The Union Pacific Northwest Line (UP-NW) is a commuter rail line provided by Metra and operated by the Union Pacific Railroad in Chicago, Illinois and its surrounding suburbs. While Metra does not refer to any of its lines by colors, the timetable accents for the Union Pacific Northwest Line are bright "Viking Yellow," honoring the Chicago & North Western Railway's Viking passenger train.

Metra is the primary commuter rail system in the Chicago metropolitan area serving the city of Chicago and its surrounding suburbs via the Union Pacific Railroad, BNSF Railway, and other railroads. The system operates 242 stations on 11 rail lines. It is the fourth busiest commuter rail system in the United States by ridership and the largest and busiest commuter rail system outside the New York City metropolitan area. In 2023, the system had a ridership of 31,894,900, or about 152,400 per weekday as of the fourth quarter of 2023. The estimated busiest day for Metra ridership occurred on November 4, 2016—the day of the Chicago Cubs 2016 World Series victory rally.