After all bonds issued pursuant to this chapter for the construction of the toll tunnel have been fully redeemed and paid, the authority shall either:
(a) Transfer the toll tunnel to the state for operation and maintenance as a state highway by the department, either free of tolls or at the rates of tolls adjusted so as to provide a fund of not to exceed the amount necessary for the proper maintenance, repair, and operation of the toll tunnel under economical management; or
(b) Operate and maintain the toll tunnel itself, either free of tolls or at rates of toll adjusted so as to provide a fund of not to exceed the amount necessary for the proper maintenance, repair, and operation of the toll tunnel under economical management.