A fuel truck carrying 1,500 gallons of heating oil overturned on the Southeast-Southwest Freeway near the start of yesterday afternoon's rush hour, backing up traffic into downtown Washington and Northern Virginia.

Authorities initially feared that part of the freeway had been damaged by the truck, which was reported to be leaking heavily. In the end, the spill was limited to about 80 gallons. The truck knocked out the guardrails and a temporary light pole on the bridge over Third Street SE near Capitol Hill.

The driver, who turns 29 today, was hospitalized but not seriously hurt. But commuters and other travelers were delayed as the freeway's eastbound lanes and the tunnels at Ninth Street NW and Third Street NW were closed for periods of the afternoon while workers righted the truck, pumped out the remaining fuel and towed it away.

"I'm going to have to miss class," said Odean Serrano, a NASA manager studying for a doctorate at George Mason University who was stuck in the jam.

Added cabdriver John Sheldon, "A blind man can see that this traffic isn't going anywhere."

The 2:30 p.m. accident occurred in a construction work zone, where the city is rehabilitating the freeway from Second Street to Ninth Street SE.

The speed limit there is 40 mph, and D.C. police said the driver may have been speeding. No charges had been filed as of last night, but the accident remains under investigation, police said. The driver, John Ward Jr., of Huntingtown, told a police officer at the scene that another driver cut in front of him, forcing him to slam on the brakes. There were at least 100 feet of skid marks from the truck, which landed on the driver's side, police said.

Ward was taken to D.C. General Hospital, where a spokeswoman said he was in stable condition. He works for Petro Express Co., a petroleum hauling company in Baltimore.

Larry Parker, of the 300 block of I Street SE, was leaving his job at a landscaping company at Third and G streets SE when the accident occurred.

"Just as I was through the tunnel [at Third Street], I heard a loud noise. I ran back to see, and the truck had flipped over and knocked out the railing," Parker said.

Nearby, at 300 Virginia Ave. SE, Maria Beckham was talking on the telephone. "I heard a loud noise and boom! boom! boom! boom! I said, 'Oh, my God, what happened?' I looked out the window and saw the truck."

Staff writer Emily Wax contributed to this report.

CAPTION: D.C. firefighters clean up oil from a tank truck that overturned on the Southeast-Southwest Freeway, tying up traffic.