A few major construction projects were carried out in Chicago, impacting certain railroads including grade separations.

March 2, 1914
Ordinance for construction of new Belt Railway of Chicago Clearing Yard, and construction of 59th Street Line providing access to west end of Clearing Yard. Ordinance also provided for Cicero Ave. and Crawford Ave. (now Pulaski Rd.) viaducts over railroad east of Clearing Yard. The 59th Street Line, after diverging from the main line, originally followed 59th St. west of Cicero Ave. This line actually bisected the square mile of land which later became Chicago Municipal Airport, now Midway Airport. The airport originally was confined to the land south of 59th St. But with the growth of air travel and the development of larger aircraft requiring longer runways, the Chicago City Council recognized the need to expand the airport north of 59th St. An ordinance was passed January 25, 1937, requiring the Belt Railway of Chicago to shift its line north, paralleling the Indiana Harbor Belt Stock Yards Line which was north of 55th St.

July 21, 1919
Ordinance for development of Lakefront land south of downtown Chicago, between Roosevelt Rd. and 47th St. In that area, the Illinois Central line had been immediately next to Lake Michigan. The plan called for construction for new park land east of the railroad. The park land would be accessed via several new viaducts over the railroad, and a subway under the railroad at 47th St. The most significant requirement of this ordinance, was the electrification of all Illinois Central operations, initially with the commuter service. This would eliminate the smoke pollution from the steam locomotives. The commuter service was electrified in 1926. But with the later development of diesel locomotives, the electrification was not carried out for the through passenger and freight trains.

July 8, 1926
Ordinance for straightening of the Chicago River south of downtown Chicago. The Baltimore & Ohio line south of Grand Central Station would be most significantly impacted, as it originally crossed at a bend in the river north of Roosevelt Rd. A new bridge would need to be constructed at 16th St., parallel to a relocated bridge of the St. Charles Air Line. West of the river, both railroads would be elevated crossing Canal St.

May 26, 1944
Ordinance for grade separations of Baltimore & Ohio Altenheim Line and paralleling rapid transit line, where they would be paralleled by planned West Route of the Comprehensive Superhighway System. An October 31, 1940 ordinance had approved this West Route of the Comprehensive Superhighway System, which later became known as the Eisenhower Expressway. These grade separations would include a subway for Central Ave., and a depressed railroad right of way under Austin Blvd.