Business Loop I-70 - St. Charles

Old Bypass U.S. 40, Business Loop I-70 follows First Capitol Drive and Fifth Street between Exits 228 and 229. U.S. 40 follows a freeway along side both Interstate 64 and U.S. 61 from Wentzville southeast through St. Charles County. U.S. 40 Bypass was replaced by I-70 (Mark Twain Expressway) east from Wentzville to Bridgeton, and Interstate 270 east from I-70 to Illinois.

According to a Rand McNally map of St. Louis from 1964, Business Loop I-70 in St. Charles once followed West Clay Street east from the U.S. 40 Bypass transition into the Mark Twain Expressway (present day Exit 227) to 2nd Street north and the Missouri River Bridge of Highway 115 across the Missouri River. The bridge was closed on December 29, 1992 and demolished in 1997.

Within St. Louis County, the route followed St. Charles Rock Road to a conclusion at Interstate 270 / Exit 20 A, just north of I-70. Toward the end of the 1960s, Business Loop I-70 was redefined to cosign with Missouri 94 east from Exit 228, and 5th Street south from Downtown St. Charles.