East of Halsted Street and west of the Union Avenue connection, on the former CB&Q, Amtrak trains stop and reverse, over the junction at Union Avenue, past the signal bridges for the junction, and two bridges over streets, onto the double track St. Charles Air Line viaduct, past a wide road bridge overhead (I-90/94), and a bridge over a street, passing over the top of the lines coming south out of Chicago Union Station, with the former routing of the B&OCT line into Grand Central Terminal just to the north (with its bridge severed at the western end, before crossing the CUT lines), crossing over the Chicago River on a through truss bascule lifting bridge (with the permanently open B&OCT bridge of similar type just to its north, with its viaduct ending at the east bank of the river), bridging over a dirt track (formerly a rail line) on a through girder bridge, and descending to ground level, with a connector south to the Metra Rock Island District line, and a flat crossing (16th Street Crossing) over the Metra Rock Island District tracks coming south out of La Salle Street Station, with the 16th Street Tower in the southwest quadrant of the flat crossing, to the junction at Clark Street, on a through girder bridge over the eponymous street..
From 21st Street (MP 2.6), the Illinois Central tracks that run along the northwest side of the route of the former C&WI tracks into Dearborn Station head northeast, past the former location of Santa Fe's 18th Street Passenger yard on the east side, with the CTA Orange Line's elevated tracks occupying part of that site, and climb gently towards a connection with the St. Charles Air Line, making a flat crossing with the southwest quadrant connector from the Union Avenue line and a flat crossing (also 16th Street Crossing) over the Metra Rock Island District tracks coming south out of La Salle Street Station, to the junction at Clark Street (MP 2.0), on a through girder bridge over the eponymous street, where the Union Avenue and 21st Street lines come together and continue east, past the location where they bridged over the C&WI tracks into Dearborn Station, a through girder bridge over Dearborn Street and a through girder bridge over State Street, under the CTA elevated coming south from The Loop, a through girder bridge over Wabash Avenue, as the line passes between the buildings to the north and south, a through girder bridge over an alley, a through girder bridge over Michigan Avenue, a through girder bridge over an alley, and a through girder bridge over Indiana Avenue, to the signals at South Wye Junction (MP 1.2), where there was once a wye with the line coming south from (Illinois) Central Station and today's line turns south-southeast.
The speed limit is 10 mph across this entire single track line.