A Metro mechanic was in critical condition Tuesday after he was struck by a slow-moving train in a maintenance yard near the Shady Grove station.

Transit agency officials would not release the man’s name but said he has worked for the agency for 28 years.

He was hit shortly before 1 p.m., when a four-car train was near where trains are washed at the rail yard. He ended up under the first car, Dan Stessel, Metro’s chief spokesman, said. Rescue workers had to lift the train and cut pieces of the track to extricate the man, which took nearly an hour, said Assistant Fire Chief Scott Graham of Montgomery County’s Fire and Rescue Service.

“He was conscious during our extrication and cooperative,” Graham said. The man was taken to Maryland Shock Trauma Center in Baltimore.

Rail service was not affected.

Metro said the incident was being investigated and that safety practices at the rail yard were being reviewed. Employees were also being offered counseling. The National Transportation Safety Board and the Tri-State Oversight Committee were notified of the incident, according to Stessel.

Jackie Jeter, president of Local 689 — the union that represents a large portion of Metro’s workers — said she had been told that the man had “lost part of his leg.”

Metro has had incidents of workers dying after being hit. In 2010, two track workers were hit and killed by equipment near the Rockville station. In 2009, two workers were fatally struck: one near the Dunn Loring stop, the other at Reagan National Airport.

Watchdogs have been pushing for federal safety standards for Metro and other transit agencies because of growing concern about workers and riders. There is no national oversight or setting of standards for subway safety.