There is created a state design standards committee of seven members, six of which shall be appointed by the executive committee of the Washington state association of counties to hold office at its pleasure and the seventh to be the state aid engineer for the department of transportation. The members to be appointed by the executive committee of the Washington state association of counties shall be restricted to the membership of such association or to those holding the office and/or performing the functions of county engineer in any of the several counties of the state.