Westbound traffic through the Caldecott Tunnel on the Orinda side was backed up Monday morning because of a power outage, a Caltrans spokeswoman said.
Construction crews were attempting to transfer power from bores 1, 2, and 3 around 1 a.m. to a new substation that is opening as part of a system for the new fourth bore, spokeswoman Ivy Morrison said.
As part of the transfer, the older electrical system is being integrated with the newer one, and in the process it tripped the circuit breaker, she said.
This caused an electrical outage, which affected the traffic "pop-ups" that switch between lanes to direct motorists to the tunnels that are open.
Because there was no electricity, the poles that block or open the roadway were stuck and only one bore was accessible for westbound traffic this morning, Morrison said.
Usually two bores are opened for the heavier westbound direction in the morning.
Morrison said contingency power sources are in place and all equipment is working at the tunnel for the afternoon commute.
"We are very sorry for the inconvenience," she said.
The fourth bore is expected to open by December, Morrison said.
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