For over an hour the northbound I-5 was backed up at Clairemont Drive after a vehicle traveling approximately 100 mph slid down an embankment.  Details of the car accident were not disclosed immediately.  It was reported that a man was lying on the freeway around 9:30 p.m. and a black sports car drove off before plummeting down the embankment 10 minutes later.  Traffic was backed up all the way to the I-8.  There was no news on the condition of the man on the freeway, but the CHP sent a technician to a nearby hospital to draw blood for a test.