Chicago Subdivision

{{Short description|Railroad line in Illinois, United States}}

{{Use American English|date=February 2025}}

{{About|the Chicago–Aurora railway line|the Chicago–Sabula railway line|Iowa, Chicago and Eastern Railroad}}

{{Infobox rail line

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| name = Chicago Subdivision

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| image = Carl Sandburg train.jpg

| image_width = 300px

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| caption = 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).

| type = Freight rail
Commuter rail
Inter-city rail

| system = Northern Transcon

| status =

| locale = Chicago metropolitan area

| start = Chicago

| end = Aurora, Illinois

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| owner = BNSF Railway

| operator = BNSF Railway
Metra
Amtrak

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| linelength_km =

| linelength_mi = 38

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| tracks = 3-4

| gauge = {{RailGauge|sg|al=on}}

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| speed_mph = 70

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| website =

| map = {{Chicago Subdivision}}

| map_state = collapsed

}}

The Chicago Subdivision or Chicago Sub is a railroad line in Illinois that runs about {{convert|38|mi}} from Chicago to Aurora and hosts Metra's BNSF Line commuter service. It is operated by BNSF Railway as the easternmost part of the railroad's Northern Transcon to Seattle, Washington.{{cite web|url=http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Eola%20to%20Aurora.htm|archive-url=https://web.archive.org/web/20110710144538/http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Eola%20to%20Aurora.htm|url-status=usurped|archive-date=July 10, 2011|title=Eola to Aurora|author=Don Winter|accessdate=June 4, 2010}}{{cite web|url=http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/La%20Grange%20to%20Eola%20%28CB&Q%29.htm|archive-url=https://web.archive.org/web/20110710144543/http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/La%20Grange%20to%20Eola%20(CB&Q).htm|url-status=usurped|archive-date=July 10, 2011|title=La Grange to Eola (ex-CB&Q)|author=Don Winter|accessdate=June 5, 2010}}{{cite web|url=http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Cicero%20to%20La%20Grange%20%28CB&Q%29.htm|archive-url=https://web.archive.org/web/20110710144547/http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Cicero%20to%20La%20Grange%20(CB&Q).htm|url-status=usurped|archive-date=July 10, 2011|title=Cicero to La Grange (ex-CB&Q)|author=Don Winter|accessdate=June 5, 2010}}{{cite web|url=http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Western%20Avenue%20to%20Cicero%20%28CB&Q%29.htm|archive-url=https://web.archive.org/web/20110710144551/http://donwinter.com/Railroad%20Infrastructure%20and%20Traffic%20Data/Regions/Chicago/Route%20Descriptions/Western%20Avenue%20to%20Cicero%20(CB&Q).htm|url-status=usurped|archive-date=July 10, 2011|title=Western Avenue to Cicero (ex-CB&Q)|author=Don Winter|accessdate=June 5, 2010}} This line is colloquially 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.

The Chicago Subdivision meets the Aurora Subdivision and Mendota Subdivision in Aurora. Commuter service ends at the Aurora Transportation Center, though Amtrak trains continue southwest on the Mendota Subdivision. Triple-tracking runs from where track leading to the Aurora station and Metra Yard joins the subdivision eastward to Cicero, where multiple tracks from a yard join. It is then quadruple-tracked for the rest of the way until the turn to Union Station.{{cite web|url=http://web.me.com/willvdv/chirailfan/mmbnsf.html|title=Railfan tips/operating detail|author=Bill Vandervoort|work=Chicago Transit & Railfan|accessdate=June 4, 2010}} {{As of|2015}} weekday traffic on the subdivision was 94 Metra commuter trains, eight Amtrak intercity trains, and 60 BNSF freight trains.{{cite journal | title=Metra mojo | author=Blaszak, Michael W. | journal=Trains |date=March 2015 | volume=75 | issue=3 | pages=53}}

After the introduction of the CB&Q Zephyrs, train speeds increased significantly around the country for the next decade or so, but the Naperville train disaster along these tracks in 1946 was one event that contributed to the federal government restricting speeds in later years. Trains that had once traveled at or above {{convert|100|mph}} were soon restricted to a maximum of {{convert|79|mph}}.{{cite web|url=https://groups.yahoo.com/group/steam_tech/message/54227|archive-url=https://archive.today/20120709213710/http://groups.yahoo.com/group/steam_tech/message/54227|url-status=dead|archive-date=July 9, 2012|title=Hiawatha dieselization|author=William Wendt|publisher=Yahoo Groups|date=July 30, 2007|accessdate=June 5, 2010}}{{cite book|author=John Gruber and Brian Solomon|title=The Milwaukee Road's Hiawathas|publisher=Voyageur Press|date=2006|isbn=978-0-7603-2395-3}}{{cite web |url=http://www.trains.com/trn/default.aspx?c=a&id=4424 |archive-url=https://web.archive.org/web/20100624120252/http://www.trains.com/trn/default.aspx?c=a&id=4424 |url-status=dead |archive-date=June 24, 2010 |title=Ask Trains from November 2008 |date=December 23, 2008 |publisher=Trains Magazine |accessdate=June 5, 2010 }} Much of this line has a speed limit of {{convert|70|mph}} for passenger trains, while freight trains run slower.