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A problem with signal cables being torn by sander hoses on the trains is one reason for all the recent Muni Metro delays.

Updated Jan. 19, 2011, 11:13 a.m.

Underground San Francisco Municipal Railway service has resumed after being halted early this morning by a car that drove into the tunnel near Church and Duboce streets and got stuck, a Muni spokesman said.

"The car is cleared off of the tracks, but it will remain in the subway throughout service the rest of the day," Muni spokesman Paul Rose said.

He said the car would be removed once service ends tonight.

Normal Muni service resumed at 8:18 a.m., Rose said.

During the disruption, street-level shuttles were used to transport Muni passengers instead of the underground light rail.

Service is a little slow, however, because the car damaged a switch on the tracks, and trains have to pass over it at reduced speeds, he said. Muni workers will have to wait until tonight to make repairs to the damaged switch.

Police are still investigating the incident.