Traffic was stalled or stopped last night on two major interstates in Maryland after a man perched on an overpass and threatened to jump, Maryland State Police said.

Motorists were delayed at various times on Interstate 95 and nearby sections of Interstate 495 after police found the man on the overpass that carries Old Gunpowder Road across I-95 in Calverton in Prince George's County, state police said.

"It's a slow go," said Chuck Gischlar, a spokesman for the Maryland State Highway Administration. "People are really stuck out there."

The man climbed up on the overpass sometime before 8 p.m. Authorities shut down the northbound lanes of I-95 and brought in negotiators. After about three hours, authorities managed to get the man down and took him to a hospital.

But for much of the night, motorists on nearby sections of the Capital Beltway reported that traffic was flowing extremely slowly as the effects of the I-95 shutdown rippled outward.

About 9:30 p.m., authorities shut down all lanes of I-95. They explained that the man was shifting his position on the overpass and that it was no longer sufficient to halt traffic on only one side of the highway, which is a major north-south route on the East Coast.

Last night, while negotiations continued and the man kept moving about, Gischlar said that northbound lanes reopened but southbound lanes were still shut.

At that point, traffic was backed up on both sides of I-95.

"We're looking at a couple of miles in each direction," Gischlar said.

He said authorities were attempting to mitigate conditions by using electronic message boards that alerted motorists to detours. In addition, he said, traffic signals were reprogrammed to speed the flow on Route 1, one of the recommended alternate routes.