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CHICAGO — Mayor Lori Lightfoot and the president of the Chicago Transit Authority will break ground on the Red and Purple modernization project Wednesday.

This is a big project to help relieve congestion on those lines. In phase one of the work, the CTA will start to build a new bypass north of Belmont so northbound brown line trains can go up and over the Red and Purple tracks, meaning trains won’t have to stop and wait for others to pass.

The CTA will also rebuild century-old track structure and redo the Lawrence, Argyle, Berwyn and Bryn Mawr stations.

The project is expected to be completed in 2025.