On expressway traveling through Atlanta, changing lanes with plenty of clearence using signal at approximately 55 mph when suddenly alarm sounded and breaking system engaged bringing car to almost complete STOP. COULD NOT ACCELERATE and fortunately made it to berm area without causing SERIOUS accident. Turned engine off and restarted vehicle and continued on my way. Had vehicle checked at dealership and they said all checked out and we found no diagnostics problem. Also werent able to duplicate incident. I hope to God I AM UNABLE to duplicate the incident and cause fatalities including myself.