Idaho Code § 40-1324
When a highway district is organized under the provisions of this chapter, it shall, except as otherwise provided, supersede all other highway districts or parts of districts within the limits of the highway district, and upon the organization the existing position of director of highways shall be abolished. After the organization of a highway district the highway commissioners have the exclusive power to levy and apply all bridge and highway taxes within the district. Where prior to the organization of a highway district bonds shall have been lawfully issued by the county including within its territory property afterward included within the highway district, the proper corporate authorities of the county shall continue to levy, collect and apply the taxes necessary to discharge the obligation of those bonds. Nothing in this chapter shall be construed as affecting any power of any incorporated city, or portion of it, lying within the limits of a highway district, to issue bonds as empowered by law and to levy, collect or apply the necessary taxes for them.
Idaho Code § 40-1324