52 BULLETIN 724, U. S. DEPARTMENT (*F AGBICTJLTURE. 
of care exercised in doing the rough grading, and to a less extent on 
the type of road crust or foundation which it is proposed to employ. 
The character of the soil composing the roadbed also may be an im- 
portant consideration in estimating the cost of this work, especially 
if any considerable period of time elapses after the completion of 
the rough grading before the subgrade is prepared. Some soils re- 
main loose indefinitely and are easily worked into proper shape, while 
others may become hard and compact in a very short time after 
being placed in a roadbed. 
The following examples of road-improvement projects completed 
under the supervision of the Bureau of Public Roads have been 
selected to illustrate how the cost of subgrade preparation varies 
with the local conditions, 
Example Xo. 1. — A macadam road in Montgomery County, Md. 
Area surface. 47.456 square yards. 
Character of soil, stiff clay. 
Gradi: g doi e with steam-shovel outfit and not very carefully finished. 
Cost of preparing subgrade. 6.8 cents per square yard. 
Work done with pick and shovels. 
Cost includes necessary rolling. 
Example Xo. 2. — Several sections of gravel road in Leflore County. Miss. : 
Aggregate area surfaced. 189,535 square yards. 
Character of soil, light loam. 
Grading done with scrapers and fairly well finished. 
Cost of preparing subgrade, approximately. 1.4 cents per square yard. 
Work done with road grader and a limited amount of plowing required. 
Cost includes necessary rolling. 
Example Xo. 3. — A gravel road in Bexar County. Tex. 
Area surfaced. 100,000 square yards. 
Work consisted in scarifying and reshaping an old gravel road, and was 
done by means of a roller with scarifier and road grader. 
Cost of preparing subgrade. 3.S cents per square yard. 
Cost includes picking out large stones that were turned up in scarifying, 
as well as all necessary rollings. 
Example Xo. 4. — A concrete road in Licking and Muskingum Counties. Ohio : 
Length of road. 24 miles : width of concrete surface. 16 feet : character of 
soil, stiff clay. The rough grading was done with steam-shovel equipment 
and scrapers, and the work was in progress during 1014 and 1915. During 
1914 the subgrade was prepared almost immediately after the rough grad- 
ing was completed, ano 1 the average cost of its preparation was approxi- 
mately 3 cents per square yard. During 1915 the rough grading was com- 
pleted several months in advance of the subgrade. and the average cost of 
preparing the subgrade was approximately 7.5 cents per square yard. This 
large difference in cost is attributable partly to the fact that several wash- 
ing rains occurred between the time of completing the rough grading and 
the time of preparing the subgrade. and the work charged to subgrade 
preparations really included a considerable amount of rough grading made 
necessary by erosion of the roadbed. 
