The first phase starts at 10 p.m. and lasts until March 11, and a second nine-day closure is slated to begin in late April. The closures affect some of the busiest areas for "L" travel in city.
In addition to work on the 90-year-old bridge, the CTA said it will rebuild the tracks above the intersection of Lake and Wells streets, and replace tracks in the curves at Hubbard and Kinzie, north of the Merchandise Mart.
During weekday rush hours, one of every three southbound Brown Line trains will end service at the Merchandise Mart, and the others will travel through the Red Line State Street subway and terminate at Roosevelt.
After 10 p.m. weekdays and on weekends, Brown Line trains will operate between Kimball and Chicago only.
The Purple Line Express will be halted between Howard and Downtown stations during construction, and customers are instructed to use Red Line trains instead.
Various buses and "shuttle trains" will operate to provide Brown Line service and help customers connect to Loop trains, the CTA said. Additional buses will be added on existing routes, the agency said. Some additional Red Line trains should also help relieve headaches.
On weekends during rail work, Brown Line train service will terminate at Chicago and Franklin, while trains on the Green and Pink lines from the west will terminate at Clinton and Lake.
Orange Line trains will terminate at Washington and Wells, and trains will travel only on the Van Buren and Wells sides of the Loop on weekends. Weekend Green Line trains from the south will terminate at Adams and Wabash, and shuttle service will provide travel to Clark and Lake.
The second phase of construction starts about 10 p.m. April 26 and runs through early May 6.
The CTA said working on the bridge and rail construction at the same time is expected to save taxpayers $500,000 in coordination costs. The work is part of the agency's Loop Track Renewal project, which funnels about $33.8 million into renovating more than two miles of "L" track.
Customers are advised to take some extra time and plan ahead before traveling.
Readers can visit the CTA's Wells Street Bridge construction page for full information on the closures.