OAKLAND -- Under the cover of darkness, a new breed of thieves has been ripping off guardrails on some of the Bay Area's most dangerous roadways to turn them into cash as prices in the scrap aluminum market continue to go up, according to Bay Area transportation officials.

Caltrans officials say the thefts were not only endangering drivers' lives, but also costing taxpayers thousands of dollars in replacement costs.

"This is a huge problem," said Caltrans spokesman Jeff Weiss. "There's hundreds of feet of guard rail that's being stolen every night."

One of the latest locations struck was on the Moraga Ave. exit along Highway 13 in the Oakland hills.

"It's a major undertaking…to go and steal a guard rail," Weiss said. "But apparently aluminum is so expensive now that it's a good business to be in. "

Mike Anglin says he drives by the exit every day and recently started to notice guardrails disappearing.

"I'd come home at night and see them there and the next morning take the kids to school and they'd be gone," he said.

Caltrans said guard rails were being stolen all over the Bay Area. On the peninsula, a favorite target is along Highway 92. In the East Bay, Interstate 880 exits at 66th avenue, Highway 580 at Keller and on Highway 24 were also targeted.

On Wednesday night, thieves stole a bunch of the tubular railing on the bridge just before the Caldecott Tunnel.

"If a driver were to strike that, the guardrail would just come off and they'd go flying off the bridge or into a tree or something like that," Weiss said. "It's a safety hazard and it's very expensive."

Caltrans has joined forces with the California Highway Patrol in sting operations to try to catch the thieves. Local scrap metal yards have also been alerted to be on the lookout for people bringing in guard rails.

However, the efforts so far have come up empty of suspects.

"It would seem like it would be easy to catch these people, but they have a method of operation that makes it difficult to catch them," Weiss said. "And there are so many bridges that you can't have your eyes on them at all times."

Caltrans says its crews only work on guard rails during daylight. Officials were asking the public to call police if you see someone working on guard rails at night.