an interchange with Collinsville Road (formerly US 40) just east of the Fairmont Park Racetrack. I-255 meets I-55/I-70 at an interchange in Collinsville, its original intended terminus. North of this interchange, the control city for I-255 changes from "Chicago" to "To I-270". In the 1980s, I-255 was extended approximately north to meet I-270 in Pontoon Beach, its current terminus. While the I-255 designation ends at the I-270 interchange, the freeway continues north and west (parallelling the bend in the Mississippi River) for approximately as IL 255. The decision to not extend the I-255 designation to the new freeway reflects the fact that state and not federal funds were used to pay for construction. History I-255 route was proposed from I-55/I-244 near Green Park to I-55/70 west of Cahokia Mounds near the intersection with IL 111 when plans surfaced in the 1950s Yellow Book. It was originally designed to be a four lane highway but was changed to six lanes. Since that routing was to go through the American Bottoms, archaeological investigations had to be conducted prior to any construction, which would later become known as the FAI 270 Series. When Cahokia Mounds was designated in the federal register, an alternative alignment for I-255 from I-64 to I-55/70 was selected. This delayed construction of I-255 until the late 1970s, making it the last Interstate Highway in metropolitan St. Louis to be built. Both the western (I-270) and eastern (I-255) portions of the Interstate loop around St. Louis were originally designated as I-270. However, the route that Illinois selected ("Corridor 413") included an interchange in Pontoon Beach between the new beltway (running north and south parallel to the Mississippi River) and the existing beltway (running east and west to a terminus at I-55/I-70). As such, two intersecting Interstate Highways would have carried the same route number. As such, the Illinois Department of Transportation (IDOT) concluded a different route number would be necessary for the eastern leg of the beltway. While I-870 was initially considered, informal use of I-255 in contemporary local media coverage led to its widespread adoption. By 1980, IDOT announced that the eastern portion of the St. Louis beltway was to be designated as I-255. Exit list References External links 55-2 2 55-2 55-2 Roads in Greater St. Louis Transportation in Madison County, Illinois Transportation in Monroe County, Illinois Transportation in St. Clair County, Illinois Transportation in St. Louis County,