Covenant of the state.

The state does hereby pledge to, and agrees with, any person, firm, corporation, or federal or state agency subscribing to or acquiring the bonds to be issued by the agency for the purposes of this act that the state will not limit or alter the rights hereby vested in the agency and the department until all bonds at any time issued, together with the interest thereon, are fully paid and discharged, insofar as the same affects the rights of the holders of bonds issued hereunder. The state does further pledge to, and agrees with, the United States that, in the event any federal agency constructs, or contributes any funds for the completion, extension, or improvement of, an expressway system or any part or portion thereof, the state will not alter or limit the rights and powers of the agency and the department in any manner which would be inconsistent with the continued maintenance and operation of the expressway system or the completion, extension, or improvement thereof or which would be inconsistent with the due performance of any agreement between the agency and any such federal agency, and the agency and the department shall continue to have and may exercise all powers granted so long as the same shall be necessary or desirable for carrying out the purposes of this act and the purposes of the United States in the completion, extension, or improvement of the expressway system or any part or portion thereof.