Okla. Stat. tit. 69 § 659
The Department of Transportation is hereby authorized to develop a complete set of county bridge standards, including standards for demonstration bridge projects and standards for county bridges with low average daily traffic volumes as defined by the latest published version of the County Roads Design Guidelines Manual. Such standards shall be developed under the direction of the Bridge Division of the Department and prior to implementation shall be approved by the Oklahoma Cooperative Circuit Engineering Districts Board and the Transportation Commission. Such standards shall be furnished without cost to local units of government. Monies received by the county pursuant to the County Bridge and Road Improvement Act, Section 657 et seq. of this title, may be used for purposes of obtaining engineering services. Only registered professional engineers, approved by the Department, experienced in the design and construction of highway and related facilities, shall be used for such services. Counties acquiring engineering services as provided for in this section shall require the engineers providing such services to execute professional service contracts which include a requirement that the engineer shall maintain an adequate policy of professional liability insurance.
Okla. Stat. tit. 69, § 659