WHILE DRIVING OUR 2010 TOYOTA PRIUS II ON THE INTERSTATE WE BEGAN NOTICING A BURNING SMELL. THEN, THE ABS LIGHT ILLUMINATED ON THE DASHBOARD. WE PULLED ONTO AN OFF RAMP AND AS WE SLOWED THE VEHICLE DOWN SMOKE BEGAN COMING FROM UNDER THE HOOD. WE DROVE VERY SLOWLY DOWN THE ROAD AND THE SMOKE BECAME MORE PREVALENT. WE TURNED ON A SIDE STREET AND MY HUSBAND PUT THE VEHICLE IN PARK, GOT OUT, WALKED TO THE FRONT, AND NOTICED THAT THE PASSENGER FRONT HEAD LAMP WAS MELTED AND THERE WAS A FLAME. WE QUICKLY GOT OUR FAMILY OUT OF THE CAR (2 KIDS IN CARSEATS IN THE BACK). WE MOVED AWAY FROM THE VEHICLE AND THE FLAMES BECOME LARGER AND LARGER. WE CALLED 911 AND THE HOOD WAS ENGULFED IN FLAMES BY THE TIME THE FIREFIGHTERS ARRIVED. THEY WERE ABLE TO PUT THE FIRE OUT QUICKLY, SO IT DID NOT SPREAD INTO THE FRONT CABIN OR REAR OF THE VEHICLE. WE HAD NOT HAD ANY RECENT WORK DONE AND THE VEHICLE WAS FULLY OPERATIONAL UNTIL THE TIME OF THE FIRE. WE HAD NOT BEEN EXPERIENCING ANY PROBLEMS PRIOR TO THIS INCIDENT.