WHILE DRIVING IN THE PASSING LANE ON THE HIGHWAY ON MY WAY HOME FROM WORK I BEGAN TO SMELL SMOKE. I INITIALLY THOUGHT IT WAS SOMEONE ELSE'S BRAKES UNTIL I BEGAN TO SEE SMOKE COMING THROUGH THE INTERIOR PANELS OF MY VEHICLES. LUCKILY, THE VEHICLES NEAR ME NOTICED THE SMOKE AND SLOWED DOWN SO THAT I COULD GET OFF THE ROAD. ONCE PULLED OVER I WENT TO THE FRONT OF THE CAR AND FELT THE HOOD BUT IT DID NOT FEEL HOT BUT WHEN I LOOKED UP I NOTICED THE SMOKE WAS COMING FORM THE TRUNK. I WENT TO THE BACK OF THE CAR, OPENED THE TRUNK AND NOTICED FLAMES COMING FROM THE CAR BATTERY COMPARTMENT (NOT THE HYBRID BATTERY). I TRIED TO SMOTHER THE FIRE WITH A SHEET BUT WAS UNSUCCESSFUL. I REALIZED THE FLAMES WERE MOVING DOWN THE SIDE TOWARD THE FUEL TANK AND STEPPED AWAY TO CALL 911. WITHIN MINUTES THE FIRE SPREAD THROUGH MY TRUNK TO THE BACKSEAT OF THE VEHICLE AND COMPLETELY ENGULFED THE VEHICLE.