Metro general manager and chief executive officer Paul Wiedefeld announced he would be retiring effective immediately Monday after the Metro announced delays due to a failure to recertify train operators.

The Washington Metropolitan Area Transit Authority announced Sunday that Yellow and Green Line trains will be running on a delayed schedule because “nearly half” of its rail operators were not up to date with their certifications. Wiedefeld, who announced in January that he would be retiring later this summer, said in his statement that he is retiring now to make interim General Manager Andy Off’s transition into the position smoother.

“I believe conveying all authority of the General Manager’s office to Mr. Off better positions him to address the challenges that came to light this week, while preparing for the transition to the next CEO,” Wiedefeld said.

WMATA’s Board of Directors selected Randy Clarke to be the Metro’s next permanent general manager and CEO earlier this month, according to a release.

The new delays come after the Metro’s 7000-series trains were pulled from the tracks in October after a Blue Line derailment. 7000-series railcars still haven’t returned to service, causing severe service delays.

Joe Leader, Metro’s chief operating officer, also resigned effective Monday. Wiedefeld thanked Leader for “his tireless work and dedication” to the position in his statement.

“Stepping aside a few weeks ahead of schedule is in the best interest of the agency and its workforce, whom I have been deeply proud to lead over the last six years,” Wiedefeld said.