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I-870 (numbered as another interstate) Illinois
The 870 numbering follows from the late 1970s plan to apply I-270 to the entire circumference of the St. Louis beltway, instead of the shared 270/255 numbering in place today.  This would have left an extra "tail" of today's I-270 not part of the circle to be named I-870.
I need a new status code for "shoved up ass"
Kim Harvey writes: "The rumors behind this is that locals allegedy approved the route, but told Idot to take that 870 and shove it up their ass. The draft eis has all those comments from local leaders and all of them from Madison County had one view in common: leave 270 as is." 
See also: Map of I-870 (Stephen Summers; from Draft EIS, I-270 between Collinsville and I-70, c. 1980)