A highway used as a major gateway to the District by 100,000 motorists a day was shut down yesterday after a truck struck an overpass, causing virtual gridlock on the eastern approaches to the city.

The flatbed was southbound on Kenilworth Avenue about 7 a.m. when construction equipment it was carrying scraped chunks of concrete from the Eastern Avenue overpass.

After inspection of the bridge, transportation officials said last night that the damage was not as serious as feared, and they hoped to fully reopen Kenilworth Avenue, also known as Route 295, by this morning's rush hour.

"There's a lot more redundancy in the construction than we thought," said Bill Rice, a spokesman for the D.C. Department of Transportation.

After determining that there was more steel supporting the bridge than first thought, authorities had reopened the northbound lanes by 7 p.m. and were working on the southbound lanes last night.

Rice said a net would be stretched just beneath the bridge as a precaution against crumbling concrete.

No one was injured in the accident, but closing a six-lane artery at the peak of the morning rush triggered a ripple effect that soon had traffic stacked up on every road leading into the city from the east. Kenilworth and Eastern avenues remained closed throughout the day, and the evening rush hour proved a recurring nightmare for those who had weathered the morning snarl.

Rice said the clearance of the overpass is 14 feet, 2 inches. He said the construction equipment the truck carried extended to a height of 15 feet. Any truck above 13 feet, 6 inches tall is required to have a special permit and a prescribed route to travel in the District, Rice said.

"It's fortunate nobody got hurt," said Capt. Dierdre Porter of the 6th Police District. "It could have been worse. Those were some big boulders out there."

Behind the truck was a car driven by Gerson Kuhr of Springfield. Chunks of debris, some the size of watermelons, rained down on the vehicle, he said last night. "It was a bit unnerving."

The car was dented. Its windshield cracked, he said, but did not shatter. Although he was "just a bit shaken up," he said, he was not injured.

His wife, Cindy, said he told her it was the kind of experience "in which you see your life flash before your eyes."

Police said the truck is owned by Asher Construction Inc. Michael Asher, who owns the company, which specializes in highway and bridge construction, could not be reached last night.

The truck driver, David Ballentine, 43, of Westminster, Md., received a traffic citation, according to Sgt. Joe Gentile, a spokesman for the D.C. police department. Reached last night, Ballentine declined to comment.

Rice said the worst damage was caused by the initial impact on the face of the bridge, but it was compounded when Ballentine scraped through to the other side.

Rice said the District's Transportation Department sometimes bills motorists for damage they cause to roads and other infrastructure. Although he could not offer specifics yesterday, he said "we do have a mechanism" for determining whether a driver should be held responsible for roadway damage and how much the bill should be.

Staff writers Steven Ginsberg, Paul Duggan, Del Quentin Wilbur, Allan Lengel and Martin Weil contributed to this report.

Workers examine where chunks of concrete dropped from the Eastern Avenue overpass after a truck carrying construction equipment hit the bridge and continued through.Workers shut southbound lanes of Kenilworth Avenue after the truck shown above hit the Eastern Avenue bridge.Kenilworth traffic is rerouted to avoid the bridge. Kenilworth and Eastern avenues were shut for much of the day.