Metro bus operators think a pair of master switch failures caused buses to stall without warning, leaving drivers unable to steer or stop the bus.

“This is a really big deal,” said Anthony Garland, a former bus operator who now represents members of Amalgamated Transit Union Local 689.

Garland fears thousands of riders could have unknowingly taken rides on 8000-series buses between the first incident September 25 and when 105 of the buses were “voluntarily parked” by WMATA after the second such incident September 28.

Garland said in the first incident, the driver of a bus on I-395 in Northern Virginia hit a median barrier at 60 miles per hour when the bus suddenly lost power. WMATA says the bus was taken to a facility in Landover for further inspection.

E-mails obtained by WUSA9 show that a maintenance superintendent warned other superintendents the following day that there were issues with the newly installed master switches.

“At the time the email was sent, the concern had not been substantiated, and the superintendent had no knowledge of the investigation,” said a Metro spokesperson.

After the second incident in Fort Washington last Thursday, a Metro spokesperson says the agency responded within 90 minutes, parking the buses until an investigation could be finished.

“It has since been determined that, while the cause of the second incident may be related to a mis-wired switch, it was not related to the concern raised in the September 26 email which, again, would not have resulted in a bus stalling,” a Metro spokesperson said.

Still, Metro bus operators say they needed to know of possible problems first.

“That’s not how you build a safety culture,” said Garland.