With Interstate 144 changed to I-244 since it formed part of a loop, AASHO approved the Interstate Route Numbering for Missouri on November 10, 1958.1
Named the Circumferential Expressway, the quadrant of I-270 between I-55 at Mehlville and I-70 at Champ remained signed as Interstate 244 until 1974. The route was renumbered as an extended I-270 to alleviate motorist confusion.2 The final segment for I-244, Olive Boulevard (Route 340) and I-70, was dedicated on May 20, 1967.3
The same actions approved by the American Association of State Highway and Transportation Officials (AASHTO) on June 25, 1974 to renumber I-244 included the renumbering of I-255 to I-270 as well. The southeast loop changed back to Interstate 255 in 1979. AASHTO approved the redesignation, subject to concurrence from the Federal Highway Administration (FHWA concurrence), on June 25 of that year.
The cloverleaf interchange joining I-255 and I-270 with I-55 at Mehlville was upgraded to a cloverstack interchange from 1991 to 1994. Road construction included building collector distributor roadways along both sides of I-55 north to Lindbergh Boulevard (U.S. 50/67), where a diamond interchange was upgraded to a SPUI. The project addressed a weaving traffic pattern. Work continued through 1997 along I-270, with the beltway expanded northward from I-55 to I-44 to eight overall lanes.3