Mont. Code Ann. § 17-5-913

The board may issue and sell highway revenue bonds to finance the cost of highway projects, to pay the costs of issuing the bonds, and to provide for reserves, upon recommendation of the department. The state reserves the right to issue additional bonds secured equally and ratably by the pledge and appropriation of the highway revenues or separately secured by a portion of highway revenues subject only to the pledge of particular highway revenues to secure particular bonds.