Metro says the 7000-series trains will return to service gradually instead of all at the same time, once approved to do so by the Washington Metrorail Safety Commission.

When that may happen is still unclear, though. During Thursday’s Metro board meeting, General Manager Paul Wiedefeld said “we hope to know more about the timing of the return before the Christmas holiday, but all steps in the process must be satisfied to proceed.”

Those steps include Safety Commission approval of Metro’s increased testing plan, which would measure wheel spacing every eight days instead of every 90 days. An October derailment on the Blue Line was caused partially by one set of wheels moving two inches further apart on an axle. If wheels move more than 1/16th of an inch, cars are supposed to be removed from service.

The Metrorail Safety Commission pulled the trains from service in October until Metro could identify what was causing the issue and come up with a corrective plan. The Safety Commission didn’t have any additional comments Thursday.

Metro hopes the increased inspection will catch any issues and prevent another derailment. The transit agency has been testing its hypothesis. For two weeks in November, it ran two 7000-series trains under simulated passenger service conditions to establish the correct, data-driven inspection interval for these railcars, Metro says.

“While the test period has ended, Metro’s Safety Department and Railcar Maintenance engineers are busy reviewing the data and incorporating observations from the test period into a final inspection plan,” Metro said on Twitter Thursday. “The proposed plan will include more frequent wheelset inspections, which must be reviewed and accepted by the WMSC before the 7ks can return to service.”

While reduced service will be here until at least the end of the year, Metro says it’s planning for incremental service improvements as the newer trains are phased in. Train arrivals would increase to every 8 minutes on the Red Line (better than the current 12-minute intervals) and 15 minutes on all other lines (better than the current 20-minute intervals on Yellow and Green lines and 24-minute intervals on Orange, Blue, and Silver lines). Metro is still charging peak fare, which is chafing many riders as they wait on the platform longer and have more crowded trains amidst the ongoing pandemic.

Metro says service isn’t adding in all at once; rather, the plan is to swap out the older trains with the approved 7000-series trains as some of the older trains have intermittent reliability problems with things like doors and brakes. Metro says this will provide a “better overall customer experience and help reduce the number of railcar-related delays.”

Metro knew of the 7000-series train car wheel issues as far back as 2017 and the issue got progressively worse. Metro told the National Transportation Safety Board it found 20 instances of wheels out of alignment during a fleetwide check after the derailment.