Idaho Code § 49-1005
Whenever in the judgment of the board or authorities in charge of, or having jurisdiction over a highway, the operation on any highway or section of highway of vehicles of sizes and weights at rates of speed permissible by law which will cause damage to the highway by reason of climatic or other conditions, or will interfere with the safe and efficient use of the highway by the traveling public, the board or other authorities in charge of, or having jurisdiction over a highway have authority to make regulations reducing the permissible sizes, weights or speeds of vehicles operated on that highway for any periods as may be necessary for the protection of the highway or for public safety. Signs designating those regulations shall be erected and maintained at each end of the highway or section and at intersections with main traveled highways.
Idaho Code § 49-1005