CHICAGO (CBS) — The CTA officially broke ground Wednesday on a huge new project to make the commute easier for riders who take the Red, Purple, and Brown lines on the North Side.

Mayor Lori Lightfoot and U.S. Sen. Dick Durbin were on hand for what they called a “historic day” for the CTA, as crews gathered for the launch of the first phase of the $2 billion Red & Purple Modernization project.

The first phase of the massive project will completely rebuild the Lawrence, Argyle, Berwyn and Bryn Mawr ‘L’ stations, as well as more than a mile of tracks and support structures.

Crews also will build the Red-Purple Bypass north of the Belmont station, a project to build a new “flyover” for northbound Brown Line trains north of Belmont.

The new flyover would eliminate a bottleneck at a 100-year-old junction for Brown, Red, and Purple line trains by allowing northbound Brown Line trains to travel above southbound Red and Purple line tracks, rather than crossing through them. The flyover would allow the CTA to run up to 15 extra trains an hour on the Red, Brown, and Purple line tracks.

Current layout of CTA tracks at a junction of the Brown, Red and Purple Lines in Lakeview, requiring other trains to wait for northbound Brown Line trains that have to cross three sets of tracks at the intersection. (Credit: CTA)

Current layout of CTA tracks at a junction of the Brown, Red and Purple Lines in Lakeview, requiring other trains to wait for northbound Brown Line trains that have to cross three sets of tracks at the intersection. (Credit: CTA)

Future layout of CTA tracks at a junction of the Brown, Red and Purple Lines in Lakeview, eliminating a bottleneck by creating a dedicated elevated track for northbound Brown Line trains, rather than having them intersect three other sets of track. (Credit: CTA)

Future layout of CTA tracks at a junction of the Brown, Red and Purple Lines in Lakeview, eliminating a bottleneck by creating a dedicated elevated track for northbound Brown Line trains, rather than having them intersect three other sets of track. (Credit: CTA)

Officials expect the bypass to be complete by 2021. The station construction is expected to be complete by 2025.