I STRUCK A VEHICLE THAT HAD STOPPED SUDDENLY IN FRONT OF ME. I WAS ABLE TO DECELERATE TO ABOUT 30 MPH BEFORE THE COLLISION. DRIVER'S FRONT AIR BAG DEPLOYED WITH SUCH FORCE, OR WITH SUCH INCORRECT TIMING, THAT I SUSTAINED A COMPLETE AND PARTIALLY DISPLACED FRACTURE OF THE STERNUM. IN SEARCHING THE MEDICAL LITERATURE, THIS IS AN INJURY USUALLY ASSOCIATED WITH NOT WEARING A SEAT BELT, WHICH I WAS, OR WITH STRIKING THE STEERING WHEEL, WHICH I DID NOT. THERE HAD BEEN NO PRIOR ILLUMINATION OF AIR BAG WARNING LIGHTS, OTHER THAN THE TEST ILLUMINATIONS WHEN THE CAR IS STARTED. *TR