Mo. Rev. Stat. § 389.990

A bell shall be placed on each locomotive engine, and be rung at a distance of at least eighty rods from the place where the railroad shall cross any traveled public road or street, and be kept ringing until it shall have crossed such road or street, or a horn or whistle shall be attached to such engine and be sounded at least eighty rods from the place where the railroad shall cross any such road or street, except in cities, and be sounded at intervals until it shall have crossed such road or street, under a penalty of twenty dollars for every neglect of the provisions of this section, to be paid by the corporation owning the railroad, to be sued for by the prosecuting or circuit attorney of the proper circuit, within ten days after such penalty was incurred, one-half thereof to go to the informer and the other half to the county; and said corporation shall also be liable for all damages which any person may hereafter sustain at such crossing when such bell shall not be rung or such horn or whistle sounded as required by this section; provided, however, that nothing herein contained shall preclude the corporation sued from showing that the failure to ring such bell or sound such horn or whistle was not the cause of such injury.