The object of a road is to provide a way for transportation. It goes without saying, therefore, that its situation should be such that it can perform this function most efficiently, and a system of highways should perform the same function for the public in the same manner. Efficiency here includes the ideas of economy and satisfaction combined. In order to make a layout of a system of highways they should first be classified as to use, for the proper treatment will depend upon the use to which the roads are to be put. Anyone attempting a layout will make his own classification suitable to the inherent conditions pertaining to the district covered. The classification of Mr. T. H. MacDonald, Director of the Bureau of Public Roads, U. S. Department of Agriculture, made for another purpose may be adopted:[174] 1. Those used chiefly related to agriculture. 2. Those which are recreational in character. 3. Those which are commercial. 4. Those which are military. Agricultural roads comprise those leading from farm to town and are used chiefly for marketing, and for social, educational, and religious activities. Recreational roads are either local, upon which driving is done for pleasure, or through, those followed by tourists in traveling over the country. Either of which may lead to places of interest within or without the state. The national park roads and forest highways can be classified under the head of recreational. Commercial highways comprise those exclusive of agricultural, upon which the haul is chiefly of a business nature such as freight and express and bus traffic. The War Department of the United States during the war refused to designate any roads as special Military Highways, saying a road which would adequately serve the agricultural; recreational, and commercial interests would serve the military. However, it might be well to keep in mind this possible use of the highways. A classification of roads into National, State, County and Town has frequently been suggested. Since national roads do not exist as such in the United States the most densely traveled routes and those used largely for through traffic are usually designated state roads, and all others local roads. Keeping the cost and use of the roads in view the problem before the road planner is: (1) To secure the most economical routes in construction and maintenance and future haulage, taking into account topography, alignment, grades, and amount of traffic. (2) To accommodate the greatest number of people commensurate with the money available for expenditure. (3) To utilize existing roads as far as practicable. The system will ordinarily consist of one or more trunk lines to be laid down first and several branch lines connecting with the trunk lines. Some of the essentials to be considered are: