Updated Saturday, 11:20 a.m.
BART has returned to normal service systemwide after a computer error shut down the transit service for hours Saturday morning.
BART Back Open After Computer Error Shuts System Down for Hours
According to BART, the system experienced a "computer network failure" overnight, which prevented BART from turning on the system that routes trains and delaying the beginning of Saturday service by more than three hours and the restoration of full service by nearly five hours.
The transit agency originally announced that overnight work on its emergency power supply system had unexpectedly impacted its traction power and train control systems, but later determined that the work was not connected to the outage.
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"BART will perform a complete forensic evaluation to determine exactly what happened," the transit agency said in a statement. "This analysis is expect to take several days due to the complexities of our system."
Limited service resumed at 9:09 a.m., but full service was not restored until just before 11 a.m. when trains began running between Daly City, Millbrae and San Francisco International Airport.
Bus agencies including Muni and SamTrans offered mutual aid service from BART stations during the outage.