WE REAR-ENDED A SEMI TRUCK WHILE DRIVING ON A HIGHWAY AS TRAFFIC BEGAN TO SLOW . THE ENTIRE FRONT END OF OUR VEHICLE WAS BADLY DAMAGED. THE AIRBAGS DID NOT DEPLOY AND THE PRETENSIONERS ON THE DRIVERS SEATBELT DID NOT ENGAGE . THE SPEED AT WHICH WE WERE TRAVELING IS UNKNOWN BUT LIKELY MORE THAN 15 MILES PER HOUR AND LESS THAN 40 MILES PER HOUR. THE DRIVER LOOKED AWAY FROM THE ROAD BRIEFLY AND REAR-ENDED THE TRUCK AHEAD . WE ARE EXTREMELY CONCERNED THAT OUR AIRBAGS AND SEATBELT DID NOT ENGAGE. THE DRIVER HIT HER HEAD ON THE STEERING WHEEL AND THE PASSENGERS KNEES WERE JAMMED INTO THE GLOVE COMPARTMENT.