17-5-914. Continuation of taxes -- limit on additional highway revenue bonds. The legislature shall provide for the continued assessment, levy, collection, and deposit of highway revenues into the state special revenue fund for the credit of the department in amounts sufficient to pay, when due, the annual debt service charges on all outstanding highway revenue bonds. The board is authorized to include a contractual undertaking for the benefit of bondholders to this effect in the resolution or indenture under which the bonds are issued.