Adopted on 06/30/1987
SEPTEMBER 6, 1985
NTSB NUMBER: HAR-87/02*
NTIS NUMBER: PB87-916204
About 12:40 p.m., e.d.t on September 6, 1985, a 1902 GMC 2-axle truck fitted with a 1973 MC-331 cargo tank overturned while traveling southbound on the Capital Beltway, 1-95, near Largo, Maryland. The 2,500-gallon capacity cargo tank contained about 1,375 gallons of propane. The Poist Gas Company truck was traveling between 50 and 55 mph when, according to the drivers the steering wheel started shaking violently and "flew out of my hands." The driver stated that he took his foot off the accelerator but did not brake because be believed that one of the vehicie's tires was experiencing a blow out. The truck veered across the right paved shoulder of the highway and onto a grass shoulder. It then traveled 300 feet down the grass shoulder until the driver steered the truck back to the left to avoid hitting a tree. The truck slipped the north end of a guardrail when it reentered the paved shoulder of the highway as the driver tried to regain control of the truck. The truck then traveled 510 feet down the paved shoulder and the right travel lane of the highway before rotating clockwise about 80" and overturning on Its left side. The vehicle continued to rotate another 100'* as it slid 400 feet down the highway on Its left side. The truck came to rest facing north (180'* opposite its original direction of. travel) with the top of the cargo tank parallel with and against the guardrail At the time of the accident the roadway was dry and the weather was clear.
The Capital Beltway is an 8-lane asphalt-paved highway which encircles Washington, D.C. It has a large grass median strip dividing the four southbound lanes from the four northbound lanes in the area of the accident. Each lane Is 12-feet wide, and the southbound lanes are bordered on each side with 9-foot wide shoulders. The right (outside) shoulder on the southbound side is bordered by a W-beam guardrail extending for 436 feet along the accident site. The roadway was repaved about 1 year before the accident.
A motorist traveling behind and to the left of the truck estimated its speed to be about 50 mph when he saw the left front wheel of the truck shimmy just before the accident; a few seconds later he saw the truck go off the right side of the road. He recognized that the truck was transporting propane and saw the truck catch fire immediately after sliding to a stop. He said that the fire Initially started behind the cab of the truck near the propane fuel tanks, and that It later spread back to the cargo tank.
Accident Number: DCAA-85-HZ-008