Man's physical universe



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

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