Crumple zones in cars have long used mechanical bending forces to reduce the crash energy transmitted to vehicle occupants. Now, Mercedes is introducing what it calls an "electronic crumple zone" in the 2009 E- and S-Class. The radar-based "Pre-Safe" system calculates when the car is in danger of crashing into a stopped car or stationary object. When the system detects that the car is approaching an object too quickly, it gives the driver three audible warnings. Then, about 1.6 seconds before the computer assesses a crash is imminent, the car automatically applies the brakes about halfway. If the driver fails to react, the car automatically applies full braking about a half second before impact. Mercedes says the Pre-Safe system reduces impacts by about 10 miles per hour when the driver fails to react. This won't prevent an accident but it will significantly reduce the damage. The system uses two radars with a range of about 90 feet and a more powerful unit with a range of about 200 yards.