragically backed right over the child  so it's important that drivers do walk arounds like pilots do with planes." said Robert Sinclair of AAA Northeast.