Public Highways 287 



ever, a horse may exert twice his average pulling strength 

 for a few minutes. In the case of a very long hill, it might 

 in some cases be better to make a number of steeper 

 but shorter pulls than to make one long gradual pull,. 

 Thus we see that grades greatly decrease the hauling 

 capacity, and, inasmuch as whatever decreases the 

 hauling capacity correspondingly decreases earning 

 capacity, the importance of reducing grades in road 

 improvement is easily understood. 



407. Effect of Width of Tire on Draft. It is important 

 to know the effect of the width of the tire on the amount 

 of draft required to move a load. The results given in 

 the table (][ 405) are fairly representative. These results 

 and many others indicate that there is no advantage in 

 wide tires on pavements and very hard roads, but for 

 ordinary country hauling the wide tire offers several ad- 

 vantages. Narrow tires are very destructive to road sur- 

 faces, but wide tires roll and harden the surf ace like a roller. 



408. Good Road Essentials. A road should have a 

 smooth, hard surface and a reasonably level grade, and 

 it should have such a foundation that it will maintain 

 its smooth surface in dry as well as wet weather, that is, 

 its essential qualities should be permanent. In building 

 roads, therefore, they should be given such form and con- 

 struction as will maintain these qualities under constant 

 use in varying weather conditions. Drainage is the all- 

 important problem encountered by the road engineer. 

 The road must be so laid out and constructed as to shed 

 water as quickly as possible, to prevent damage, to sur- 

 face and foundation. (Fig. 181.) The surface of the road- 

 bed should be slightly elevated in the middle, so that 

 the rain-water will run immediately to the side ditches 

 before it has time to penetrate into the foundation. 



