Metra's LaSalle Street Station (MP 0.0) is located a block further south than the old Rock Island station of the same name, with its station facilities inside an office building at that location, but using (a shortened version of) the same platforms and tracks once used by the old station. There are five platforms, with umbrella sheds, serving eight tracks, passing over a street below at the end of the platforms. The throat of the station, with three tracks passing beneath two signal bridges, is controlled by Polk Street Tower (MP 0.3), with a road bridge overhead and another signal bridge, after which the line edges to the east, with derelict land where the former Rock Island TOFC Yard, later used by Chicago Rail Link, was once on the west side of the line.
Heading due south again, the line passes a street alongside to the east, and a signal bridge, crosses the St. Charles Air Line and the former IC connection to the west side at grade at 16th Street Tower (MP 1.1), crossing each line at a separate flat crossing (four total on each north-south line). The line then passes crossovers and signals, passes beneath the elevated CTA concrete viaduct carrying the CTA Orange Line, turns east-southeast and passes beneath the elevated CTA steel viaduct carrying the CTA Red Line, and then turns due south again, with the Dan Ryan Expressway (I-94) alongside to the west, past two bridges over east-west streets, a signal bridge, a bridge over an east-west street., a bridge over a limited access divided highway, five bridges over east-west streets, and crossovers just north of MP 3.73.
At Root Street Tower (MP 3.9), on the east side of the line there is a large wye on the west side connecting with the former Chicago Junction tracks west to the yard at Ashland Avenue, and the former location of a flat crossing (in the center of the wye) with an erstwhile Rock Island track to the east (which once connected with the Illinois Central main near 39th Street), while the main line continues south.