We have our little branch of it here. We have four interstates that merge at that bridge (I-70, I-40, I-44, and I-55)I think 40 disappears in Illinois and becomes I-64 heading to Kentucky or Tennesee. Out here in St. Louis county though the road is highway 40 or I-40.
Not to nitpick, but I-40 is a couple-hundred miles south of St. Louis, and runs through Arkansas and Tennessee; it does not enter Illinois or Missouri. US 40 parallels I-70 in the St. Louis area, as it does for much of it's run all the way out to the east coast.
The four interstates in downtown STL are I-44 (goes southwestward toward Tulsa & Oklahoma City - where it intersects I-40), I-70 (eastward with US 40 to Indianapolis and points east; Kansas City & points west), I-55 (north to Chicago; south to New Orleans), and I-64 (it ends west of St. Louis along US 40 prior to an intersection with I-70; it runs eastward to Louisville and eventually Norfolk).
Missouri Interstate highway list