In December 2003, Scott Maness found what may be the only
supplemental route BA in Missouri. The route designation
resulted from the relocation of Missouri 109 in St. Louis County
near Babler State Park. Missouri 109 formerly went into Babler
State Park. Now, Route BA goes into the park instead. Missouri 109
was re-routed along the former Route C (Eatherton Road).
An examination of two maps, the 2001-2002 official Missouri state map and the AAA Metro St. Louis map published by in 2000 indicates that the realignment occurred in 2000. Route BA was not shown on the 2001-2002 official state map. Instead, the coloration of the routes on the St. Louis metropolitan-area inset map indicated that Missouri 109 runs into the park and along Eatherton Road (its present route). The official 2005-2006 state map is the first official state map that does show Route BA going into Babler State Park. Missouri 109 still ends at Route CC (Wild Horse Creek Road) where Eatherton Road crosses Route CC.
Also note the unusual END and cardinal-direct banners on the sign. In the past couple of years, Missouri has increasingly been using these banners for supplemental routes. Such usage had been rare.