DRIVER OF OUR CAR, THE HYUNDAI ELANTRA TOURING, SLOWED TO ABOUT 20-25 MPH TO LET A CAR IN FRONT OF US TURN INTO A DRIVEWAY. DRIVER OF A HONDA CRV TRAVELING BEHIND US AT ABOUT 45-50 MPH DID NOT SLOW AND SLAMMED INTO THE BACK OF US. FRONT SEAT PASSENGER HIT HER HEAD ON THE DASHBOARD RESULTING IN A BRUISE AND BLACK EYE AND WHIPLASH BECAUSE SEAT BELT DID NOT RESTRAIN HER, AND AIRBAGS DID NOT DEPLOY. DRIVER'S SEAT SLID BACKWARDS, LOOSENING HIS SEATBELT. HE HIT HIS HIP AND KNEE ON THE DOOR AND EXPERIENCED WHIPLASH. POLICE ON SCENE LOOKED AT SEATBELTS ON BOTH SIDES AND DETERMINED THERE WERE NO "STOP MARKS" INDICATING THE SEATBELTS HAD ENGAGED. *TR