The fire is in the engine area which indicates that is where fire originated. I have also seen trailer brakes lock up & driver kept driving so long the heat ignited the tires. This last summer I was on a two lane road & smelled hot brakes that became stronger as I went on. Sure enough in about three miles the rig was on the shoulder with a brake fire. Surely the driver could feel the drag & look in the mirrors & see smoke. I have seen drivers, probably rookies, blow a drive tire & never slow down till the tire next to the blown tire blew also. Recently I saw one that tried to make it to a truck stop & caused damage to the tractor.