[kasey_junk]

Chicago put the major north/south and east/west highways where they are to make areas more clearly delineated between residential and commercial.

They did this for a variety of reasons some noble (grand visions of urban renewal based on cars instead of public transit) and some odious (breaking up non-machine voting wards, enforcing de facto redlining post the Supreme Court decisions, etc). They were able to make sections of the city, specifically the near south and south west places you commuted through instead of to. Similar things were done with tearing out el tracks, trolleys and the removal of commuter rail from further south neighborhoods that had been alternate business districts to the loop. These were conscious urban planning decisions to reinforce the pattern of outward/in commutes.

American Pharoah is a not particularly good biography of Richard Daley that happens to include a good book on Chicago urban planning in the late 40s to late 60s era.