Except as otherwise provided in RCW *
47.56.291, **
47.56.714, and *
47.56.756, as long as any of the bonds issued hereunder for the construction of any toll bridge are outstanding and unpaid, there shall not be erected, constructed, or maintained any other bridge or other crossing over, under, through, or across the waters over which such toll bridge is located or constructed, connecting or joining directly or indirectly the lands or extensions thereof or abutments thereon on both sides of the waters spanned or crossed by such toll bridge within a distance of ten miles from either side of such toll bridge excepting bridges or other highway crossings actually in existence and being maintained, or for which there was outstanding an existing and lawfully issued franchise, at the time of the location of such toll bridge and prior to the time of the authorization of such bonds, and no ferry or other similar means of crossing the said waters within the said distance and connecting or plying directly or indirectly between the lands or extensions thereof or abutments thereon on both sides of the waters spanned or crossed by such bridge shall be maintained or operated or permitted or allowed: PROVIDED, That ferries and other similar means of crossing actually in existence and being maintained and operated, or for which there was outstanding an existing and lawfully issued franchise, at the time of the location of such bridge and prior to the time of the authorization of such bonds, may continue and be permitted to be operated and maintained under such existing rights and franchises, or any lawful renewal or extension thereof. The provisions of this section shall be binding upon the state department of transportation, the state of Washington, and all of its departments, agencies, or instrumentalities as well as any and all private, political, municipal, and public corporations and subdivisions, including cities, counties, and other political subdivisions, and the prohibitions of this section shall restrict and limit the powers of the legislature of the state of Washington in respect to the matters herein mentioned as long as any of such bonds are outstanding and unpaid and shall be deemed to constitute a contract to that effect for the benefit of the holders of all such bonds.