474 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 



serve to confirm this observation, the indications being that beams 

 subjected to repeated applications of load will fail under loads con- 

 siderably less than would be required to produce failure with a single 

 application. 

 With the Univeesity of Georgia and Georgia State Highway Department, 



An investigation of the effective life of sand-clay, topsoil, and 

 similar roads in the State system of Georgia is in progress. In view 

 of the extensive use of these types of road surface in those States 

 whose road systems are in the stage of development, it is very de- 

 sirable that definite information in regard to their life be available 

 in order that their comparative economy with respect to other types 

 of higher initial cost and longer life may be determined. 



With the Engineering Experiment Station, Iowa State College. 



An important investigation of the resistance of various kinds of 

 road surface to traction of motor vehicles, which is being conducted 

 by this experiment station with our cooperation, has already pro- 

 duced information of the greatest value. It is indicated that the sav- 

 ing in gasoline consumption resulting from the paving of an earth 

 road is sufficient on the heavily traveled trunk highways to pay the 

 entire cost of surfacing in a remarkably short time. 



With the same experiment station investigations are also under 

 way to determine the effect of impact on highway bridges and also 

 to determine the load transmitted to highway culverts through 

 various depths of fill and the effect of impact delivered through such 

 fills. In the investigation of the effect of impact on bridges a new 

 photographic strain gauge, designed by the bureau, is being used to 

 measure the instantaneous deformations which are caused by the 

 impact of vehicles. The instrument is so designed that inertia of 

 moving parts is reduced to a minimum. It responds quickly and 

 indicates the stress under very high impact conditions. 



With the Massachusetts Institute of Technology. 



An important research on the tractive resistance of roads has been 

 conducted in cooperation with this institution and the Quartermas- 

 ters Department, United States Army. It is closely related to the 

 tractive-resistance investigations at Iowa State College. 



Other cooperative investigations which have been under way dur- 

 ing the fiscal year are listed as follows : 



With the engineering experiment station, University of Texas : 



1. Study of wear-resisting properties of concrete aggregate. 



2. Effect of moisture on volume change in soils. 

 With New Hampshire State Highway Department: 



Study of sands of New Hampshire for use in concrete. 

 With the' University of Maryland and Maryland State Roads Commission: 



Effect of traffic and climatic changes on the character of concrete. 

 With the engineering experiment station, Kansas State Agricultural College : 



Investigation of wind resistance to motor vehicles. 

 With the North Carolina State Highway Commission : 



Sand-clay and topsoil road investigations. 

 With the American Association of State Highway Officials, committee on tests, 

 and the New York State Highway Commission: 



Causes of disintegration of concrete roads in New York State. 

 With the National Academy of Sciences, advisory board on highway research 

 of the National Research Council: 



1. Census of highway-research projects in the United States. 



2. Formulation of a national program of highway research. 



