Mo. Rev. Stat. § 307.190

Every person operating a bicycle or motorized bicycle at less than the posted speed or slower than the flow of traffic upon a street or highway shall ride as near to the right side of the roadway as safe, exercising due care when passing a standing vehicle or one proceeding in the same direction, except when making a left turn, when avoiding hazardous conditions, when the lane is too narrow to share with another vehicle, or when on a one-way street. Bicyclists may ride abreast when not impeding other vehicles.