CHICAGO (AP) — Electric-powered commuter trains in the Chicago area are getting back to normal operations after Arctic cold played havoc with overhead powerlines and forced the shutdown of two major lines.

The South Shore Line , which runs into northern Indiana, and some Metra Electric Line trains resumed Sunday after four days without service. The Metra Electric Line was also impacted by a Wednesday freight train derailment that damaged power supplies.

Temperatures that plunged last week messed up connections between the powerlines and cables that feed power to locomotives. Even as temperatures rose Friday, crews still needed time to get the system into working order.

Metra was resuming service on the entire Metra Electric Line on Monday, but trains will run on a modified weekday schedule due to repairs of the derailment damage.