Mo. Rev. Stat. § 391.240: Duty of street railway companies where tracks cross railroad tracks.

It shall be the duty of every street railway company or corporation operating a street railway across the tracks of a railroad company to bring its cars to a full stop at least ten and not more than twenty feet before reaching the tracks of the railroad company. And it shall be the duty of the conductor, or some other employee of the street railway company, to go forward to the tracks of such railroad company for the purpose of ascertaining whether a train is approaching such crossing.