Okla. Stat. tit. 47, § 47-11-802: Establishment of state speed zones

Whenever the State Highway Commission shall determine upon the

basis of an engineering and traffic investigation that any maximum

speed hereinbefore set forth is greater or less than is reasonable

or safe under the conditions found to exist at any intersection or

other place or upon any part of the state highway system, said

Commission may determine and declare a reasonable and safe maximum

limit thereat which, when appropriate signs giving notice thereof

are erected, shall be effective at all times, or during hours of

daylight or darkness or at such other times as may be determined at

such intersection or other place or part of the highway.