In the discretion of the parkways authority any bonds issued under the provisions of this article may be secured by a trust agreement by and between the parkways authority and a corporate trustee, which may be any trust company or bank having the powers of a trust company within or without the state. Any such trust agreement may pledge or assign the tolls, rents, fees, charges and other revenues to be received, but shall not convey or mortgage any project or any part thereof. Any such trust agreement or any resolution providing for the issuance of such bonds 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 covenants setting forth the duties of the parkways authority in relation to the acquisition of property and the construction, reconstruction, improvement, maintenance, repair, operation and insurance of the project or projects in connection with which such bonds shall have been authorized, and the custody, safeguarding and application of all moneys, and provisions for the employment of consulting engineers in connection with the construction or operation of such project or projects. It shall be lawful for any bank or trust company incorporated under the laws of the state which may act as depository of the proceeds of bonds or of revenues to furnish such indemnifying bonds, or to pledge such securities as may be required by the parkways authority. Any such trust agreement may set forth the rights and remedies of the bondholders and of the trustee, and may restrict the individual right of action by bondholders as is customary in trust agreements or trust indentures securing bonds and debentures of corporations. In addition to the foregoing, any such trust agreement may contain such other provisions as the parkways authority may deem reasonable and proper for the security of the bondholders. All expenses incurred in carrying out the provisions of any such trust agreement may be treated as a part of the cost of the operation of the project or projects to which the trust agreement applies.