CTA journeys are about to get more arduous for commuters heading to the Illinois Medical District, students heading to UIC and travelers connecting to Amtrak at Union Station.

CTA Blue Line tracks between the West Loop and the Illinois Medical District are set to temporarily close this summer, as work gets underway to remove some of the slow zones that plague the Forest Park branch of the line.

The Clinton, UIC-Halsted and Racine stations will close in stages from late July through early October. During the closures, the CTA will undertake a $268 million project to rebuild the track and upgrade the power system. The agency will also begin to completely rebuild the Racine station, which will continue into the coming years.

The CTA will run shuttles during the closures and is offering incentives to encourage riders to take alternate train lines. Still, the closures will mean longer commutes for Blue Line riders.

The effects could also be felt up the busy O’Hare branch of the Blue Line, CTA spokesman Brian Steele said. With part of the line out of service, wait times along the rest of the line could be a “couple of minutes” longer. But when work is finished, fewer slow zones along the Forest Park branch should also mean better service along the entire line, the CTA said.

Work is tentatively scheduled to begin July 23, and the closures will take place in two phases. For the first roughly 30 days, trains will not run between LaSalle and the Illinois Medical District, and the three stations in between will be closed.

From late August until roughly Oct. 7, the track closure will shorten to between UIC-Halsted and the Illinois Medical District, and only the Racine station will remain closed.

The CTA will run shuttles at all hours, every day, stopping at every closed station. During the first phase of work, the shuttle will run between the Illinois Medical District and Jackson, because, although the closure only extends to LaSalle, Jackson is compliant with the Americans with Disabilities Act.

The agency is encouraging riders to consider alternate service, like the Green and Pink lines, during the closures. The agency will be offering discounted fares on the lines, though the exact discount has not yet been determined, Steele said. Bus rides on routes between the Pink and Green lines will be free for riders who board in the construction area.

During the first stretch of work, when three stations are closed, the CTA will also run an express shuttle during peak morning and evening commuting times that will stop only at the Illinois Medical District and Jackson.

“We want to keep people on the CTA system during this work,” Steele said. “And even though some commutes — in fact let’s go ahead and say most commutes — through this area are going to take longer, the CTA will still be the most affordable, the most convenient, and, given some of the traffic congestion we’ve been seeing in the region, it will still be competitive in terms of travel time.”

The Forest Park branch of the Blue Line, which runs down the center of the Eisenhower Expressway, opened in 1958. It’s the only section of track that hasn’t had major improvements to it since it was constructed, according to the. CTA.

About 80% of the 17.8-mile branch has slow zones, which force trains to crawl down the highway median and add time onto riders’ commutes. Work between LaSalle and the Illinois Medical District will remove three miles of slow zones.

The work on the eastern edge of the branch, funded by state money, CTA bonds and funding from a city tax increment financing district, is intended to be the first stage of a complete rebuild of the line. No funding or timeline has been identified for work on the remaining pieces of track, the CTA said.

Once the tracks have reopened, parts of the Racine station will remain closed while the station is demolished and rebuilt. Rebuilding the main portion of the station is expected to take place through 2024, and after that the main entrance will reopen and work will move to an auxiliary entrance.

Trains will continue to stop at Racine during the station construction.

Steele said the Blue Line project is a major investment in Chicago’s West Side, and an effort to strengthen and better connect communities.

“The Forest Park Branch of the Blue Line is a critical transit asset for Chicago’s West Side communities, directly serving the Illinois Medical District, several schools and colleges, as well as several other growing employment centers,” CTA President Dorval Carter said in a statement. “The start of this project work is long overdue, and the CTA is committed to securing the additional funding to advance future phases of work to provide all Blue Line riders a better transit experience.”

sfreishtat@chicagotribune.com