Metra urged commuters going home via Union Station to consider alternate routes with switching problems creating delays of up to an hour Thursday afternoon.
Trains are unable to leave or arrive at the Chicago hub "for the time being" a message posted shortly before 5 p.m. notified riders.
The messup, occurring at the height of rush hour, has created crowds at the downtown station and the commuter railroad recommended passengers wait for 30 minutes before boarding trains.
"Metra and the Burlington Northern Santa Fe strongly suggest commuters to consider using the Union Pacific West Line or any other alternate means of transportation," the railroad said in an alert.
Amtrak is working to fix the problem, officials said.