Transportation bonds issued by the state transportation commission are securities in which public officers and public bodies of this state and its political subdivisions and insurance companies, trust companies, banking associations, investment companies, executors, administrators, trustees and other fiduciaries may properly and legally invest funds, including capital in their control or belonging to them. The bonds are securities that may properly and legally be deposited with and be received by a state or political subdivision officer for which the deposit of bonds or obligations of the state is authorized by law. Bonds shall not be eligible for investment or deposit by or with the state or its political subdivisions unless they have been rated AA or higher by an independent nationally recognized bond rating service based solely on the security of the bonds as an investment without resort to a collateral guarantee.