TRAVELING EAST ON I20 OUTSIDE OF COLUMBIA, SC APROX. 3:30AM STRUCK A DEER AND PULL OVER ON EMERGENCY LANE ON AND OFF RAMP. PARK VEHICLE AND GOT OUT TO EXAMINE THE DAMAGE. WALKED AROUND VEHICLE LOOKING AT DAMAGE AND AS I OPENED DRIVER DOOR TO GET FALSH LIGHT TO LOOK UNDERNEATH VAN FOR DAMAGE USED FLASH LIGHT TO LOOK AT DAMAGE AND AS I GOT BACK UP TO GET IN VAN I STEPED UP ON RUNNING BOARD ON DRIVER SIDE TO GET BACK IN VEHICLE AND VEHICLE LUNGED BACKWARDS THROWING ME TO GROUND.DRAGING ME APROX. 20 FEET.I LET GO OF VAN TO ROLL AWAY FROM VEHICLE. VAN STRUCK RETAINER WALL AND STOPED.*AK