Riders should listen for announcements at the stations.
Metro-North said the delays would continue until further notice.
After an overnight test opening of the track 1 and 3 span, the Devon Movable Bridge became stuck in the open position, Metro-North said.
The remaining two tracks are operating at reduced speed through the area.
Workers with Metro-North and the Connecticut Department of Transportation are on the scene assessing the situation.
The 110-year-old Devon Bridge is undergoing a six-month, $5.8 million repair project. The work involves steel repairs, a new wooden deck and new miter rails on the Track 3 span. The bridge carries Metro-North and Amtrak trains over the Housatonic River.
The four-track Devon bridge is slated to be replaced in the future. It is one of several moveable bridges on the New Haven Line that are more than a century old. The others include the Mianus River Railroad Bridge in Cos Cob, built in 1904; the Norwalk River (WALK) Railroad Bridge in Norwalk, built in 1896; the Saugatuck River Railroad Bridge in Westport, built in 1905; and the Pequonnock River Railroad Bridge in Bridgeport, built in 1902.
Click here to follow Daily Voice Bridgeport and receive free news updates.