SAN FRANCISCO (CBS SF) — BART is fixing a mysterious power surge problem in the Transbay Tube that’s resulted in fewer and more crowded trains but hasn’t yet figured out the root cause of the problem, a spokesman for the transit agency said Friday.

BART spokesman Jim Allison said BART has had intermittent problems with train cars being knocked out of service while going through the tube, which runs under the Bay and connects the East Bay with San Francisco, but the problem became more frequent starting on Feb. 20 and reached the “watershed” stage on Monday.

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Allison said, “We’ve seen a decrease in the number of propulsion failures since we changed our power supply configuration” on Thursday and he expects that number to “dramatically decrease this weekend and next week.”

However, Allison said BART crews “will go out again tonight to try to pinpoint why this is occurring and look at it in more detail.”

BART’s goal is to have 62 trains running at full 10-car length during peak commuting hours but 18 trains ran short on Thursday and 17 trains ran short during the morning commute Friday, Allison said.

“That’s not anywhere close to where we want to be,” Allison said.

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BART hopes to be back to its normal train car count by Monday but it might take a while before there’s a permanent solution to the problem, he said.

When train cars get knocked out of service they have to be towed to repair yards at the end of BART lines, according to Allison.

The transit agency then has to run shorter trains, which can carry fewer passengers, he said.

The problem is coming at a bad time for BART because in February it set an all-time ridership record by averaging 446,650 on weekdays, Allison said.

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