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HIGHWAY CONSTRUCTION 



depend altogether on local circumstances. Pavements must be adapt- 

 ed to the class of traffic that will use them. The pavement suitable 

 for a road through an agricultural district will not be suitable for the 

 streets of a manufacturing center; nor will the covering suitable for 

 heavy traffic be suitable for a pleasure drive or for a residential district. 

 General experience indicates the relative fitness of the several 

 materials as follows: 



For country roads, suburban streets, and pleasure drives broken 

 stone. For streets having heavy and constant traffic rectangular 

 blocks of stone, laid on a concrete foundation, with the joints filled 

 with bituminous or Portland cement grout. For streets devoted to 

 retail trade, and where comparative noiselessness is essential asphalt, 

 wood, or brick. 



Desirability, The desirability of a pavement is its possession of 

 qualities which make it satisfactory to the people using and seeing it. 

 Between two pavements alike in cost and durability, people will have 

 preferences arising from the condition of their health, presonal pre- 

 judices, and various other intangible influences, causing them to select 

 one rather than the other in their respective streets. Such selections 

 are often made against the demonstrated economies of the case, and 

 usually in ignorance of them. Whenever one kind of pavement is 

 more economical and satisfactory to use than is any other, there should 

 not be any difference of opinion about securing it, either as a new 

 pavement or in the replacement of an old one. 



The economic desirability of pavements is governed by the ease 

 of movement over them, and is measured by the number of horses or 

 pounds of tractive force required to move a given weight usually one 

 ton over them. The resistance offered to traction by different pave- 

 ments is shown in the following table : 



Resistance to Traction on Different Pavements 



