From the junction at Gratiot (MP 0.0), where there is a tower on the south side of the line, the TRRA MacArthur Bridge District heads east-southeast towards the eponymous bridge, with a flat crossing over the ex-MP tracks at the east end of its 23rd Street Yard, while the Merchants District turns away to the east on the north side of the ex-MP tracks. The MacArthur Bridge District is entirely built on the steel trestlework of the MacArthur Bridge approaches, except where it crosses the bridge itself.
The Two Main Tracks (2MT), Traffic Control System (TCS) line, speed limit 25 mph, bridges over Cerre Street, 7th Street, Gratiot Street, 6th Street, a stub of track owned by Manufacturers Railway, Broadway, 4th Street, I-55, 3rd Street, 2nd Street, 1st Street and the UP (former MP) line along the west bank of the river, to South Approach (MP 0.5), where the line coming north from UP Connection trails in on the south side.
A single track, TCS, line, with speed limit 10 mph, climbs northward from the UP (former MP) and Manufacturers Railway lines along the west bank of the river, at UP Connection (MP 0.0), bridging above 1st Street twice and then over the UP (former MP) line along the west bank of the river, to South Approach (MP 0.8).
This segment of track comprises the MacArthur Bridge itself, a compound through truss bridge with two decks, one built to carry a street (closed some years ago), and one carrying a double track railway line from South Approach (MP 0.5) across the Mississippi River to North Approach (MP 1.0), 2MT, TCS, speed limit 25 mph.
At North Approach (MP 1.0), there is a double track junction, with 2MT, TCS, continuing east towards East Approach, and 2MT, TCS, turning northeast, with speed limit 10 mph, bridging over two separate lines heading south and southeast from the TRRA Wiggins #5 Yard, then over the curving lanes of Illinois Route 3 heading south from its junction with I-55/70, over I-55/70 itself (five total roadways), and then over TRRA and Gateway Western lines at their M&O Junction (below), two different Gateway Western lines coming north-northwest to their Hole-in-the-Wall (below), a street passing below, Intermediate Signals on a signal bridge, bridging over the St. Louis Metrolink/BiState Light Rail Line heading southeast at this point (on the former right-of-way of the Pennsylvania Railroad), and an east-west street, passing the former location of East St. Louis Union Station, three road bridges overhead, and a junction with the TRRA line coming northeast from M&O Junction at Q Tower (MP 2.2), where a number of lines coming east from the river bank used to cross at grade, and today's line splits into a TRRA line heading north-northwest to Bridge Junction, a TRRA line heading north-northeast (the Eads Conologue Distirct), a Gateway Western (formerly PRR) line heading northeast and a CSX (formerly B&O) line heading northeast, all past the former location of Relay station just north of Q Tower.
At North Approach (MP 1.0), there is a double track junction, with 2MT, TCS, turning northeast, and 2MT, TCS, continuing east, with speed limit 25 mph bridging over a lines heading south from the TRRA Wiggins #5 Yard to the erstwhile route of the former Southern line in this area, a TRRA and Gateway Western line heading south through their Southern crossing, below, and two separate Gateway Western lines heading south-southeast, and turns southeast, passing over the former right-of-way of the East St. Louis, Columbia & Western electric railway to East Approach (MP 2.6), where there is a double double track junction, with one set of tracks continuing southeast towards ALS Connection, and the other curving south-southwest to Valley Junction.
At East Approach (MP 2.6), there is a double double track junction, with one set of tracks curving south-southwest to Valley Junction and the other continuing southeast, bridging over the TRRA Illinois Transfer District tracks heading south-southwest, to ALS Connection (MP 3.4), where an Alton & Southern line from Valley Junction trails in from the west-southwest, and the Alton & Southern continues southeast at its Gateway Yard.
At East Approach (MP 2.6), there is a double double track junction, with one set of tracks continuing southeast towards ALS Connection, and the other curving south-southwest to Valley Junction (MP 3.4), where the tracks trail into the TRRA Illinois Transfer District already heading south-southwest.