Milwaukee District West Line

The Milwaukee District West Line (MD-W) is a Metra commuter rail line in Chicago, Illinois, and its western suburbs. Metra does not refer to any of its lines by a particular color, but the timetable accents for the Milwaukee District West line are dark "Arrow Yellow," honoring the Milwaukee Road's Arrow passenger train. Trains are dispatched from the Canadian Pacific Kansas City Railway's American headquarters in Minneapolis.

The line runs from Chicago Union Station through the western suburbs to Elgin, Illinois. As of February 15, 2024, the public timetable shows 52 trains (26 in each direction) operating on weekdays. Of these, 19 inbound trains originate from Big Timber Road, three from Elgin, one from National Street, and three from Franklin Park. Three outbound trains terminate at Franklin Park, one at National Street, and the remainder terminate at Big Timber Road.

On weekends, Metra operates 12 roundtrips on Saturdays and nine on Sundays and holidays, all running from Union Station to Elgin. There is no weekend or holiday service to Big Timber Road.

The line runs on the CPKC Railway's Elgin Subdivision (ex-Milwaukee Road line to Omaha). In 1982, the Milwaukee Road Elgin Line was sold to the newly created Northeast Illinois Regional Commuter Rail Corporation which ran commuter trains for the Milwaukee Road while the latter underwent reorganization. The Milwaukee Road retained ownership of the line until 1986. Metra formally purchased the Milwaukee District (the only other being Milwaukee District North) from the Soo Line Railroad (which took the bankrupt Milwaukee Road under its wing in 1985) in 1987. The Soo Line then ran freight trains on the line via trackage rights until it was absorbed into the Canadian Pacific Railway in 1990. CP Railway merged with the Kansas City Southern Railway in April 2023 into the Canadian Pacific Kansas City, or CPKC.

Metra has included the possibility of extending the Milwaukee District West Line along one of two routes in their Cost Benefit Analysis report. If this were to happen, the line could continue west via CPKC trackage to Hampshire, with an additional stop in Pingree Grove. Alternatively, the line could switch to the Union Pacific Railroad's Belvidere line (ex-Chicago & North Western line to Freeport) and travel northwest from Big Timber Road to Marengo, with additional stops in Gilberts, Huntley, and Union. In 2023, Governor J. B. Pritzker selected Metra to operate new intercity passenger rail beyond Big Timber Road to Rockford using the Milwaukee District West Line, with intermediate stops in Belvidere, Huntley, and at one of the three existing Metra stations in Elgin. The service would provide additional capacity to the existing line; introducing express reverse commute and expanded weekend options between Elgin and Union Station. The extension is scheduled to open in 2027, making it the first passenger rail service to connect Chicago and Rockford after the discontinuation of Amtrak's Black Hawk service in 1981.