Annually, within sixty (60) days after the close of each fiscal year of any public trust which shall have issued bonds for the construction, operation and/or maintenance of a toll expressway, the trustees of such trust shall pay to the State Treasurer all funds which are not required to be used for other purposes under the terms of the instrument creating the trust and any bond indenture executed in connection with such expressway project, and in such event, such surplus revenue may be appropriated by the Legislature for the benefit of schools or public highways or both.
Okla. Stat. tit. 69, § 3015