Devil's Slide Tunnel?-?Pacifica, Calif.
Located along the coast between Pacifica and Montara, the Devil's Slide portion of Route 1 has a long history of closure due to rockslides and land slippage since its construction in 1937. The $268 million project constructed tunnels that are approximately 4,100 feet long, 30 feet wide, 22 feet high and 60 feet apart to allow motorists to bypass these major slide areas. The project scope included roughly 225,000 cubic yards of excavation and 80,000 cubic yards of tunnel concrete.
The tunnels were constructed through granitic, sandstone and shale formations using the New Austrian Tunneling Method, which relies on inherent rock strength for support. Kiewit is one of the few contractors in the U.S. to use this type of tunneling method.
Key features of the tunnels include 32 jet fans for ventilation; fire detection and suppression system; carbon monoxide and nitrogen oxide detection systems; closed-circuit television monitoring and emergency call box telephone systems; electronic message signs displaying safety and advisory information; and an over-height vehicle detection system. In addition, nine cross passages connect the tunnels for escape and emergency purposes. Crews also excavated three emergency vehicle storage areas between the tunnels.