Idaho Code § 40-1207
Directors of highways, or any other persons legally appointed to take charge of a bridge, may post a notice to set out and provide that no horse or mule-drawn vehicle, nor a person riding a horse or mule shall travel across the bridge or any portion of the bridge faster than at a walk; that horses, mules or cattle shall not be allowed to cross in bunches of more than twenty (20) at a time, and shall not travel faster than at a walk. The notice shall be posted in a conspicuous place and shall be in letters large enough and placed in a manner that it may be easily read by the public. Directors of highways may make other rules and regulations governing the traffic on bridges within their jurisdiction when it is deemed necessary for the safety of the public, and may post a notice of the rules in the manner provided in this section. Any person convicted for violating any of the provisions of a notice as provided for by this section shall be guilty of a misdemeanor, and upon conviction shall be fined not less than ten dollars ($10.00) nor more than three hundred dollars ($300), or may be imprisoned not less than ten (10) days nor more than sixty (60) days in the county jail, or by both fine and imprisonment.
Idaho Code § 40-1207