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I-494 (cancelled) Illinois
This number was applied to several proposed routes:
This was killed around 1980. It would have been 8 lanes and cost nearly $2 billion. The federal funds were reportedly traded in for projects like the O'Hare rapid rail extension, the Midway rapid rail extension, and I-39. 
2) Lakeshore Drive (now US 41.) Some accounts had this going from the IL/IN state line at I-94 to near Waukegan built largely on fill along the shore of Lake Michigan, but this was quickly squashed by North Shore residents not wanting the beaches replaced by an expressway. 
A 1962 map (courtesy Stephen Summers) shows I-494 starting at today's I-90 tollway near Chatham, intercepting US 41 near 57th Street, and following Lake Shore Drive to just north of the Chicago River. Then it veered west, using the Ohio Street ramps to reconnect with I-90/94 northwest of the Loop.