10 



BULLETIN 136, U. S. DEPARTMENT OF AGRICULTURE. 



of the adjacent land. On each of the six radial market roads which 

 have been assumed for the calculations above there would be a traffic 

 area of 4,021 acres and a farm area of 2,614 acres per mile. 



COST OF HIGHWAY CONSTRUCTION. 



The cost of a given type of highway varies, but the range of variation 

 has become comparatively well defined for each type within a given 

 region. The standard of construction for any given type is now also 

 generally understood and adhered to in the best practice. As this 

 standard becomes more generally adopted, the price variation for 

 similar local conditions will become less. In Table 5 there are given 

 examples of cost per mile for three types of modern State highways. 

 These averages are taken from lists of State construction jobs which 

 are tabulated in Appendix C. 1 The standard which present specifica- 

 tions represent is a necessary standard evolved as the result of 20 

 years of modern road building. When these standards are ignored, 

 it is usually at the expense of good work. 



Table 5. — Cost elements of three types of highways. 1 



Type. 



Drainage 



and 

 grading. 



Surfacing. 



Total. 



Drainage 



and Surfacing, 

 grading. 





81, 817 

 3,400 

 2,765 



$2, 599 

 5,815 

 7,533 



$4, 416 

 9,215 

 10,298 



Per cent. Per cent. 

 41.15 | 58.85 



Ordinary or water-bound macadam (15 feet wide). 



36.90 63.10 

 26.85 73.15 







1 These cost elements were obtained from 87 gravel jobs and 104 macadam jobs in Maine and New Jersey, 

 and from 53 bituminous-macadam jobs in Maine, Massachusetts, and New Jersey. The averages were 

 computed by weighing each job with its relative length and reducing all costs by simple proportion to 

 equivalent average widths of 20 feet and 15 feet respectively. The complete tables of cost elements on the 

 244 jobs are given in Appendix C 



2 Includes eight jobs of bituminous resurfacing. (See footnotes, Appendix C.) 



The cost of highway construction may be subdivided into (a) cost 

 of enduring features and (b) cost of perishable features. When roads 

 are built with accepted standards of grade, alignment, drainage 

 structures, and foundations, the cost of such elements may be charged 

 for enduring features. Whether roads so built result in the maxi- 

 mum percentage of permanent investment depends in part upon the 

 cost and nature of the wearing surface. For example, a highway 

 completed with all the best enduring features and then surfaced with 

 gravel would show a higher percentage of cost for enduring features 

 than the same road surfaced with more expensive material, as ordi- 

 nary macadam or bituminous macadam. A poorly constructed gravel 

 road, however, where enduring features had been slighted, would 

 present a very high percentage of charge for temporary features. 

 Macadam roads, so called, have been built with bond money by 

 simply spreading broken stone in the mud. An example is shown in 

 Plate I, figure 2. 



1 These examples were selected from States in which records were kept so as to permit cost analysis. 



