Tons of gravel spilled onto Route 7 in Loudoun County from an overturned truck early Monday, blocking all or part of the road for about four hours, authorities said.

The incident occurred at the intersection with Belmont Ridge Road in the Ashburn area, the county sheriff’s office said.

The dump truck overturned when it tried to avoid a collision with a car that was traveling east in the westbound lanes, said Kraig Troxell, a spokesman for the sheriff’s office.

He said the spill occurred just before midnight on Sunday night, and the road did not completely reopen until about 4 a.m. Monday.

The exact amount of gravel that spilled was not clear. According to figures published online, many standard dump trucks can carry 15 or 20 tons of gravel, which can weigh about one and a half tons per cubic yard .