TRANSMISSION DISENGAGED THEN DOWNSHIFTED (1ST) WHILE DRIVING. BRAKES ENGAGED. CAR CAME TO VIOLENT HALT , THEN CAR AND PASSENGERS WERE LURCHED BACK & FORTH UNCONTROLLABLY WITHOUT OPERATOR INPUT, RPMS ERRATIC UNTIL KEY REMOVED. FREEWAY INCIDENT WOULD HAVE RESULTED IN FATALITIES. CAR WAS NOT DRIVABLE, MFG DENIED SIMILAR CLAIMS, SEE NHTSA ITEM # SB605899. TRAUMA OF EVENT HAS RESULTED IN INABILITY TO DRIVE VEHICLE (CONCERN FOR SAFETY AND FEAR OF REOCCURANCE).