Amtrak passengers traveling between St. Paul and Minot in far northwest North Dakota can board again after five days of disrupted service, but North Dakota promises to cause passengers headaches throughout the summer.

Passenger train service between St. Paul and Minot was unexpectedly suspended for parts of five days until Thursday because of the aftereffects of a severely cold winter, Amtrak spokesman Marc Magliari said.

But work will continue into September on tracks in North Dakota, forcing westward passengers onto buses in Fargo, Grand Forks, Devils Lake and Rugby through to Minot.

The five-day disruption was the latest problem on the Empire Builder route, which runs from Chicago, through Wisconsin, Minnesota, North Dakota, Montana, Idaho and ends in the Pacific Northwest. Passengers have faced long and chronic delays throughout the last several months.

Eastbound service on the Empire Builder from Minot to St. Paul was suspended starting Saturday and resumed Wednesday, while westbound trains between the two stations were halted Sunday and resumed Thursday.

The service suspension came just weeks after Amtrak’s ballyhooed return to the historic Union Depot in downtown St. Paul after a 43-year absence. The depot recently finished a $243 million face-lift.

“Certainly, it is a challenge for the customers of Amtrak,” said Deborah Carter McCoy, spokeswoman for the Ramsey County Regional Railroad Authority.

Magliari said the interruption was needed to allow for maintenance on the tracks, which are owned by the freight carrier BNSF, because of “this awful winter, this awful spring and the temperatures swings a week or so ago that were forcing all this water up and out of the ground and onto their railroad.”

Repair crews “got a lot of work done that otherwise wouldn’t be done” without the service suspension, Magliari said. Crews “were seeing things they’ve never seen before, like mud boils,” as the water surged from below.

Much of the trouble also has been pinned on heavy freight traffic because of the North Dakota oil boom, an overall improving economy and severe winter conditions straining track equipment.

In mid-December, Amtrak canceled five runs of the Empire Builder between St. Paul and Spokane, Wash., citing lengthy delays for hundreds of passengers attributed to the freight traffic. The cancellations were an attempt to get the schedule “back on cycle,” Amtrak said at the time.

In mid-April, Amtrak adjusted its Empire Builder schedule in hopes of giving passengers a better chance to arrive on time amid the chronic congestion.

BNSF has said its recovery plan includes investing $1 billion in 2014 to improve and expand rail capacity in states along the Northern Corridor, which spans from the Pacific Northwest to Chicago.

“Those investments will benefit Amtrak and all of our freight customers, and many of those projects are already underway,” BNSF spokeswoman Amy McBeth said. That includes the summer disruptions in North Dakota. BNSF will pick up the bus bill.