The mysterious glitch that knocked 50 BART cars out of service one morning in March, causing service issues and delays throughout the system for weeks, has disappeared as quickly as it appeared as CBS 5 reports. Still, because they never actually got to the root of the voltage spikes — which occurred in two different places in the system and seemed to effect one particular type of older train car more than others — BART Assistant General Manager Paul Oversier told the agency's Board Friday "we need to get to the bottom of it," and cautioned that it could return.

It's a strange situation, and one that isn't particularly reassuring for commuters, despite the fact that normal train service resumed two weeks ago, and that the problem appears to have gone away, for now.

As BART explained in this release Friday, it was the fleet's C cars that were most prone to damage, and one of the first fixes to the issue was to rotate these cars off of the Pittsburg/Bay Point line, where the voltage surges were occurring and damaging essential propulsion parts of these trains.

But, now they've started rotating C cars back onto this line with no apparent trouble.

Oversier says, "We don't want our customers to suffer through another round of this so we need to get to the root cause."

BART has hired outside experts, including electrical engineers and now some new "process experts on problem-solving," who are all working to figure out the issue. Another theory being floated now, says Oversier, is "ionized air." "If you have ionized air, it could be a possible source of the arcing we were seeing," he says. "So, we have been doing air sampling alongside of a moving train to see if there is ionized air."

The current trouble began on March 16 when voltage spikes occurring between Pittsburg/Bay Point station and North Concord station took those 50 cars out of service. This was preceded by a similar though less severe problem near the Transbay Tube several weeks earlier that also knocked some cars out of service.

BART says the car count is coming back up closer to the normal service fleet of 579 cars, though it's unclear right now what that exact count is. (The infographic shown here is way out of date.) As we learned the other week, in order to repair some of the 40-year-old train cars, BART engineers have had to scrounge for obsolete parts on eBay. They had previously said that manufacturing and shipping replacement parts was going to take months.

Previously: After Weeks-Long Electrical Problem, BART Nearing Regular Service
BART's Actually Gotten More Reliable Over Last Seven Years, Not Less — Are They Just Crying Poverty?