I was driving approximately 75mph on the interstate. 3 hrs into my trip I started feeling hot so I turned the a/c up. In my peripheral vision I saw orange and thought a car was beside me on fire. Immediately I realized it was my vehicle. I immediately slowed and came to a stop. I put it in park and opened the door. By the time I started to exit there were flames higher than the rear windows. A car that was behind me stopped. They said about a mile back there was a spark under the car by the rear tire. Then it went up in flames.