I-270 between I-70 and I-55 was formerly designated I-244, a western bypass of St. Louis, Missouri. It was originally proposed by Missouri as I-144, but the road was a beltway (or part of one), so the American Association of State Highway and Transportation Officials (AASHTO) assigned it the number I-244. By the late 1970s, the entire beltway (including today's I-255) was integrated as a part of I-270 for consistency. However, the politicians in Illinois started planning their supplemental freeway system in the mid-1970s and a section of Corridor 413 was included into the Interstate Highway System in April 1978. This caused a potential place of confusion in Pontoon Beach, Illinois, where I-270 would have intersected itself, and eventually the Illinois Department of Transportation (IDOT) decided on the I-255 numbering in 1980 (but not before considering renumbering an section to I-870).