Colo. Rev. Stat. § 43-3-205
In the discretion of the department of transportation, such bonds may be secured by a trust indenture by and between the department of transportation and a corporate trustee which may be any trust company or bank having the powers of a trust company within or outside of the state. Such trust indentures may pledge or assign tolls and revenue to be received from the operation of the turnpike project but shall not convey or mortgage the turnpike or any part thereof. The resolution providing for the issuance of such bonds or such trust indenture may contain such provisions for protecting and enforcing the rights and remedies of the bondholders as may be reasonable and proper and not in violation of law, including, without limiting the generality of the foregoing, covenants setting forth the duties of the department of transportation in relation to the acquisition of properties and the construction, maintenance, operation, repair, and insurance of the turnpike project and the custody, safeguarding, and application of all moneys. Such indenture may set forth the rights and remedies of the bondholders and of the trustee and may restrict the individual right of action of bondholders. In addition to the foregoing, such trust indenture may contain such other provisions as the department of transportation may deem reasonable for the security of bondholders. All expenses incurred in carrying out such trust indenture may be treated as a part of the cost of maintenance, operation, and repair of the turnpike project.
C.R.S. § 43-3-205