56 BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 



The construction method described above is modified quite fre- 

 quently by omitting the subgrade trench and the rolling. The prac- 

 tice followed in many localities is simply to grade up the roadbed and 

 heap gravel along the central portion. Traffic is then depended upon 

 to spread and compact the gravel and produce a uniform surface. 

 While some of the roads constructed in this way are great improve- 

 ments over the original earth roads they nearly always are crowned 

 too much for comfortable driving, and seldom wear as well as when 

 the more careful method of construction is followed. It is believed, 

 therefore, that in the long run it pays to employ a trenched sub- 

 grade and to compact the surface by rolling, though a possible ex- 

 ception to the economy of a trenched subgrade may exist where good 

 gravel may be obtained very cheap. In this case it may be cheaper 

 to surface the entire roadway than to incur the additional expense of 

 trenching and constructing earth shoulders. 



COST OF GRAVEL ROADS. 



In estimating the cost of a gravel road it is necessary to consider 

 (1) the cost of grading and preparing the subgrade, (2) the pur- 

 chase price of the gravel it is proposed to use, (3) the cost of de- 

 livering the gravel on the road, and (4) the cost of spreading and 

 compacting the gravel. 



The cost of grading has been discussed in connection with earth 

 roads and need not be considered here. But it should be borne 

 in mind that the cost of preparing the subgrade, after the rough 

 grading is complete, depends to a very considerable extent upon the 

 degree of care exercised in doing the latter work. The character of 

 the soil composing the roadbed also may be an important factor in 

 determining the cost of preparing the subgrade, especially if any 

 considerable period of time elapses after the completion of the rough 

 grading before the subgrade is prepared. Some soils remain loose 

 indefinitely and are worked into proper shape easily, while others 

 may become hard and compact in a very short time after being placed 

 in a roadbed. 



Where a road has been graded previously with moderate care and 

 has not settled out of shape or been allowed to erode, and where the 

 price of labor is about 20 cents per hour and of teams about 40 cents 

 per hour, the cost of preparing a subgrade for a gravel road sur- 

 face varies about as follows: 



Cents 



per square 



yard. 



Light loam soil 1| to 2 



Light clay soil, freshly graded 2 to 4 



Stiff elay soil, freshly graded 3 to 5 



Stiff clay soil, thoroughly compacted 5 to 8 



