EARTH, SAND-CLAY, AND GRAVEL ROADS. 57 



•These costs include all necessary rolling for compacting the sub- 

 gracle. 



The two succeeding factors, purchase price of gravel and cost of 

 delivering the gravel on the road, evidently are dependent to a very 

 great extent on local conditions, and their influence on the cost of a 

 given road can not be determined except by a study of those condi- 

 tions. The following data are intended to serve only as an aid in 

 making the necessary study. 



(a) A cubic yard of loose gravel ordinarily weighs between 2,700 

 pounds and 3,300 pounds, the average weight being about 3,000 

 pounds. 



(b) Loose gravel will shrink from 20 per cent to 30 per cent in 

 volume when compacted in a road surface. In determining the loose 

 volume of gravel required for a* given project, it is customary to 

 compute the compacted volume and add at least one-third. 



(c) The average cost of loading pit gravel by hand into wagons is 

 about 20 cents per cubic yard. Where the amount of work to be done 

 is sufficient to warrant the installation of a steam shovel or the con- 

 struction of a special scaffold so that wheeled scrapers may be used 

 for loading, the cost of this work may be reduced, sometimes 50 per 

 cent or more. 



(d) The cost of screening gravel varies greatly according to the 

 character of the pit-run material and the kind of screening equip- 

 ment employed. Hand screening usually costs from 25 cents to 48 

 cents per cubic yard, while with a properly arranged mechanical 

 screen the cost should not often exceed 15 to 20 cents per cubic yard. 



(e) The cost of hauling depends on the equipment used and the 

 condition of the road over which the hauling is done. With teams 

 at 50 cents per hour and the roads such that 2 tons may be hauled 

 at a load the average cost for hauling is about 25 cents per ton-mile, 

 or 37^ cents per cubicyard-mile. 



The fourth factor to consider, cost of spreading and compacting 

 the gravel, depends on the character of the gravel and of the equip- 

 ment, as well as on the cost of labor. On five gravel-road projects 

 recently completed under the supervision of the Office of Public 

 Roads and Rural Engineering the cost of spreading the gravel 

 ranged from about 3 cents to about 8 cents per cubic yard. The 

 average cost was about 6^ cents per cubic yard, and the average cost 

 of labor was about 20 cents per hour. The wagons used in all cases 

 were dumped directly upon the subgrade and were designed to spread 

 the material to a considerable extent while it was being dumped. 



The cost of rolling the gravel on the above five projects ranged 

 from slightly less than \ cent per square yard of surface to about 1 

 cent per square yard, and the average cost was about 0.6 cent 



