Blue Line trains were back on track just in time for Monday's morning commute as crews finished making emergency repairs to overhead wires and a pole damaged in a freak derailment over the weekend in Bloomington.

Service between the Mall of America and the Humphrey Terminal at the Minneapolis-St. Paul International Airport stopped Saturday afternoon and resumed at 5:04 a.m., just as commuters were arriving at two of the busiest stations affected by the shutdown.

Buses were at the ready to fill in if the repairs had not been completed, said Metro Transit spokesman Drew Kerr.

A northbound train struck a loose switch plate cover around noon Saturday and jumped the tracks between 28th Avenue and Bloomington Central stations. The wayward piece of metal got caught in the wheels of the front car. That caused the train to go off the tracks and strike the concrete foundation of a pole holding the overhead electrical wires. None of the 60 passengers nor the train operator were injured, Kerr said.

The derailment was unusual in that it was the first caused by a mechanical problem, Kerr said. It was the second derailment in the Blue Line's 10-year history. The first, in downtown Minneapolis in March 2011, was weather-related.

After the damaged pole and wires were reset, Metro Transit ran test trains through the area before resuming regular service. Buses had been filling in during the disruption, including two northbound trips between 4 and 5 a.m. Monday.

"We were grateful that we were able to start trains before the rush hour," Kerr said. "Customers would have been inconvenienced. Buses are never the same as trains, but we were ready to go."

Tim Harlow • 612-673-7768