The Chicago Subdivision or Chicago Sub is a railroad line in Illinois that runs about 38 miles (61 km) from Chicago to Aurora and hosts Metra's BNSF Railway Line commuter service. It is operated by BNSF Railway as the easternmost part of the railroad's Northern Transcon to Seattle, Washington. This line is known as the Racetrack because it is mostly triple-tracked and supports fairly fast trains. It had been operated by a BNSF ancestor, the Chicago, Burlington and Quincy Railroad, which introduced high-speed Zephyr passenger trains in 1934 and ran many of them along this subdivision from Chicago to points west.
Amtrak's Carl Sandburg on the Chicago Subdivision in Berwyn, Illinois. The bridge above the train belongs to the Canadian National Railway (previously Illinois Central).
The Northern Transcon, a route operated by the BNSF Railway, traverses the most northerly route of any railroad in the western United States. This route was originally part of the Chicago, Burlington and Quincy Railroad, Northern Pacific Railway, Great Northern Railway and Spokane, Portland and Seattle Railway systems, merged into the Burlington Northern Railroad system in 1970.
The Empire Builder crosses the Two Medicine Trestle at East Glacier Park, Montana on the Hi Line Subdivision in 2011.