Illinois Route 394
Length: 4.8 miles
Termini: Expressway ends at US 30 near Ford Heights and starts at the I-294/80/94/US 6 junction in South Holland.
Reason for being a state route: Although the number does warrant being an Interstate, and probably does not violate AASHTO standards, Illinois was reluctant to give the route I-394 because the southern section from US 30 to IL 1 was not upgraded. So no funds. (Like the horrible Embarcadero Crappaway in SF not being I-480 because it wasn't completed to US 101...)
History: The southern extension of the Calumet Expressway was built in 1962, with freeway status to US 30 near Ford Heights. This gave access between the southern suburbs like Chicago Heights and Park Forest and downtown Chicago.
From Rich Carlson's site:
If the Peotone Airport is ever built this could become I-394, but this is unlikely for at least several years. Maps show the location of the proposed airport at the SW quadrant of the IL-394/IL-1 intersection.
So I-394 the designation is not dead...but I assume that an upgrading from IL 1 to US 30 is necessary in order for the entire route to be I-394. But, like CA 905 and former IN 469, this route can (and maybe will) become an interstate.