NORTH CONCORD (CBS SF) — BART train service is gradually returning to a route between two East Bay stations that was beset by an electrical issue that damaged train cars a week ago.

Two shuttle trains will be deployed at 3 p.m. Wednesday to take riders between the Pittsburg/Bay Point and North Concord/Martinez stations and one train will continue to be used after 8 p.m., BART officials said.

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Train service between the stations had been suspended until Monday, when BART officials announced one shuttle train would return limited service to the line during morning and evening commute hours.

Buses were taking BART riders between the stations outside of those hours while crews investigated an electrical issue first reported around 10 a.m. on March 16.

Buses are still being used Wednesday until 3 p.m., when an additional train is being introduced to the initial one-train plan, which is expected to reduce the time between trains arriving from about 15 minutes to 10 minutes, BART officials said.

Train service was originally restarted between the stations after a test train carrying riders made multiple successful trips starting Sunday night.

The test train was assessing a voltage spike train cars had been experiencing while passing between the stations, damaging the cars’ propulsion systems.

Although the problem was not dangerous for riders, a portion of the more than 50 train cars damaged by it will require a lengthy and expensive repair.

Some train cars need to have a part replaced that is typically only received every 22 weeks from a specialized manufacturer, BART chief mechanical officer Dave Hardt said at a news conference last week.

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As a result, he expected it to take months for BART’s fleet to be recovered fully. He also expected that buying all the particular parts could cost up to an estimated $100,000.

BART officials said alternate suppliers of the spare parts needed are also being explored.

Systemwide, trains may have less cars and may be more crowded because of the diminished number of train cars available in BART’s fleet. BART officials have apologized for the inconvenience this problem has caused riders.

BART spokesman Jim Allison said agency employees were at the North Concord/Martinez station on Tuesday offering free passes to riders and were handing snacks out to those using the buses at that station Friday afternoon.

BART spokeswoman Alicia Trost said the agency was “cautiously optimistic that the car availability will be on an upward trajectory toward improvement.”

Trost added that the amount of available cars in the fleet did improve over the weekend by 36.

While one crew continues working to repair the remaining out-of-commission train cars, another is investigating the cause of the voltage spike, which BART officials said has still not been determined.

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Outside expertise has been recruited to help with the troubleshooting, BART officials said.