(1)(a) Subject to subsection (2) of this section the secretary may increase the maximum speed limit on any highway or portion thereof to not more than seventy-five miles per hour in accordance with the design speed thereof (taking into account all safety elements included therein), or whenever the secretary determines upon the basis of an engineering and traffic investigation that such greater speed is reasonable and safe under the circumstances existing on such part of the highway.

(b) The greater maximum limit established under (a) of this subsection shall be effective when appropriate signs giving notice thereof are erected, or if a maximum limit is established for auto stages which is lower than the limit for automobiles, the auto stage speed limit shall become effective thirty days after written notice thereof is mailed in the manner provided in subsection (4) of this section.

(c) Such maximum speed limit may be declared to be effective at all times or at such times as are indicated upon said signs or in the case of auto stages, as indicated in said written notice; and differing limits may be established for different times of day, different types of vehicles, varying weather conditions, and other factors bearing on safe speeds, which shall be effective when posted upon appropriate fixed or variable signs or if a maximum limit is established for auto stages which is lower than the limit for automobiles, the auto stage speed limit shall become effective thirty days after written notice thereof is mailed in the manner provided in subsection (4) of this section.

(2) The maximum speed limit for vehicles over ten thousand pounds gross weight and vehicles in combination except auto stages shall not exceed sixty miles per hour and may be established at a lower limit by the secretary as provided in RCW 46.61.405.

(3) The word "trucks" used by the department on signs giving notice of maximum speed limits means vehicles over ten thousand pounds gross weight and all vehicles in combination except auto stages.

(4) Whenever the secretary establishes maximum speed limits for auto stages lower than the maximum limits for automobiles, the secretary shall cause to be mailed notice thereof to each auto transportation company holding a certificate of public convenience and necessity issued by the Washington utilities and transportation commission. The notice shall be mailed to the chief place of business within the state of Washington of each auto transportation company or if none then its chief place of business without the state of Washington.

Intent—1987 c 397: "It is the intent of the legislature to increase the speed limit to sixty-five miles per hour on those portions of the rural interstate highway system where the increase would be safe and reasonable and is allowed by federal law. It is also the intent of the legislature that the sixty-five miles per hour speed limit be strictly enforced." [ 1987 c 397 s 1.]

Federal requirements—1977 ex.s. c 151: See RCW 47.98.070.