WASHINGTON — Metro’s Red Line is single tracking in two different places Wednesday because of rail problems, and the transit agency says it will cause big delays for the evening commute.

Red Lines trains are single tracking between Farragut North and Dupont Circle stations because of defective rail fasteners. The defect was detected during a routine track inspection and repairs could take several hours, Metro said in a news release.

Also, Red Line trains are sharing a single track between Medical Center and Grosvenor stations because of a cracked rail. Metro said its working to replace a 39-foot section of rail.

The Red Line’s failed rail fastener comes one day after the same problem near the Smithsonian Station. On Tuesday, the defective rail fasteners caused Blue and Orange line trains to single track through the evening commute.

Both incidents are described as “multiple consecutive defective rail fasteners,” Metro spokesman Dan Stessel said in an email.

Failed fasteners allowed the rails to spread apart and ultimately led to a Blue Line train derailment near the Smithsonian Station in August 2015, which closed several stations downtown for most of a day.

Track inspectors didn’t catch the widening rails. Although specialized equipment detected the problem, the warning was incorrectly deleted from a report and the tracks weren’t fixed. Three Metro employees resigned as a result.