the surface. This fine material in its loosened condition is picked up by the current of air produced by the rapid motion of the car and is blown away, forming the clouds of dust which is one of the most unpleasant features of the use of motor cars. Of course the greater the speed the greater the shearing action of the tires, the greater the amount of dust loosened and the greater the destruction of the road. As a matter of fact there is little or no damage done at speeds of less than thirty miles an hour. That the damage is due to the rear wheels alone is shown in instantaneous photographs of a car moving at ninety miles an hour over a water-bound surface. Practically no dust is to be seen about the front wheels while a cloud arises from-the rear tires. If the commonly accepted theory that the destruction of the road surface is due to the suction of the rubber tires, there should be an equal amount of dust stirred up by both the rear and front wheels.
The present condition of affairs is still further illustrated by the statement of the Massachusetts Highway Commission in its 18th annual report for the fiscal year ending November 30, 1910, which follows:
The strongest evidence of the fact that motor travel has injured roads of the water-bound broken-stone type is the increase in the cost of their maintenance, both in this country and abroad, since they have been used by automobiles, in regard to which a few data, among the large number available, are of interest.
At a conference of the governors and chief highway officials of the New England states, called together at Boston by Governor Guild, of Massachusetts, in 1909, Mr. Harold Parker, chairman of the Massachusetts Highway Association, stated that