(8) Bridges, culverts, and railroad crossings should, preferably, be directly along the highway and at right angles to the obstruction.

(9) Ruling grades, dependent upon the class of road will also affect the layout.

(10) Esthetics. Perhaps the people of the United States have been too materialistic and have paid too little attention to the beauty and interest elements in highway location. Especially for pleasure riding and recreation should the esthetic side be considered.

Motor Transport Efficiency Outline.

—At this point it would be well for the road planner to consult an excellent paper by M. C. Horine and his efficiency chart which is substantially as follows:[175]

The Highway System Unit.

—Ordinarily the units will be the same as the political divisions, that is, national, state, or local. A national system would include the whole United States and will comprise trunk lines paralleling each other across the country east and west and north and south, considering, of course, ruling points, with a few branch lines of importance. The total number of miles of such highways should probably never exceed 2 per cent of the total mileage in the United States, or about 50,000 miles. A national highway committee estimated that this mileage of roads would serve 87 per cent of the people. The arguments made in favor of a national system of highways may be briefly summarized as follows:

(1) Political lines would be obliterated, thus welding together and unifying all the people. Commercial and social intercourse would wipe out sectional differences, hatreds, and enmities. The people of one section would learn that the people of another section are human beings as they themselves are, and are actuated by the same instincts and inspirations.

(2) Economic, commercial, and pleasure routes cut across state lines and it would be much better to have the roads continuous and administered by one central control. They would then be kept in a more uniform condition of usefulness. The roads radiating from New York City are mentioned as an example. They pass out of the state of New York and into the states of Connecticut, Rhode Island, Massachusetts, New Jersey, Pennsylvania, Delaware, Maryland, and the District of Columbia. On any one of these roads it would be difficult to say which state you are in by observing the license tags on the trucks and automobiles. A Connecticut traffic census on a road carrying approximately 3000 passenger cars and 500 trucks per day showed that 47 per cent of the cars in the analysis came from without the state.