UP Skokie River Bridge

In the late 19th Century, Chicago grew to the prominent railroad hub in the central United States. Chicago also served as the dividing point between the railroads operating in the east and railroads operating in the Midwest.  The Chicago & North Western Railway (C&NW) had constructed a network of railroad lines, radiating north and west from Chicago.  Until a freight bypass was constructed in 1889, all freight traffic from Wisconsin was required to enter downtown Chicago.  In the early 20th Century, the C&NW invested heavily in rebuilding existing lines, opening new lines and improving operations.  In 1903, subsidiary Chicago Northern Railway Company (CNR) constructed 22 miles of double track railroad between the Mayfair-Evanston freight bypass at River Junction (present day Bryn Mawr Avenue), northwards into Lake County, before turning east to reach the existing C&NW mainline at Lake Bluff, Illinois.  Further double track extensions came in 1905-1906, when the Chicago & State Line Railway constructed 16 miles between Tower KO (Lake Forest) and the Wisconsin state line; and the Milwaukee & State Line Railway constructed 34 miles between the state line and St. Francis, Wisconsin; where it joined the existing C&NW mainline between Chicago and Milwaukee.  Also in 1908, the C&NW constructed a short 2.3 mile double track line between St. Francis, Wisconsin and the existing C&NW mainline between Milwaukee and Madison at Chase (South Milwaukee).  The two railroads were formally consolidated into the C&NW in 1909.

Another double track line was constructed beginning in 1911. Subsidiary Des Plaines Valley Railway (DPV), constructed 11 miles of railroad connecting the Proviso Yard, located east of Elmhurst, to the Wisconsin Division mainline near Des Plaines.  The following year, an additional 10 miles were completed to Valley, located in present-day Northbrook.  In addition, the Milwaukee, Sparta & North Western Railway (MS&NW) constructed a short 8-mile double track line between the existing C&NW mainlines at Butler, Wisconsin and West Allis, Wisconsin in 1911.  It is believed that the C&NW double tracked the existing line between West Allis and Chase at this time.  The MS&NW was formally merged into the  merged into the C&NW in 1912, followed by the DPV in 1913.  The route from St. Francis to Proviso formed a second freight bypass of Chicago, allowing freight from Wisconsin to reach the hump yard at Proviso.  This cutoff became a critical portion of the C&NW network, providing a bypass of Chicago and a main way to reach the Proviso Yard from all three principal mainlines of the railroad.  The line between Butler and West Allis provided a bypass of Milwaukee, improving operations in the area.

The C&NW would become a prominent railroad in the Midwest, eventually building a system over 11,000 miles long.  Portions of this route were relocated in 1954 to accommodate an expansion of O'Hare International Airport.  Much of the second track between Gurnee and St. Francis would be removed in 1960.  By 1968, deteriorated track conditions between Dempster Street and Valley resulted in the C&NW acquiring and operating the parallel Chicago, North Shore & Milwaukee Railway trackage.  In 1988, the C&NW abandoned the tracks between Oakton Street in Skokie and River Junction. In 1995, the C&NW would be purchased by the Union Pacific Railroad.  UP abandoned the Skokie to Valley segment in 2004.  Today, UP continues to operate the Milwaukee Subdivision between Proviso and Butler, and it continues to provide a critical freight route around Chicago.