A problem at a power substation in BART's transbay tube, lead to a temporary shut down and long delays Sunday afternoon.
BART's Linton Johnson said smoke was reported on both sides of the tube just before 2 p.m. For a time, the entire tube was shut down, but by 2:40 p.m. trains were running on one track.
It was not immediately clear what caused the initial problem. Inspectors were called to the scene and were investigating.
"We don't know exactly what it is," Johnson told Bay City News. Johnson said he did not know when the tube would be fully reopened.
Sunday was a wet and rainy day in the Bay Area, but it was not clear if the weather played any role in the problem.