Engineers and California Department of Transportation crews have drilled more than halfway through the new tunnels at Devil’s Slide on the San Mateo County coast. The long-awaited twin tunnels are taking shape beneath San Pedro Mountain. They will eventually help to reroute Highway 1 away from the twisting stretch of coastline called Devil’s Slide. Crews expect to punch through the other side of the mountain this time next year, and the tunnels are slated to open in late 2011. When complete, the single-lane passageways will each stretch 4,100 feet, connecting with Highway 1 on a new bridge south of Pacifica.