ROADS 207 



grade and placing on top of this pavement a layer of broken 

 stone or good gravel, which is thoroughly rolled. This 

 class of road is not used much in the western country at 

 the present time. 



Oiled. The use of rapidly moving motor cars driven by 

 the rear wheels has been found to have a very wearing effect 

 on earth, gravel, and stone roads. The wheels grind the 

 material into a powder, which rises as dust and is blown from 

 the road. As a result the thickness of the road covering 

 is rapidly decreased. To overcome this it is necessary to 

 place over the surface of the finished road a strong binder 



Fig. 183. Cross section of a telford road 



of some nature that will hold the particles together and 

 prevent the formation of a powder which the wind can 

 remove. This is best accomplished by means of a coating 

 of heavy oil, which will penetrate the surface and unite the 

 particles into a solid mass, spread over the road after con- 

 struction or at frequent intervals. Any of the roads above 

 described can be treated with oil and are then known as 

 oiled roads. The success of oiling will depend upon the 

 character of the oil used and the nature of the road cover- 

 ing. Either too large or too small a quantity of oil will 

 not give good results. A thin oil does not furnish a binder 

 of sufficient strength, and a thick oil will not penetrate deep 

 enough to bind firmly. Thick oils are frequently poured 

 when hot in order that their penetrating qualities may be 

 increased. Oiling has not been found very beneficial on 

 clay and loam roads. It gives the best results on good 

 gravel or broken stone. 



Pavements. Country highways as above described have 

 been found fairly satisfactory for horse and light auto- 

 mobile traffic. To secure permanency and low maintenance 

 cost on through roads subjected to the heavy loads and high 



