No municipality having a population of sixty thousand (60,000) persons or more according to the latest Federal Decennial Census shall be required to participate financially in the acquisition of land for use for rights-of-way for state highways contracted for and constructed after the effective date of this section; provided that this section shall not relieve any said municipality of such financial participation where responsibility for the same has been assumed under a preexisting contractual agreement with the department.
Okla. Stat. tit. 69, § 1206.2