The big test for CTA Brown and Purple Line commuters starts Monday, with the closure of the Wells Street Bridge.
The south end of the 90-year-old bridge over the Chicago River is being replaced over the next week for both cars and CTA tracks.
Shuttle buses will take commuters from the Chicago Avenue stop and Merchandise Mart into the Loop and back.
Signs are posted for CTA riders, and detours are in place for vehicles.
On Sunday, Mayor Emanuel joined transportation officials to explain how crews will replace the old with the new in a short period of time.
“It’s going to be an inconvenience,” Emanuel said as workers dismantling part of the bridge toiled behind him. “You can’t spin your way out of that. It is going to be an inconvenience. On the other hand, of the nine days, four out of the nine are on the weekend, when there’s less commuter business traffic.”
The south end of the bridge will be completed by next Sunday.
The process will be repeated for the north end between April 26 and May 5.