Working all night, Muni and utility crews were able to restore service on the city’s underground subway system in time for Tuesday morning’s commute.

Muni spokesman Paul Rose said normal service was restored at 5 a.m.

All subway trains were shut down Monday evening due to an electrical signaling problem resulting from a blown transformer. The transformer blew near the Van Ness station at about 5:45 p.m. leading to the service outage, Rose said.

The transformer was part of Muni's infrastructure, officials said.

"We know it's not the outside feed from PG&E," Muni Director of Transit John Haley said during the outage. "And we know that the problem is in our hardware that directs the commands to the signals and switches."

PG&E spokeswoman Jana Morris said utility crews did respond to the scene and checked their equipment but did not find a problem. However, they did assist Muni in making repairs.