TRAVELING S. ON I93 WITH CRUISE CONTROL ENGAGED AT SPEED LIMIT. EXIT AT #42 & TAPPED BRAKE TO DISENGAGE SPEED CONTROL. NO RESPONSE! CAR CONTINUED UP RAMP TOWARDS 5 PM TRAFFIC. BRAKES DID NOT AFFECT SPEED AS CONTROLL STILL ENGAGED. TURNED OFF IGNITION JUST BEFORE ENTERING RT 302 INTERSECTION, ATTEMPTING TO AVOID HITTING OTHER VEHICLES. STRUCK MEDIUN SIDEWAYS, CAR ALSO HIT I93 SIGN. STOPPED AT END OF MEDIAN. *AK