Feature Story

Famed California Tunnels Combine Technology with Beauty

by Mary Gorges

The Devil's Slide Tunnels make a dangerous stretch of Highway 1 along California's scenic coast a whole lot safer for drivers …with some help from technology including sensors and cameras.

The Devil's Slide area just south of San Francisco has seen its share of drama – quite literally. This incredibly scenic stretch of Highway 1 was featured in the 1960 movie thriller "Portrait in Black" about a couple who drives a car carrying the woman's dead husband off a cliff.

Scene from Portrait in Black

White-knuckled drivers

In real life, drivers here were about as white-knuckled as actors Lana Turner and Anthony Quinn …at least before the two Devil's Slide Tunnels opened in March of 2013. The area was famous in its own right for numerous landslides and car crashes over the past 80 years, some blamed on drivers looking at the views – instead of the road.

Integrated Tunnel Management System

South tunnel entrance

The 1.3-mile long tunnels were bored into the hillside to bypass the most dangerous stretch of the road, and filled with sensors, cameras and other equipment to make the route safer. Ed Der, a construction engineer who managed the project for Caltrans, says all devices are connected over a fiber optic network and managed by a SCADA (Supervisory Control and Data Acquisition) System, with data from the devices monitored 24/7 on screens in a nearby Operations and Maintenance Center (OMC).

Technology you can see

Video from just outside a tunnel entrance

Closed circuit video cameras are installed all along the inside of the tunnel and connected to sensors that detect traffic or dangerous levels of nitrogen oxides and carbon monoxide. Der says if someone uses a call box phone in the tunnel, cameras will automatically turn to view the call box, and feed video and images back to the OMC. Everything is seen in real time on computer screens, and monitored by actual people.

Two fans on the ceiling of one tunnel

Fans in the tunnel (8 pairs in each) go on automatically if sensors detect smoke or high levels of gases. Says Der, "During the parade of antique cars during the tunnel's opening celebration, the buildup of carbon monoxide from the idling cars waiting to exit the tunnel set off the jet fans".

A linear heat detector wire can also be spotted if you look up while driving through.  Shawn Murphy is a senior project manager with Bleyco, which installed all the electrical equipment. He says fans will start automatically if data from the heat detectors indicate the temperature has reached 190 degrees. "Phone calls will go out to the fire and police department, and signage will go on automatically that says ‘tunnel closed'," says Murphy.

What you can't see

‘Loop detectors' are buried in the concrete roadway of the tunnel and send real-time data to the network system. Murphy says these sense the vehicles moving over them, and will even count the vehicles, and automatically detect if there's a traffic jam. The SCADA system will recognize the abnormality and alert the system operator. "And if all of a sudden, there are cars going over some and not others, we'll question, ‘why hasn't this car made it past this point?' And the sensors will send an alert to the computer screens," says Murphy.

Section of Hwy 1 bypassed by tunnels now part of CA Coastal Trail

Der says a lot of the decisions in building the tunnels were driven by aesthetics as the area is so scenic. Even rock at the entrances was made to match the environment. But these same scenic hills can sometimes cause wireless signals to drop so the devices are all hard wired behind the concrete tunnel walls.

Ed Der, Caltrans Construction Manager
"If we had put in a dish antennae, we'd have ruined the aesthetics. Because we're along such a scenic coastline, we wanted to blend in with the beauty. It's all about the aesthetics." Ed Der, Caltrans Construction Manager