A 2-inch-wide bolt closed a Baltimore County bridge yesterday.

When an engineer hired by the Baltimore County government inspected a bridge in the Oella area, he noticed the bolt protruding from the structure.

The problem looked serious enough to prompt county officials to temporarily close the bridge, a two-lane, 100-foot-long metal span on Westchester Avenue over a bicycle trail.

"The bridge wasn't close to collapsing, but this was a critical piece in the bridge because of the kind of design it is," said David Fidler, a spokesman for the county's Department of Public Works.

He said the span is an acro-bridge -- a prefabricated structure -- which is kept together partly by pins.

The bridge was closed for four to five hours as engineers worked on pounding the pin back into place. By 1:30 p.m., the span was reopened.

Fidler said the problem was discovered as part of a routine inspection. He said the county has not changed its bridge inspection program since the collapse in early August of a Minnesota bridge into the Mississippi River because the program already included every possible precaution.

The Westchester Avenue bridge is one of 480 in the county. The county hires private contractors to inspect each bridge at least every two years.

The contractors report any needed repairs, assigning them one of three rankings: immediate, priority or routine. County engineers often perform their own inspections after the contractors submit their reports.

The Westchester Avenue bridge was built in 1988 and runs over the Ravine Bicycle Trail dozens of feet below. The bridge is in a leafy neighborhood of Colonial houses, just north of Frederick Road and near the Howard County border.

Last year, an engineer performed a routine inspection of the bridge and noted on his report that a pin was sticking slightly out of the structure. The matter was not considered urgent, Fidler said.

"We knew that it was working its way out, but we thought we had time with it," he said, adding that engineers have been "keeping their eye on it."

Yesterday morning, during another routine inspection, an engineer noticed that the pin was sticking out even more. Fidler said it had moved out more quickly than engineers had expected.

"The repair is fairly simple: It's a matter of heating the bolt up, scraping up the rust, and some kind of hydraulic tool pounding it back into position," Fidler said.

Engineers initially expected the task to take at least a day, with the bridge reopening this morning.

"We managed to take care of the task in really a few hours," Fidler said.

josh.mitchell@baltsun.com