Twenty-two BART cars break down suddenly on a stretch of track between the North Concord and Pittsburg-Bay Point stations.
That was the scenario last Friday. And if it sounds familiar, it’s because a little more than a year ago, about 50 BART cars were knocked out of service by mystifying electrical spikes that occurred in the same area.
BART said Monday that its engineers have concluded that Friday’s incident is similar to the one that occurred last year: Electricity jumped from the third rail and fried equipment on the cars.
BART spokesperson Jim Allison said that section of track is especially prone to electrical surges. The trains there draw a lot of power to get over Willow Pass.
Allison says the third rail there approaches 1,250 volts, “near the high end” of BART’s acceptable range of voltage.
Engineers believe that the power surges seen Friday were made more likely by metallic dust on the tracks.
“This metallic dust basically creates a pathway for the electricity to jump,” Allison said. “And when it does that, it damages the semiconductor parts on the underside of the cars.”
The dust was left behind by recent rail-grinding.
“In the last three weeks we’ve been grinding between North Concord and Pittsburg stations four nights a week,” says Allison. “So what we’re surmising is that this buildup of the dust there, and combined with the extra juice that they were getting from the third rail, that’s what created the problems on Friday.”
In response, BART has turned down the power. Allison says that since Friday night, that stretch of track has gotten 5 percent less voltage than before. He says that the speed of service has not been affected.
BART is taking another measure to reduce the risk of surprise electrical spikes. The agency is ordering a pair of giant magnets to attach to maintenance vehicles.
Now, when crews go out to grind and smooth the rails, the magnets will attract the resulting metallic dust.