As a part of the agreement, the department may assume responsibility for the operation and maintenance and future improvement of the highway. The agreement may also reserve to the governing authority for the Indian peoples of the Quinault Indian Reservation authority to construct public road intersections or grade separation crossings of the highway. Existing rights of access from adjoining property to existing state route number 109 from the south reservation boundary to the township line shall not be affected by RCW 47.20.710 through 47.20.735 or the agreement authorized by RCW 47.20.710.