DRIVER'S SUBARU WAS STRUCK FROM BEHIND BY A BOX TRUCK WHILE STATIONARY ON A HIGHWAY (DRIVER HAD STOPPED JUST SHORT OF A MULTI-CAR COLLISION BUT THE BOX TRUCK BEHIND HER WAS UNABLE TO STOP); BOX TRUCK PUSHED THE SUBARU INTO THE CAR IN FRONT. DRIVER'S SEATBELT WAS ON, BUT DRIVER'S CHEST STRUCK THE STEERING WHEEL AND HER HEAD POSSIBLY HIT THE SIDE WINDOW. AIRBAGS DID NOT DEPLOY AND SEATBELT DID NOT STOP DRIVER FROM STRIKING STEERING WHEEL. ALSO, THE EMPTY FRONT PASSENGER SEAT ROCKETED FORWARD ON ITS RAILS ALL THE WAY TO THE FRONT, AND AT LEAST THREE HINGES FLEW OFF THE PASSENGER SEAT RAIL MECHANISM.