Beginning at about 2 a.m. today, traffic was permanently redirected away from a notorious cliffside stretch of state Highway 1 south of Pacifica and steered instead into the Tom Lantos Tunnels, CHP Officer Mike Ferguson said.
There have been no reports of any problems, he said.
The tunnels, a pair of north- and southbound bores that run 4,200 feet through San Pedro Mountain, are California's longest tunnels and are the first to open in the state since the Caldecott Tunnel was unveiled in Oakland in 1964, according to Caltrans.
The cost of the project, which took more than six years to complete, was approximately $439 million. More than 21,000 truckloads of dirt and rock was removed from the mountain during construction, Caltrans officials said.
The tunnels replace a nearly mile-and-a-half stretch of steep and winding Highway 1 above the Pacific Ocean that has long been prone to crashes, landslides and long term-closures.
That section of highway is slated to be converted to a hiking and biking trail that will be maintained by San Mateo County.
The tunnels were named for the late Congressman Tom Lantos.
