510 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 9 



dissipated in clouds of dust. Also the impact of the heavy concen- 

 trated wheel loads of the motortrucks exceeded the powers of resist- 

 ance of the old-style wagon road. Modifications were needed in both 

 the old road surface and the new motor vehicle. To discover a 

 rational solution to these problems the first large-scale highway re- 

 search was begun, in 1920, in Federal laboratories at Arlington, Va., 

 and on experimental roads at Bates, 111., and Pittsburg, Calif, (pi. 14, 

 fig. 2) . These tests were instrumental in bringing about the adoption 

 of pneumatic balloon tires and the thickened-edge design of 

 pavements. 



Faced now with the popular desire for travel on rubber, road- 

 building agencies were converting as rapidly as possible the early 

 disconnected roads of each State into continuous long-distance routes. 

 In the neighborhood of towns motorists were able to find their way 

 in spite of the crude direction signs. When a long journey was ven- 

 tured, however, the highway traveler was confused by the motley 

 array of informational signs erected independently in each State. To 

 bring order out of chaos and thus speed the tourist on his way uni- 

 form numbered United States shields, and warning, danger, and in- 

 formational signs were adopted, in 1925, for Nation-wide use by the 

 Joint Board on Interstate Highways appointed by the Secretary of 

 Agriculture. Soon maintenance crews were at work dismantling the 

 old markers and erecting new ones (pi. 15, fig. 1). 



The volume of road construction spurred on by the growing num- 

 ber of motor-vehicle registrations had grown steadily over a long 

 period of years when a sharp increase in Federal road-building 

 activities was authorized as an antidote to the protracted business 

 depression following the financial crash of 1929. All road improve- 

 ment was quickened, in 1933, by large appropriations made by Con- 

 gress to provide work for the unemployed. Speeding work on the 

 main highways and city streets, the Federal Government also for 

 the first time extended Federal aid to the improvement of the farm- 

 to-market roads (pi. 15, fig. 2). 



To provide further gainful employment special Federal funds were 

 appropriated to make railroad grade crossings safer (pi. 16, fig. 1). 

 The need for this work was emphasized by the mounting heavy toll 

 of traffic accidents. The thousands of bridges that have been built 

 each year, since 1934, with these funds will safeguard many lives 

 and limbs and also save motorists annoying stops while waiting 

 for passing trains. 



In cities, too, the new Federal funds for the elimination of hazards 

 at railroad grade crossings made possible the construction of long 

 viaducts. These structures, as early as 1935, began to do away with 

 many dangerous crossings. Furthermore, these viaducts put a stop 



