The Department of Transportation shall construct the highways in the state highway primary system and the highways in the state highway secondary system to standards commensurate with the amount and types of traffic services to be rendered by the highways in the respective systems, it being the declared policy of the State that the highways in the state highway secondary system shall be constructed by less expensive standards than the highways in the state highway primary system, thus enabling the State to construct a larger mileage of all-weather farm-to-market roads from the available funds.