A Red Line train operator used his emergency brakes fearing he might have been too close to another train, according to Metro.
The transit agency is not calling it a near collision, but Metro hasn't said how close the trains got.
Operators rarely hit the emergency brakes.
The operator reported using the emergency brake at 1 p.m. Wednesday, although the incident actually happened at 9 a.m. between the Forest Glen and Wheaton stations. As he pulled into the Forest Glen station, he applied the brake because he feared he might be too close to another Glenmont-bound train stopped at the station.
Both trains were carrying passengers, but no one was hurt.
Investigators are downloading data from the trains to figure out how close they did get.
Metro trains have been operated in manual mode since one Red Line train plowed into another stopped on the tracks killing nine people last June. Wednesday's incident shows why it's important to operate in manual mode, said Metro spokeswoman Angela Gates.