332 THE POPULAR SCIENCE MONTHLY 



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 un- 

 pleasant 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 photograplis 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 con- 

 structed 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 ^tate 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 Massachu- 

 setts Highway Association, stated that 



Up to the year 1907 the cost per mile for maintenance of the Massachusetts 

 state highways was not far from $100. 



