WAS DRIVING VEHICLE WHEN ANOTHER VEHICLECROSSED FROM ANOTHER LANE IN FRONT SUDDENLY. CONSUMER APPLIED THE BRAKES & REAR ENDED VEHICLEIN FRONT. UPON IMPACT WITH VEHICLE, DRIVER'S SEAT BELT FAILED TO LOCK UP TO RESTRAIN DRIVER. SEAT BELT BUCKLE LOCKING MECHANISM BROKE. DRIVER WAS THROWN FORWARD, BUT NOT INJECTED. DRIVER SUFFERED WHIPLASH & RELEASED FROM EMERGENCY ROOM. *AK