Welcome to Caltrans District 4

Devil's Slide Project | Tunnels


Tunnel boring progressed from south to north using excavation techniques that relied on inherent rock strength for support - known as the New Austrian Tunneling Method. Both tunnels were bored at the same time, one tunnel face approximately 60 yards ahead of the other. Estimated cost for the tunnels is $439 million. Key features include:

  • Twin bores approximately 4,200 feet long and 30 feet wide.
  • One vehicle lane and shoulder in each tunnel.
  • 11 cross linking passages and 3 underground equipment rooms
  • Day / night lighting system with brightness transition at each end
  • Ventilation provided by 16 jet fans, 3.5 feet diameter, in each tunnel.
  • State of the art fire detection and suppression system
  • Carbon monoxide & Nitrogen oxide detection system
  • CCTV monitoring and emergency / call box telephone systems
  • Electronic message signs displaying safety / advisory information
  • Over height vehicle detection system
  • Weather system
  • Each tunnel accessible to bicyclists
  • Over 600,000 cubic yards of material excavated; 30,000 truck loads.