.U4 FORMS OK ENERGY character and properties of the soils, the amount of rainfall, and other factors are considered. Experiments show that an ideal grade should not be more than 3 per cent, i.e., a rise of 3 feet in 100 feet of road, and that curves should not be more than 3 degrees, i.e., 3 degrees in 100 feet, thus permitting the driver to see far enough ahead to stop for an obstruction when driving at 70 miles per hour. Fig. 144. U. S. 1 between Richmond and Washington in 1919. (Courtesy of the Public Roads Administration.) Automobile Transportation Has Changed Every Phase of Living. The popular acceptance of the automobile created the demand for good roads, for which the gasoline taxes paid. As a result the country has been criss-crossed with highways; and filling-stations, lunchrooms, and tourist camps have sprung up like mushrooms. Much of the increased leisure afforded by the machine age has been used in touring and holiday driving. Country people have visited the amusement places of the city, and city people have gone to the country for outings. Golf courses, bathing beaches, camping in the mountains, visits to national parks, and tours of the whole country have come within the reach of the' masses. At least 25 per cent of automobile trips are devoted to recreation as reported by the Automobile Manufacturers Association in a survey covering 3,400,000 motorists. The
THE AUTOMOBILE 345 same survey showed 45 per cent of the car miles were for recreational and social uses. Perhaps nothing has done more in leveling the classes in the United States, because the masses are able to enjoy the use of the same highways, city streets, and national parks that the rich man can. Fig. 145. A modern mountain highway. U. S. 99 in Los Angeles County, California. (Official photograph of the California Division of Highways.) The Cost of Operating Early Automobiles Was Very High. In 1911 a Ford touring-car could be purchased for $780; but in spite of this fact, automobiles were restricted to the wealthy because their cost of operation was so high — over 10 cents per mile. New tires cost over twice as much as they do today and lasted less than 1/5 as long. New parts were higher in price and were needed more often. The Plaything of the Wealthy Has Become a Necessity of the Masses. There were few paved highways; and one had to contend with clouds of dust, rough roads, sharp turns, and mud whenever it rained.