 This is Washington's news traffic and weather station, WTOP. WTOP News. 923, a tractor-trailer caught fire on the outer loop of the Beltway in Maryland this morning. It caused major traffic delays. Montgomery County Fire and Rescue says it appeared that a vehicle collided with a tractor-trailer then left the scene. The big rig caught on fire due to a ruptured saddle tank. About 15 to 20 barrels have crushed.