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This configuration was due to geography and traffic patterns in the Loop. Unlike most parts of the rest of the city near the river, most downtown streets crossed the river. All of these crossings are done by bascule bridges and each bridge required height clearances at the approaches to and over the river. Further necessitating clearances were many existing railroad tracks that were along the river (as in the west bank of the south branch) or tracks that ended at the river (for example the tracks ending at Randolph Street). Thus along the river at points of many closely spaced crossings, a clearance zone was created. Many double-decked or triple-decked streets came into being as a result of falling within this clearance zone.
|Upper & Lower Wacker Drive on the Chicago River.|
The first raising occurred from 1855 to 1858, when streets and buildings were raised between four and seven feet above their former elevation, just a few feet above lake level, where they were constantly muddy. The higher elevation allowed for sewers and proper drainage. However, this did not produce any two-level streets; the first of those was Michigan Avenue in the late 1910s. When the Illinois Center development was built on the east side of downtown, a new upper level was built, making most streets in that area three levels.
After about 1890, special interest groups, including recreational bicyclists, farmers delivering harvested crops to market, and motorists, began to mount support for concrete paving to replace the previously common dirt roads. Public road planning in Chicago began in 1910 when the Chicago Plan Commission was created to implement Daniel Burnham and Edward Bennett's plan.
The double-decked portion of Wabash Avenue north of the Chicago River was built in 1930, in conjunction with the single-level Wabash Avenue Bridge. On January 3, 2005, the upper and lower levels were closed at Kinzie Street for reconstruction (in conjunction with the Trump Tower Chicago development) but have since been reopened.