A tractor-trailer caught on fire on the Interstate 495 Outer Loop in Montgomery County, Maryland, on Sunday morning, causing major traffic delays.

Montgomery County Fire and Rescue spokesman Pete Piringer said it appeared that an unknown vehicle collided with a tractor-trailer and then left the scene.

The tractor-trailer then caught on fire because of a ruptured saddle tank, Piringer said.

About 15 to 20 barrels of crushed tungsten metal spilled onto the roadway of I-495 in the area of Bradley Boulevard and Interstate 270, spreading debris into the roadway and causing “slick road conditions,” he said.

The WTOP Traffic Center reported at 10:44 a.m. that all lanes were open to traffic again, after vehicles had been diverted around the crash on The Beltway Outer Loop between Old Georgetown Road and the “big curve above the spur” since 6:22 a.m.

Listen live to WTOP for traffic and weather updates on the 8s.