SAN FRANCISCO — The Bay Area Rapid Transit District (BART) rail shutdown entered day three as agency officials continued to search for answers as to what is crippling railcars and why the breakdowns are happening, the San Francisco Chronicle reports.

The issue that closed the Pittsburg-Bay Point station began Wednesday when 50 cars had to be taken out of service after they were hit with a power spike as they moved through a track crossover north of the North Concord station.

The surge shot up to 2,000 volts of power through some of the car’s vital components — twice what BART expects for normal operations — and the agency isn’t sure exactly why the issue has emerged.

The surge caused a semiconductor device called a thyristor to fail. BART said the parts — which are critical to each car’s propulsion system — cost $1,000 apiece, are difficult to acquire and could take months to replace. For the full story, click here.