however, at similar volumes 5.1 percent of the vehicle speeds exceeded 60 miles per hour and 36.6 percent exceeded 50 miles per hour. The width of the two-lane road studied was narrower than the 24-foot width recommended for the toll roads, and similar studies on wider two-lane pavements might show a somewhat greater percentage of fast driving, but it is certainly indicated that on any two-lane road speed of operation would be limited to a greater extent than on four-lane divided highways. These figures add to the evidence that even under conditions of light traffic, four-lane divided highways induce higher speed and therefore will prove more attractive to drivers wishing to save time with safety.
The faster travel speeds in themselves indicate a willingness of the driver to pay for saving in time, since increasing speed increases gasoline consumption. Composite figures obtained by averaging the results of tests on several makes of modern passenger cars show that with steady driving on concrete pavements at a speed of 40 miles per hour, gasoline consumption is 0.0575 gallon per mile. At 60 miles per hour the consumption becomes 0.082 gallon per mile. With gasoline at 18 cents per gallon the cost per mile would increase from 1.03 to 1.47 cents per mile, representing a cost for the higher speed of over 0.4 cent per mile for gasoline alone. Should the availability of a large mileage of high-speed highway induce the more general usage of over-drive transmissions, or the introduction of engines performing more efficiently in the higher speed ranges, the final cost of fast driving on toll highways might be no higher than present costs of traveling at similar speeds, desired but seldom possible, on existing highways.
Since the studies of highway capacity are still incomplete, the figures presented are based on data obtained on the best alinement; that is, a level straight highway. Introduction of grades and curves, even of the low magnitude recommended for the selected routes will tend to reduce somewhat the freedom of movement possible. Therefore, in any section of the country where curves and grades must be incorporated frequently in the design of the highway, there will be on two-lane roads a further restriction to the freedom of movement.
It may be thought that differences in speeds will not be significant on such roads since only persons desiring to travel at the highest reasonable speed will be willing to pay the required fees. This might be true with reference to passenger vehicles, even though the data of plates 25 and 26 tend to dispute that thought, but it must be remembered that the value of time and distance saved over such roads will be largest for commercial vehicles. It may be expected that commercial vehicles, particularly the heavier units, would be attracted to these roads in greater proportion than that in which they are found on the existing roads.
FOUR HUNDRED VEHICLES PER HOUR INCONVENIENCE TO IN BOTH DIRECTIONS CAUSE TRAFFIC
Results of studies of the movement of many thousands of vehicles in many sections of the country show that the spacing of vehicles traveling normally over a highway follows rather definite laws. Analysis of observations shows that with a traffic volume of 200 vehicles per hour in one direction, spaces between these vehicles long enough to permit vehicles moving in the opposite direction to pass
