It is hereby found, determined, and declared that there exists a need for the construction of highways in this state requiring the issuance of bonds by the commission acting for and on behalf of the state, all as more fully provided in the Nebraska Highway Bond Act, that the creation of the commission and the carrying out of its purpose are in all respects for the benefit of the people of this state and for the improvement of their health, welfare, and prosperity and constitute a public purpose, and that such bonds, the interest thereon, and the income therefrom shall at all times be exempt from taxation by this state or any political subdivision of this state.