Construction on Route 370 began in the early 1990s . It was built to replace the section of St. Charles Rock Road , then designated as Route 115 , west of Interstate 270 . Route 370 was considered to be Interstate 370 but AASHTO would only allow it if it was renumbered Interstate 870 . MODOT did not want this because the designation of Interstate 870 was for the new southern freeway which is now designated as Interstate 255 . On December 16 , 1992 , the first section of the highway opened allowing direct access to St. Charles at Route 94 from I-270 . It replaced the crumbling Old St. Charles Bridge that carried Route 115 traffic . On April 1 , 1993 , the road was designated as Route 370 . In 1993 , the Great Flood of 1993 surrounded much of the highway which is built on top of an embankment . As the flood waters surrounded the highway , many of the new exits had been shut down because the roads it connected to were underwater . Despite the flood , construction resumed on the highway until it was completed in 1996
Great Flood of 1993
Great Flood of 1993
Missouri Route 370