A track inspector discovered the cracked rail on the outbound tracks between Friendship Heights and Bethesda at 1:10 p.m. Tuesday, according to Metro.
Trains shared the inbound tracks until 4:03 p.m. while temporary repairs were made.
When the rail system is closed Tuesday night, crews will make permanent repairs, according to Metro. The repairs are not expected to affect morning service.
Trains will travel at reduced speeds through the area throughout the day, so riders should expect an additional 15 minutes in delays.
Metro already is advising riders to expect Red Line delays up to 30 minutes throughout the month as the transit agency continues to address track circuit problems at the site of the June 22 collision between the Fort Totten and Takoma stations, which killed nine and injured dozens. Trains have run on manual operation while the issue is addressed.