605 ILCS 10/21
When all bonds including refunding bonds and all interest thereon have been paid, or a sufficient amount for the payment of all bonds and interest due or accrued thereon has been set aside in trust for the benefit of the bondholders and shall continue to be held for that purpose, and when all money appropriated by the General Assembly has been repaid as provided by Section 18 of this Act, the toll highways and any connecting tunnels, bridges, approaches or other appurtenances to such toll highways shall become a part of the system of the State highways of the State of Illinois, and be maintained and operated free of tolls.
When all the obligations and all bonds including refunding bonds of the Authority have been paid, or the payment therefor has been provided as is required herein, the Authority shall be dissolved and all funds of the Authority not required for the payment of bonds, interest, machinery, equipment, property or other obligations of the Authority shall be paid to the State Treasurer.
605 ILCS 10/21