AIR BAG DID NOT DEPLOY AFTER REAR END IMPACT FROM A 1 1/2 TON BOX TRUCK AND SUBSEQUENT IMPACT INTO ANOTHER PARKED VEHICLE DIRECTLY IN FRONT OF THE IMPACTED VECHICLE, PROBABLY AT A HIGH RATE OF SPEED FROM PARKED TO IMMEDIATE ACCELERATION. AIR BAG DID NOT DEPLOY UPON IMPACT INTO CAR DIRECTLY IN FRONT OF IMPACTED VEHICLE. ALTHOUGH SEAT BELTS WERE USED, IN A REAR END IMPACT, THE THRUST OF WEIGHT IS TO THE REAR WHICH MAKES SEAT BELTS FUNDAMENTALLY USELESS IN RESTRAINING BODY WEIGHT TOWARDS THE REAR. ADDITIONALLY, IMPACT WITH THE VEHICLE DIRECTLY IN FRONT OF ME RESULTED IN 200 POUNDS OF WEIGHT SUDDENTLY AND DRAMATICALLY BEING THRUST FOWARD WHICH DID NOT PREVENT INJURY TO MY HEAD, BACK, LEG AND ARM.