BART trains began running again tonight between Hayward and Fremont, service that was unable to open this morning because of a power substation fire.

The 4:26 a.m. fire broke out a BART train yard power substation where crews were upgrading equipment. Human error may have caused the fire, although more needs to be known to pin that down, said BART spokesman Linton Johnson.

The fire, along with a second blaze at the same substation later in the morning, caused millions of dollars to an adjacent BART tower with senstive high-tech equipment for tracking trains, Johnson said.

BART had been running buses all day to shuttle passengers between four stations, Hayward, South Hayward, Union City and Fremont. Trains begain running again about 8:30 p.m., although some trains were delayed about 10 minutes.

Train service was not affected elsewhere in the four-county BART system. However, Johnson said it appears doubtful that BART will be able to run longer trains tonight as planned to ferry passengers to the KFOG KaBoom fireworks show along the Embarcadero in San Francisco.

BART has had a difficult time moving the extra cars needed for bigger trains. The cars are stored in the Hayward train yard, which has been without power. BART crews this afternoon were manually pushing the cars out of the yard, Johnson said.

"This is the worst electrical incident in BART's 35 year history," Johnson said, adding he did not know how long it would

take to repair the BART tower and regain full use of the train yard.