Work crews will be replacing ties and other infrastructure along the Red and Blue Lines, officials said Monday. They will also be completing work on the on-going Brown Line expansion project, official said.

On the Red Line, until 4 a.m. today, a single track was expected to be available for all southbound trains, officials said. The work began at 11 p.m. Monday.

At the North/Clybourn station, southbound customers will need to board and exit trains from the northbound platform, officials said. CTA operators will announce the direction of each train.

There will also be significant rerouting along the late night Red Line through Friday morning between the Cermak-Chinatown and Fullerton stops. Northbound service will be temporarily rerouted today and Wednesday from 9 p.m. until 5 a.m. the following morning. The same reroutes will affect southbound travelers on Thursday from 9 p.m. until 5 a.m. the following morning.

During the rerouting, the Red Line train will deviate from its traditional path, stopping only at the following locations between Cermak-Chinatown and Fullerton: Roosevelt/Wabash, Adams/Wabash, Madison/Wabash, Randolph/Wabash, State/Lake, Clark/Lake, Merchandise Mart, Chicago/Franklin, Sedgwick and Armitage.

The CTA is advising riders who don't typically use the Merchandise Mart station that it is exit-only from 1 a.m. to 5 a.m.

Also beginning today, late night Blue Line riders should also allow extra travel time this week as crews work in slow zones from 8 p.m. each night until 4 a.m. the following morning, officials said. A single track will be in effect for northbound Blue Line trains between the Montrose and Addison stations.

Customers boarding and exiting at the Irving Park station must do so from the southbound side of the platform. The late night single track slow-down will be in effect through Friday morning, CTA officials said.

The northbound Brown Line trains will also operate with a single track between the Addison and Western stations from 8 p.m. each night until 4 a.m. through Friday morning. Northbound customers at the Montrose Brown Line station must board and exit trains from the southbound platform.

Red and Brown Line trains will also be temporarily rerouted at Fullerton Thursday night. That reroute will last from 9 p.m. until 4 a.m. Friday. During that time, southbound riders must board and exit trains from the northbound Red Line side of the platform. Southbound Brown Line trains, meanwhile, will be unable to stop at Diversey. The CTA is advising southbound Brown Line customers who usually exit at Diversey to exit at Fullerton instead and board a northbound train to their stop. Customers boarding at Diversey traveling southbound should board a northbound train and exit at Belmont to board a southbound train.

The #77 Belmont bus will also be rerouted this week. For more, go to CTA's website.