A tractor-trailer slammed into two highway-painting trucks parked on the I-95 shoulder near Lorton yesterday, injuring three persons and backing up traffic for more than four hours, according to Virginia State Police.

The accident occurred shortly after 8 a.m., when the tractor-trailer, driven by Richard Cumberledge, 35, of Chester, W.Va., and owned by CRST Inc. of Cedar Rapids, Iowa, was traveling south on the highway shoulder, and struck the paint trucks, knocking them into an embankment, police said.

Cumberledge was taken by helicopter to Fairfax Hospital, where he was listed in fair condition. Police said they did not know why the truck was in the shoulder lane. The cause of the accident is under investigation.

Also injured was John W. Turner, a 41-year-old South Carolina man, who was working underneath the highway-painting trucks, which are owned by Allied Striping, police said. Turner had partially emerged from under the trucks when his wife saw the tractor-trailer coming and screamed for him to move, police said. He was taken to Mount Vernon Hospital, where he was being treated for broken ribs, police said.

A third man, James D. Bauer, who had been sitting in another of the paint trucks at the time of the crash, was treated at the scene for a cut arm, police said. No address was given for Bauer.

As a result of the accident, police closed I-95 southbound from the Capital Beltway to Pohick Road, and one northbound lane was closed to make room for rescue vehicles.

The lanes weren't fully reopened until 12:30 p.m., police said. One traveler observing the stalled traffic said that some of those waiting for the accident to be cleared had climbed on their car roofs to sunbathe.

Police said that despite efforts to control congestion, traffic spilled over onto the eastbound and westbound lanes of the Capital Beltway in the Springfield and Franconia areas.

The accident forced the postponement until later this week of car pool restrictions for southbound I-95, according to the Virginia Department of Highways and Transportation. The restrictions were to start last night.

"That paint crew was trying to finish some of the last-minute line work that they couldn't do over the weekend because of the rain," said Marianne Pastor, department spokeswoman. "As a result of the accident, the lane markings did not get done."