The contact owns a 2008 Mercury Sable. The contact stated their daughter was driving at 55 mph, when the driver was approaching an intersection at a red light the driver depressed on the brake pedal and the brake pedal went straight to the floor and the vehicle could not stop causing the vehicle to hit the vehicle in front of them in the rear. The air bags did not deploy. The driver does not remember if there was any warning light illuminated on the vehicle. The crash caused damage to the front bumper and pushed in the front grill and hit the radiator of the vehicle. There were no injuries reported. A police report was filed. The contact was a former mechanic and inspected the vehicle but could not diagnose the failure, but was concern that there was an issue with anti- lock brake system. The vehicle was not diagnosed or repaired. The manufacturer was made aware of the failure. The failure mileage was approximate 160,000.