Blue Line trains were back on schedule by mid-morning Wednesday after crews repaired a piece of track that cracked and forced trains to share a track for the first half of the rush hour.

Northbound and southbound trains ran on a single track between the Mall of America and Cedar-Riverside stations for about two hours until the fixes were completed about 7:20 a.m., said Metro Transit spokesman Howie Padilla.

Riders faced big delays on the coldest day of the year, with the temperature around minus-28 and the windchill around 50 below at the time. The arctic conditions were to blame for the steel track's failure on the northbound side near 35th Street.

"In extreme cold, rails contract and can split at weld points," Kerr said. "That's what happened this morning."

That is not uncommon as it happens two to three times a year. Crews put in a temporary fix that will be in place until the weather warms up and the track can be rewelded, Kerr said.

"Commendations to the maintenance engineers who fixed the cracked track in -28°F before dawn," said Sen Scott Dibble, DFL-Minneapolis, in a tweet.

With trains running only on the southbound track, inconvenienced riders were not quite as happy.

"Nothing like waiting an hour and most of it outside for a Blue Line train," said Dan Loomis in a Facebook post.

A few frustrated riders said they were left on platforms with little word about when their trains would arrive. Ashley Powell was waiting at the VA Medical Station for a southbound train to go to Fort Snelling when a northbound train arrived on the southbound tracks. She was told she would have to wait for the northbound train to go downtown before it turned around to pick up southbound passengers.

Rather than "one long wait" in the frigid conditions and unsure of when her train would come, Powell said she got on the trip going downtown around 6 a.m. and rode the train back south after it turned around.

"It's been horrible," she said. "There are no wait times" listed on the boards.

Padilla said the incident is a reminder for to dress appropriately and be prepared for unexpected delays.