I WAS TRAVELLING ON THE INTERSTATE AT ABOUT 50 MPH WHEN TRAFFIC CAME TO A SUDDEN STOP. I SLAMMED ON MY BRAKES IN PLENTY OF TIME, BUT I REAR-ENDED THE VAN IN FRONT OF ME. AT THE TIME I THOUGHT I MUST HAVE SKIDDED INTO THE VAN, BUT LOOKING AT THE COLLISION SITE LATER, THERE WERE NO TIRE MARKS.