From the 1952 annual report of the Missouri Highway Commission, contributed by David Backlin, this picture shows US 40 and 61, probably where what was then Bypass US 40 branched off at Wentzville. I-70 follows the old Bypass 40 route. By this point, the highway may already have been a four-lane divided highway. It was four lanes by 1957, according to the official Missouri highway map for that year.
Image courtesy of David Backlin