It is hereby found, determined, and declared that the creation of a joint authority and the carrying out of its corporate purposes is for the benefit of the people of the State of Nebraska, for the improvement of their welfare and prosperity, and for the promotion of their transportation, and is a public purpose and a matter of statewide concern, that aviation projects operated by joint authorities are essential parts of the public transportation system. The State of Nebraska covenants with the holders of such bonds that joint authorities shall be required to pay no taxes or assessments upon any of the property acquired by them or under their respective jurisdictions, control, possession, or supervision to the extent such property is used for a public purpose, or upon the activities of joint authorities in the operation and maintenance of projects, or upon any charges, fees, revenue, or other income received by authorities except motor vehicle fuel and aviation fuel taxes, and that the bonds and notes of joint authorities and the income therefrom shall at all times be exempt from taxation, except for transfer and estate taxes. This section shall constitute a covenant and agreement with the holders of all bonds and notes issued by authorities.