Except as provided in this section, when all bonds issued under the provisions of this chapter in connection with the project and the interest thereon have been paid or a sufficient amount for the payment of all such bonds and the interest thereon to the maturity thereof has been set aside in trust for the benefit of the bondholders, the project, if then in good condition and repair, shall become a part of the primary state highway system and shall thereafter be maintained by the Commonwealth Transportation Board free of tolls. The Commission may, in any resolution or trust indenture authorizing or securing bonds under the provisions of this chapter, provide for combining the project and any public ferry service then being operated by the Commission for financing purposes, and for the continuance of tolls on the project and such public ferry service until all such bonds and the interest thereon have been paid or a sufficient amount for such purposes has been set aside in trust for the benefit of the bondholders.