The Doors reference the "blue
bus" in their song, "The End." Other definitions in this site mention that oxycontin may have been referred to as "blue
bus" or that it was a reference to the mentally disabled. While it is possible that the first reference has some significance, the second is obviously wrong.
More likely, however, is that this is a direct and literal (not metaphoric) reference to Santa Monica's "Big Blue
Bus" system which serves the area of Western
Los Angeles, including Jim Morrison's Venice Beach. The Doors were fond of references to LA and it is not surprising that this reference to a
local public transit system would go unnoticed and appear confusing to fans outside the area.