In a move to alleviate crowding on the increasingly packed Blue Line, the Chicago Transit Authority is starting work on a $207 million project to replace the 35-year-old signal system along the 16 miles of track between the Jefferson Park and O’Hare stations on the city’s Northwest Side.

The work represents the first significant upgrade to this section of the Blue Line since it was extended from Jefferson Park to O’Hare in the early 1980s, according to the CTA. The project will provide more reliable service and, more importantly, allow the CTA to add more trains to meet swelling demand.

Before transit riders can reap the benefits of the improvements, the CTA says they will need to endure seven weekend-only and two extended service disruptions between now and November. The first is scheduled for this weekend—10 p.m. Friday, May 3 through 4 a.m. Monday, May 6—and will affect service between the Jefferson Park and Harlem stations.

Although the CTA will provide free regular shuttle service between the stations and a complimentary transfer for Ventra users, the disruption will certainly complicate plans for weekend travelers headed to and from O’Hare International Airport. The next service interruption was scheduled for the weekend of May 17, but has been cancelled according to the CTA.

The Northwest Side signal modernization is the latest phase of the CTA’s larger $492 million Your Blue Line modernization program, announced in 2013. It includes track improvements and the overhaul of 14 stations, nine of which have already been completed.

Last fall, the CTA brought extra rush hour trains to the busy O’Hare branch of the Blue Line and rolled out newer cars with additional standing room to boost passenger capacity. The agency is also in the process of upgrading three electrical substations along the O’Hare branch so that it can add more trains in the future. That work is expected to be complete next year, according to the CTA.

On top of increasing capacity, the city is also working to implement upgrades to increase the speed of Blue Line service. Known as the FastTracks program, the initiative is funded through a city surcharge on trips with ride-hailing companies like Uber and Lyft.