Lights on the eastern span of the Bay Bridge were spotted late Wednesday flashing on and off.
The odd sight left motorists and many on social media seeking answers. A Caltrans spokesperson said technicians are responding to the bridge to investigate the flashing lights, but said traffic is not affected.
Caltrans said it believes it was an electrical issue with a short circuit at a substation on the bridge.
An agency spokesman said it could have been weather related because it was raining heavily at the time the flickering started.
No other information was immediately available.