The CTA’s upcoming $2.1 billion Red and Purple Line Modernization (RPM) Program has one less hurdle to clear as crews complete nearly $4 million in track reconstruction near Addison.

The improvements eliminate a “slow zone” and provide customers a smoother ride and more reliable service. More importantly, it clears a path for major construction on the first phase of the RPM project to begin in earnest later this year.

As the most expensive capital improvement project in the history of the Chicago Transit Authority, the RPM program will rebuild four of the Red Line’s oldest stations—at Lawrence, Argyle, Berwyn, and Bryn Mawr—into larger, fully accessible structures.

It includes additional track and signal improvements as well as the $570 million “Belmont Flyover,” which replaces a congested junction where the Purple, Brown, and Red line intersect. While the rail bypass won’t break ground until next year, the CTA has already started demolishing a handful of Lakeview buildings and relocating utilities in anticipation of the project.

“These improvements will have benefits for the entire CTA system,” said Chicago Transit Authority president Dorval R. Carter, Jr. at a press conference on Friday. “By improving the flow of trains, we are able to add additional reliability across the rest of the network.”

“This system was built when Roosevelt was president—Teddy Roosevelt,” said Mayor Rahm Emanuel. “It’s done a good job but has outlived its design. After 100 years of taking a band aid approach, today marks the beginning of an unprecedented, comprehensive investment to modernize the system to handle more trains with greater speed and reliability.”

The Red and Purple Line Modernization Program is expected to be complete in 2025. It is funded through $1.1 billion in federal money and a special, transit-specific tax increment financing (TIF) district. The CTA awarded a $1.2 billion contract to a joint venture of Chicago-based Walsh Construction and Texas-based engineering firm Fluor Corporation to design and build the stations.