Mont. Code Ann. § 17-5-912

All or any portion of highway revenues may be pledged to the payment of the principal, interest, and redemption premium, if any, on particular issues of state highway revenue bonds, and the pledge is and remains at all times a first lien and prior charge upon the pledged highway revenues credited to the highway revenue bond debt service account, subject to the pledge of particular highway revenues to secure particular issues of highway revenue bonds.