Traffic flowed normally across Bay Area bridges during the morning commute Friday, despite threats of a terrorist attack.

But security was notably increased, as National Guardsmen toured the bridges early in the morning to familiarize themselves with overlooks, buildings and other features.

Many commuters opted not to alter their routines, saying the warning wasn't specific enough to take seriously.

"I consciously wouldn't change my plans unless it were an immediate threat," San Francisco resident Larry Odhner told the San Francisco Chronicle as he prepared to drive across the Golden Gate to meet his brother.

Both Southern California bridges had moderate traffic with no reported problems Friday morning. At Vincent Thomas, camouflaged National Guard troops carrying M-16's rifles stood below the spans.

"This bridge is probably as safe as it's ever been, said Janice Hahn, a city councilwoman who represents Los Angeles' Harbor district. "But if people don't feel comfortable driving on the bridge I want to make sure they take alternative routes and those routes are open and clear and also patrolled."

Although hundreds of threats have been called in to authorities around California since the Sept. 11 terrorist attacks, this is only the second one to have been judged credible, Gov. Gray Davis said.

Security around the bridges has been heightened since Sept. 11. The extra security includes flyovers and a greater presence by the Highway Patrol and Coast Guard.

After the specific bridge threat, Davis said security has been stepped up even more, with National Guard troops being posted at both ends.

California Highway Patrol Commissioner Spike Helmick stressed that the public shouldn't be fearful.

"Those bridges are safe. We encourage people to use them. In fact, I'll be driving over them tomorrow on several occasions," Helmick said.

Officials representing the agencies that operate the bridges said they are taking the threats seriously.

Sonoma resident Constance Kilgore commuted by bus across the Golden Gate Bridge on Friday to her work in San Francisco.

"I’m angry that I'm feeling anxious and afraid. Every time I cross the bridge I think about the terrorists and the way they are going to do it," she said. "I don't think our security is good enough. There's no way they can monitor everything."

Many others crowded onto the subway.

Taking Bay Area Rapid Transit means tacking an extra 45 minutes onto her commute, but film editor Stephanie Shallberg of Lafayette says she'll take the train rather than drive until year's end.

"There was no way I'd drive over the Bay Bridge," she said Friday morning. "On my way home last night, I thought I was going to pass out."

Pedestrians and cyclists are still allowed on the Golden Gate Bridge. On the vehicles-only Bay Bridge, officials were inspecting identification badges and have welded shut potential access points to prevent trouble.

"We feel we're well-prepared for any nefarious and criminal actions," said Jeff Weiss, spokesman for the San Francisco-Oakland Bay Bridge.

Janet Vuoso, who lives near the Vincent Thomas bridge, said she is concerned about the safety of her family.

"I'm going to go home and tell my daughter to stay away from the bridge," said Vuoso, who teaches at a private medical school. "I don't think it's a question of if, but a question of when."