Interstate 370 currently does not exist in Missouri. Although Missouri 370 is a freeway, it was constructed without Interstate funding, so it is likely to remain a state route. However, no official plans currently exist to convert Missouri 370 into Interstate 370.4
Missouri 370 is the 12-mile freeway connecting Interstate 270 with Interstate 70 in the vicinity of St. Charles, northwest of St. Louis. When the first segment between Missouri 94 and Interstate 270 was opened in late 1992, the route was designated as Missouri 115. It was subsequently redesignated as Missouri 370 in early 1993. By 1997, maps show that Missouri 370 was complete west to Interstate 70.
According to Interstate 370 at Kurumi.com (Scott Oglesby), Missouri 370 was considered to become Interstate 370, but it would only be approved by the American Association of State Highway and Transportation Officials (AASHTO) if it were renumbered as Interstate 870.12 Missouri did not want to do this, because Interstate 870 is a designation that is supposedly (per Brian Dowd, a resident of St. Louis who is familiar with highways in the area) being reserved for a bypass route in Columbia.3 As a result, the Missouri Department of Transportation opted to retain the 370 designation for the route and left it as a state route. The Interstate designation may still occur if an agreement can be reached on the designation between the two agencies, but for now, this is Missouri 370.
Missouri 370 was originally planned as Missouri 115, but it was renumbered to be consistent with the numbering of Interstate 70 and Interstate 270. Here is a brief chronology of the freeway:5
August 3, 1984 - Missouri 115 (370) preliminary alignment adopted by the Missouri Highways and Transportation Commission for section from Interstate 270 to Missouri 94
1985 - Highway 115 Northern Corridor Commission formed to promote the development of the new freeway
April 1987 - gasoline tax approved by voters; funds used for Missouri 370 extension from Missouri 94 to Interstate 70
December 1988 - Construction began with new interchange at Interstate 270
December 16, 1992 - Discovery Bridge and first leg of Missouri 370 opens ahead of schedule at a ribbon-cutting ceremony
1997 - remaining section from St. Charles to St. Peters opens; old Missouri 115 bridge demolished
Westbound Interstate 70 approaches its junction with Missouri 370 at Exit 224, one mile. Photo taken 10/16/04.
Westbound Interstate 70 approaches the Missouri 370 freeway in one-half mile. In this direction, the offramp only has one lane. Along eastbound, more lanes are allocated for the connection to Missouri 370 eastbound. Photo taken 10/16/04.
Westbound Interstate 70 reaches its junction with Missouri 370. Photo taken 10/16/04.