From the Metra station at Halsted Street (MP 1.8), the Four Main Track line continues due west, with two extra tracks on the south side of the line, with a UP (ex-C&NW) connection west from the St. Charles Air Line running parallel just to the north. There are signal bridges surrounding crossovers just west of the station. The line is on viaduct, with South Halsted Street, South Peoria Street and South Morgan Street passing below. A branch from Canalport on the Chicago River trails in from the south, at a signal bridge, and the UP (ex C&NW) Global I East intermodal yard (on the site of the former B&OCT Robey Street Yard) lies alongside to the north and there are extra tracks on the south side. South Racine Avenue passes below, and then South Blue Island Avenue does so at an angle, followed by South Loomis Street, South Latlin Street, South Ashland Avenue, and South Pauline Street.
Both BNSF and UP lines pass beneath the CTA ("Elevated") steel trestle viaduct near the CTA 18th Street station, followed by South Wood Street passing below, west of which lies the UP (ex-C&NW) Global I West intermodal yard (once known as Wood Street Yard), as the ex-CB&Q main line turns west-southwest, with the recently closed (in early 2006) BNSF Western Avenue Yard on its north side, ending adjacent to the Metra Western Avenue station (MP 3.7), with umbrella sheds on its platforms, west of which the eponymous avenue passes below, from which a leg of a wye departs to the southwest to connect to a line on the east side of the ex-Chicago Junction, ex-B&OCT, and ex-PRR tracks heading north-south in this area, down to the Canalport line at 25th Street crossing, with a west leg of that wye trailing in just before the main line bridges over the ex-Chicago Junction, ex-B&OCT, and ex-PRR tracks below.
The speed limit is 45 mph for passenger trains and 15 mph for freights from MP 1.7 to MP 2.1, 60-25 west of MP 2.1, and 70-30 west of MP 4.0.