Operations and maintenance center
The operations and maintenance center, on the south end of the Devil’s Slide tunnels, is manned 24 hours a day and is part of the tunnel emergency plan. It lost power during an outage on Tuesday. Review file photo

State and local government agencies say they are reconsidering their protocols in light of an eight-hour power outage at the Devil’s Slide Tunnels on Tuesday that caused traffic woes for Coastside commuters.

Part of the frustration for many drivers was the lack of information provided by official sources regarding when the tunnels would re-open and what alternative routes were available. Pre-planned tree-trimming work scheduled for that evening on Highway 92 caused traffic to back up onto Interstate 280 and beyond.

Power was restored earlier in the evening and the Devil’s Slide Tunnels re-opened at 12:28 on Wednesday morning, according to Caltrans spokesman Jeff Weiss.

The San Mateo County Office of Emergency Services issued an alert Tuesday afternoon stating the tunnels were closed in both directions and estimated re-opening was 5:45 p.m. No further updates from the alert system were sent out until 9 a.m. Wednesday morning with an update the tunnel was now open for traffic.

County officials were waiting for an update from Caltrans before issuing another alert, according to Detective Rosemerry Blankswade, a spokeswoman for the San Mateo County Sheriff's Office

“We were provided little information and we have to just go off what we get from our stakeholders,” Blankswade said. “This is a learning experience for us on how we work with our partners.”

Caltrans officials say they issued three updates on the state of work at the tunnels, at 6:27 p.m., 8:36 p.m. and 12:24 a.m., according to Weiss. It is unclear who received those updates. The Review did not receive any word from Caltrans overnight.

“We relied on our protocols and did disseminate the information and put up changeable message signs on all the approaches in that area and it was broadcast as well on the major TV and traffic reporting stations,” Weiss said.

Several Coastsiders posted real-time updates on social media. The grassroots effort to spread information filled the void left by a lack of official information.

At about 2:53 p.m. on Tuesday power was reported out near the Devil's Slide Tunnels area causing a back-up power supply to kick in. Traffic through the tunnel was directed by California Highway Patrol officers for about an hour, until the tunnels were indefinitely closed as Caltrans arrived to retest the systems, according to CHP officials.

PG&E reported the outage also affected approximately 4,112 customers in the Pacifica area. “More than half of the customers were restored at approximately 7:19 p.m., and all customers were restored by 8:26 p.m. While the cause is still being investigated, it appears a tree branch came into contact with power lines,” said PG&E spokeswoman Andrea Menniti.

There are three 12 kilo-volt electric lines out to the tunnel from the Pacifica side, which became “unbalanced,” Weiss said. That affected tunnel controls and the jet fans inside the tunnel, according to Weiss. Jet fans are needed inside the tunnel to clear smoke in case of a fire.

“So that is the main concern, for emergency services,” Weiss said.

The tunnels have two sources of power; one from the north side and one that loops around and comes in from the south. If power is cut off before the line splits, it ends up causing the power to go out on both lines, Weiss explained.

With a main artery connecting Pacifica to Half Moon Bay closed on Tuesday, many drivers opted to take Highway 92 to travel home. However, already planned tree-trimming work caused one-way traffic control in the area, which caused further delays.

“Tree-trimming that happened yesterday was an aberration,” Weiss said. Weiss wasn’t sure whether tree-trimmers were alerted to problems on the Coastside’s other main artery.

As for why there is no back-up generator to supply power in case of outages, Weiss explained that tunnel designers went with a more environmentally friendly choice.

“If we used a generator it would be as big as a tractor trailer and use diesel,” Weiss said.

With traffic restored to normal, Caltrans officials are considering what to do if this occurs again.

“This the first time this has happened,” Weiss said. “We will take a look at the operation procedures and review them and debrief on what to do next time.”

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