The only support for this oft-told tale is an unsourced statement in Mike Royko's book
Boss.
All of Chicago's radial expressways were planned in the 1930s to run alongside existing railroad lines where they would not require large-scale demolition and divide neighborhoods. (This wasn't possible for the east end of the Congress Superhighway, but Edward Bennett and others strongly argued for the Congress Parkway location anticipated in the
Plan of Chicago.) There were three possibilities for an expressway entry into Chicago from the east or south. A lakefront alignment next to the Illinois Central became problematic with the growth of truck traffic in the 1930s, leaving the NYC/RI alignment at State Street or the C&WI alignment at 400W.
The north end was originally planned next to the C&WI, requiring a bizarre jog along 36th Street. In 1956 it was shifted to run next to the Rock Island Line at State Street, the official reason being “better alignment and traffic distribution.”
Looking at this map, I'm hard pressed to see how the final alignment is any better than the original at "walling off" the Black Belt from Daley's Bridgeport. I think the logic of the more direct route is certainly the primary reason, but the 1956 alignment also took advantage of empty urban renewal land and required condemnation of industrial property rather than thousands of homes.
http://i44.tinypic.com/1fg0eu.png
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