Dusting off this thread rather than creating a new one . . .
Found this 1960 planning document for East St. Louis:
https://openscholarship.wustl.edu/cgi/viewcontent.cgi?article=1018&context=books.
The map on Page 28 of 149 has an alternate design for the PSB Complex with a loop ramp for the Pigott to PSB movement, a farther south location of the unbuilt corridor to Belleville (called the "Belleville Radial"), and a proposed but never built "12th Street Radial Connector Link" freeway that would have linked the Belleville Radial to I-64 around 21st Street.
Also very interesting is the map on Page 13 of 149:
* It shows an outer belt route from Columbia to Troy similar to the dead Gateway Connector, but farther west (would have crossed I-64 a little east of IL 159).
* It shows the originally planned alignment for I-70 that split from I-55 near the US 40 interchange.
* It shows the earlier alignment for I-55 in St. Louis where I-55 and the unbuilt North-South Distributor would split south of Gravois.
* It shows a corridor stretching north from the I-55/I-64/I-70 interchange along IL 3. The corridor is shown with a line similar to other freeways and has a shield similar to that used for interstates but is missing the "I" from "FAI". The number appears to be 155. While it does appear that there was a "Federal Aid 155" (from snippets through Google Books for the highway to Alton), I really have to wonder if that number was coincidence or some unrealized plan.