The Parkways Authority is hereby authorized to provide by resolution for the issuance of parkway revenue refunding bonds of the state for the purpose of refunding any bonds then outstanding which shall have been issued or may be issued under the provisions of this article in connection with the construction of any parkway project, including the payment of any redemption premium thereon and any interest accrued or to accrue to the date of redemption of such bonds; and, if deemed advisable by the Parkways Authority, for the additional purpose of constructing improvements, extensions or enlargements of the project or projects in connection with which the bonds to be refunded shall have been issued: Provided, That this section shall not be construed as authorizing the issuance of parkway revenue refunding bonds for the purpose of refunding any bonds then outstanding which shall have been issued under the provisions of this article, or any predecessor thereof, in connection with the construction of the West Virginia Turnpike, which revenue refunding bonds may be issued only as authorized under section twenty-two of this article. The issuance of such bonds, the maturities and other details thereof, the rights of the holders thereof and the rights, duties and obligations of the Parkways Authority in respect of the same shall be governed by the provisions of this article insofar as the same may be applicable. No issuance of a refunding bond may extend the maturity date of such bond being refunded and may not exceed the outstanding principal of such bond being refunded. Any refunding bond shall be structured to provide for approximately level annual debt service savings each fiscal year through the final maturity or structured to approximate the level of debt service that would have been paid prior to the refunding, with a preponderance of the savings being deferred toward eliminating or reducing the most distant maturities. For purposes of this section, the outstanding principal is to be determined as of the date on which the revenue bond is refinanced.