WHILE STOPPED AT A LIGHT, WE WERE REAR-ENDED BY A 1984 CHEVROLET VAN. BOTH PARTIES IN THE TRUCK WERE WEARING A SEATBELT AT TIME OF ACCIDENT. BOTH FRONT 50/50 BENCH SEAT BACKS, ONLY ALLOWED TO FUNCTION LIFTING FORWARD, COLLAPSED BACKWARDS. THIS CAUSED TWO PASSENGERS TO FALL BACKWARDS TO THE EXT. CAB PORTION OF THE TRUCK, WHERE NORMALLY OUR KIDS SIT. AT ONLY 6'0" TALL, MY HUSBAND'S HEAD WENT THROUGH THE BACK WINDSHIELD OF THE TRUCK CAUSING NECK AND BACK INJURIES.