 It was a little after 6 o'clock this morning that a tractor-trailer caught on fire on the outer loop of the Beltway in Maryland. It caused major traffic delays. Montgomery County Fire and Rescue spokesperson said it appeared a vehicle collided with a tractor-trailer then left the scene. Then a big rig caught on fire because of the ruptured saddle tank. About 15 to 20 barrels of crushed tungsten metal spilled onto the roadway of 495.