498 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



(h) The nature of the present traffic, with special reference to the 

 amount of heavy trucking. 



(c) The probable future traffic which will use the road after 

 improvement. 



A consideration of the last item above naturally leads to the second 



froup of data which is considered in approving a project. This group 

 as to do with — ■ 



(a) The type of adjacent roads. 



(b) The relation of the proposed road to the State road system. 

 Successful and adequate improvement of adjacent or contiguous 



roads frequently assists in determining what type will be adequate 

 under traffic likely to develop ; and the part which the new^ road will 

 play in the general vState system is further indication of the probable 

 future traffic. 



Because of abnormal conditions in the materials market during the 

 past year and the difficulty of securing transportation facilities, many 

 projects have been affected; but entirely aside from these abnormal 

 conditions, which temporarily affect materials and methods of con- 

 struction, a third group of considerations is applied in determining 

 the adequacy of Federal-aid projects. The elements of this group 

 are — 



(a) The quality and kind of local materials available for construc- 

 tion. 

 • (6) Peculiar local conditions affecting construction. 



(c) Prevailing practice in highway construction in the State or 

 locality. 



It is frequently found that suitable local materials are so much 

 less costly than better materials imported from a distance that the 

 construction of a lower type of work with the local material is justi- 

 fiable, and as it is important to develop material sources throughout 

 the country on as large a scale as possible, approval of the use of 

 local materials is not infrequently made for the purpose of encour- 

 aging local production. There are also occasional peculiar condi- 

 tions affecting the methods of construction. For instance, in parts 

 of the far West the entire absence of water along a right of w^ay and 

 the expense of piping an adequate supply for 20 or 30 miles makes 

 the construction of any type requiring large C|uantities of water 

 uneconomical, and under these conditions other types are approved 

 which can be constructed without the use of large quantities of 

 water. The local practice must occasionally be considered, because 

 of the difficulty of securing contractors when unusual or strange 

 requirements regarding the work are insisted upon. For this reason 

 the prevailing practices of the State in certain details of construction 

 are admitted as affecting the design and type of work. 



The last group of considerations is of a more technical nature and 

 is at the present time confined to the results of experiments and 

 studies made by the bureau and believed to be applicable to a greater 

 or less extent in determining the substantial nature of proposed pave- 

 ments. These experiments have to do with the resistance of the 

 commoner types of pavement construction to impact and to the 

 effects of heavy motor truck traffic. Studies of soil conditions in 

 progress under the direction of the bureau likewise furnish additional 

 information which can be applied in determining whether the designs 

 for bases and sub-bases of pavements are adequate. 



