Delays on the Metrorail will last for at least three more months to give Metro officials more time to investigate the cause of earlier derailments before the agency’s 7000-series railcars return to the tracks.

Washington Metropolitan Area Transit Authority officials said Thursday that the agency will postpone the return of the railcars, which account for more than half its fleet, for about 90 days until they determine the root cause of wheel issues that caused a Blue Line derailment in October. The release states officials will also “acquire technology” that will allow WMATA to quickly measure and analyze wheelsets to identify potential problems in the future.

“We are going to redirect our efforts toward identifying and tackling the root cause of the derailment and take steps to better support more continuous wheel measurements by installing trackbed technology,” Metro General Manager and CEO Paul Wiedefeld said in the release.

The extended delays serve as another blow to WMATA’s efforts to bring back the railcar series, which officials removed from service in mid-October following the derailment near Arlington National Cemetery. Metro officials said at the time the axle assembly on the derailed train was “out of compliance” with safety standards, and investigators found similar defects on several other railcars not involved in the derailment.

The issues have remained unresolved, leading to Metro’s now six-month stretch of reduced service that has set back arrival times with up to 15- to 30-minute waits for local commuters.

WMATA started returning the 7000-series trains to service in mid-December but halted out of an abundance of caution two weeks later.

“Our customers are always top of mind and none of the decisions we’ve made are easy, but they are critical to our ability to restore service,” Wiedefeld said. “We appreciate each and every customer who continues to ride Metro and recognize that many people depend on the service.”