EARTH, SAND-CLAY, AND GRAVEL ROADS. 57 
These costs include all necessary rolling for compacting the sub- 
* grade. 
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. 
(h) 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 6J 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 
