In 1968, a southward-facing connection was built, generally known as the South Leg because together with the original lines a wye was formed which was occasionally used to turn passenger trains around.

This coincided with the gradual elimination of yards to the north (this area is the Illinois Center office, hotel, and retail complex today).

[1] Chicago has since reversed its position, adopting plans to run more transit and intercity passenger trains on the St. Charles Air Line.

[3] Amtrak's City of New Orleans, Illini, and Saluki utilize this line with a time-consuming switchback into Union Station from its west end.

The Chicago Region Environmental and Transportation Efficiency Program (CREATE) is in the preliminary design phase for the Grand Crossing Project.

As of October 2021, a large project was nearing completion to replace a bridge passing over the future Wells Street Extension, and rebuild retaining walls on both lines between the 16th St. interlocking and the Chicago River.

The realignment changed a double-track section to single track in an east-west corridor running north of 16th St., which originally consisted of four elevated lines laid over two parallel series of viaducts that cross five streets and two alleys.

[6] In 2022, Amtrak began seeking grants to build a direct connection between the St. Charles Air Line and Union Station to avoid the switchback maneuver.

[7] As part of the congestion relief effort, Amtrak wanted to reroute its Michigan and East Coast trains onto the St. Charles Air Line after the Union Station direct link was made,[8] and it applied for funding to restore the roughly 1 mile (1.6 km) double-track alignment that CN just removed.