Devil’s Slide dangers soon to be bypassed by tunnels

By Robbie Webber
There hasn’t been a new highway tunnel built in California in 50 years, but new tunnels that will provide an alternative to a slide-prone stretch of the Pacific Coast Highway will be very impressive when they open. Built with an Austrian drilling technique, the twin bores feature high-tech safety and design elements, and the tunnels will be monitored by cameras 24/7. Originally scheduled to open in 2010, the tricky geology and location in a seismic zone pushed construction back. The tunnels are now completed, but final tests are being run on the cutting-edge technology inside the bores.
Designed to withstand the strongest earthquakes in area, the 4,200-foot tunnels will allow drivers to avoid a stretch of Highway 1 that is known as the Devil’s Slide. And it has indeed slid into the ocean nine times since it was built in 1937, once closing the road for four months. In addition to the chance of washouts, the road has seen its share of head-on crashes and drivers going over the cliff.
The new tunnels are equipped with carbon monoxide and nitrogen oxide detectors, fans that can vent the tunnels in seconds, call boxes, and fireproof chambers along the entire length. The Caltrans project page offers a peek inside and aerial photos of the spectacular location. In addition to the bores themselves, the project required a 1,000-foot bridge 125 feet over a valley on the northern end.
A safe and reliable connection along this part of the California coast is a goal not just for Caltrans, but also for the towns in San Mateo County south of the Devil’s Slide area. Commuters drive north to San Francisco during the week and tourists drive south on the weekends to the scenic areas along the coast. When the road is closed, a seven-mile segment along the coast becomes a 45-mile detour inland, and the local economies of the coastal communities suffer.
Once the tunnels are open, 1.2 miles of roadway will become a pedestrian and bicycle path and park. One regular roadway user looks forward to the transformation. “It’s a wonderful, beautiful view, and we really don’t get to see it while we’re driving by.”
Robbie Webber is a Senior Associate at SSTI.