The lights went out on the lower deck of the Bay Bridge early Wednesday morning, turning the stretch from San Francisco to Oakland into a dark drive for commuters.
The upper portion of the new bridge did not suffer the same problem.
Andy Pacheco tweeted to NBC Bay Area that the lights seemed to be out at 3:30 a.m. when he drove past some leftover flares. "It was a little eerie over the #baybridge this morning," he wrote. "Lights were out over most the western span and the tunnel."
A Caltrans spokesperson said that this has happened before but not since last January, when the western span of the Bay Bridge went dark between Yerba Buena Island and San Francisco temporarily.
Electricians were able to turn the lights back on at 6:20 a.m., but Caltrans crews still don't know what happened.