Idaho Code § 40-816
A highway district board, or other officers of the highway district, shall have no power to incur any debt or liability whatever, either by issuing bonds or otherwise, in excess of the express provisions of this title. Any debt or liability incurred in excess of the express provisions shall be and remain absolutely void. For the purpose of organization or for any of the purposes of this title, a highway district board may, before making the tax levy in any year, incur an indebtedness not exceeding in the aggregate a sum equal to one-tenth per cent (.1%) of the market value for assessment purposes of all the property in the highway district subject to taxation. After making the levy, they may incur an indebtedness within the limit, on the entire indebtedness, of the amount of the levy. At no time shall the total indebtedness exceed that amount and may cause warrants of the highway district to be issued, bearing interest to be fixed by the highway district. The power granted in this section is in addition to and independent of the power granted to issue bonds.
Idaho Code § 40-816