They might be landmarks, marvels of the modern world, great places to see the skyline and the fastest way to get to work, but California commuters have become bridge-phobic ever since it was revealed that the state's spans might be terrorist targets.

On Thursday, Gov. Gray Davis issued warnings that terrorists could be aiming to destroy the San Francisco's Golden Gate and Bay bridges, theVincent Thomas Bridge at the Port of Los Angeles and the Coronado Bridge in San Diego. Although the FBI said the threat was uncorroborated, Davis told The Associated Press he felt he had an obligation to tell the public.

Traffic was off more than usual for a Friday on the four bridges Davis singled out.

Over the weekend, San Francisco merchants complained that even locals were staying away.

"Business is really down," said Barry Vont, who owns a luggage shop at Fisherman's Wharf. "They don't want to drive over the bridge."

Meanwhile, mass transit alternatives, especially in the Bay Area, saw jumps in ridership.

They were to be joined on Monday by Sondre Skatter, 31, a computer programmer who lives in Berkeley and commutes to San Francisco. He said that after talking to his wife, he'll stop driving and start taking the train.

"It's not a big sacrifice, I guess," Skatter said. "This specific warning about the bridges I take seriously."

Commuters are going to work by boat, too. The number of ferry passengers into San Francisco was up Friday, both from Oakland in the east and Marin County in the north. But the system was far from maxed out.
On an average day, the first six runs of Alameda Ferries' boats would carry 500 passengers from Oakland and Alameda. On Friday, there were 900 passengers.

"We have room for people," said Ernest Sanchez, manager of Alameda Ferries. Should demand begin to swell, he said, the line could add charter boats.

Several more ferry runs into San Francisco will be added Monday from Marin County. Ridership surged Friday from 1,600 to nearly 2,900 people during the morning commute, according to Mary Currie, spokeswoman for Golden Gate transportation district.

They're also coming by train. Extra runs are also planned for the Bay Area Rapid Transit commuter train.

Normally, about 40,000 people catch BART trains into downtown San Francisco, according to BART spokeswoman Vicki Wills. The daily average nudged up 2,000 people Friday, when BART ran some extra trains.

In San Diego and Los Angeles, the bridges are not major commuter arteries so the disruption has been minimal.

Government planners are revisiting lessons learned after the 7.1 Loma Prieta earthquake snapped off a slab of the San Francisco-Oakland Bay Bridge in 1989, closing it for 33 days.

That closure turned out to be a boon to the region's commuter train network, which experienced a sustained rise in ridership. The earthquake also resurrected the trans-bay ferry service from Oakland that has survived to today.

"God willing we won't have to use them in a crisis, but I think it's a good thing for people to know that ... there's a lot of travel options," said Randy Rentschler of the Bay Area's Metropolitan Transportation Commission.

In Oregon, where the alert had triggered additional security precautions at some of the most heavily traveled bridges, all was quiet on Sunday.

In Washington, Pierce County Emergency Management reported no problems with the state's only suspension bridge, the Tacoma Narrows Bridge, but special patrols continue there.

The Associated Press contributed to this report.