ROADS AND BRIDGES 



313 



the broad drains which form the roadside ditches. In 

 other cases, as in the semi-arid regions of the central 

 West, only a single team path or narrow roadway, 

 rounded up with the reversible machine, making shallow 

 side ditches, is all that is required because teams can 

 easily turn out on either side on the solid earth. 



In prominent roads, the important subject to be taken 

 into consideration in deciding upon the width is the kind 

 of surfacing material which will be used later on and its 

 position on the crown of the road, whether on the cen- 

 ter or at one side of the center. These materials are 

 expensive and are usually laid from 9 to 16 feet wide, 

 though wider on very prominent roads. 



ECONOMIC HANDLING OF EARTH 



In no part of road making has machinery been so well 

 developed for saving labor and for making possible im- 

 proved roads, as in carry- 

 ing dirt from roadside 

 ditches to the rounded 

 roadbed in making the 



COUntrV dirt road. Peaty land. The clay layer, O, is only a foot 

 J thick, and is covered with 8 inches of gravel. 



road ma- This grade is not too heavy, and has a stiff 

 bottom zone, which will not be crushed into 



chine is by far the most the peat - as ln Figure m - 

 important machine in road' building. The elevating grader 

 is also a very important invention, and when large 

 amounts of earth are to be taken from ditches on either 

 side of the road and built up into an embankment it is 



very useful. While the 



greater adaptability of the 

 reversible machine makes 

 it better for lighter grad- 

 ing, the less cost per cubic 

 yard of earth handled, 



olid "in some "cases caus^lT'to" ooze"out "and where tllC grade S are 

 :>ulge up, as at M, displacing and even f 



Figure 196. Cross-section of a grade across 



Figure 197. Heavy grade built across a 

 marsh. The weight compresses the peat at K, 



