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 fact that a macadam road will not withstand such travel (motor vehicles) was again demonstrated upon the piece of road that was built in Becket in 1909, around Jacob's Ladder, so called, where the commission constructed a long stretch of macadam road, using the best local stone available. The road was not open to travel until late in the fall of 1909, but before the first of July, 1910, the surface of the road had been torn up in many places by automobiles, and on the corners and curves deep ruts had formed. Consequently, when the road was less than a year old the commission was obliged to spend over $1,400 a mile in repairing it, putting it back into shape and applying a coat of asphaltic oil. When it is remembered that this road is in a sparsely settled country district, merely part of the main line between the Connecticut Valley and Berkshire County, and that nevertheless there is sufficient automobile travel to make oiling it an absolute necessity for its preservation before it has been used one year, it will be realized that some such treatment of macadam roads will have to be adopted over a large percentage of the state highways in the commonwealth. This treatment costs all the way from $500 to $1,200 a mile, according to the width coated, the length of haul, material available and the class and character of the bituminous binder that it is necessary or advisable to use.
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
