ROADS 163 



packed over the entire width of the road, the upper courses 

 may be applied. This consists of fragments of stone which 

 vary in diameter from 1J^ to 1J/2 inches. After being 

 spread in a manner similar to that described for the lower 

 course, the layer of binding material, which usually con- 

 sists of stone screenings and dust, is applied. This is usually 

 about 1 inch in thickness and it is washed down into the 

 crevices between the stone as much as possible by sprinkling. 

 Rolling is continued until the water that is applied in 

 sprinkling remains on the surface. No more binding 

 material should be used than is necessary, and care should 

 be used to leave the surface of the road as smooth and in as 

 perfect condition as possible. After rolling and bringing 

 the surface into proper condition, the embankments at the 

 sides should be thoroughly rolled smooth so that there will 

 not be any unevenness existing between the stone and the 

 side ditches. 



Bituminous Macadam Roads. The construction which 

 has just been described has been the standard method of 

 stone road construction for many years, but owing to a 

 change 01 traffic other forms of construction have come 

 into use, and this construction is sometimes designated as 

 "water-bound macadam roads." It has proved to be 

 highly satisfactory for the main traveled country road, 

 where first-class roads are desired and where the traffic 

 is limited to horse-drawn vehicles. The automobile, how- 

 ever, has introduced a new problem in connection with road 

 construction. The automobile traveling at a high speed 

 with its broad pneumatic tire sucks out from between the 

 stone fragments the dust which forms the binding material, 

 and causes the stone to loosen, or "ravel," as it is some- 

 times described. So extensive has the motor traffic become 

 in certain localities, that not only must steps be taken to 



