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.[5] As of 2015[update] weekday traffic on the subdivision was 94 Metra commuter trains, eight Amtrak intercity trains, and 60 BNSF freight trains.[6]
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 100 miles per hour (160 km/h) were soon restricted to a maximum of 79 miles per hour (127 km/h).[7][8][9] Much of this line has a speed limit of 70 miles per hour (110 km/h) for passenger trains, while freight trains run slower.[1][2][3][4]