Measuring the Wear of Roads 



A means by which the right material 

 for the right place is determined 



THERE are now approximately two 

 million, three hundred thousand miles 

 of public roads in the United States, 

 not including the streets of our incor- 

 porated towns and cities. The materials 

 which are used in them differ, varying 

 from concrete and macadam to cob- 

 ble stones 

 and dirt. The 

 determining 

 of the right 

 material for 

 the right 

 place is a 

 problem the 

 solution of 

 which would 

 save many 

 millions of 

 dollars. 



The impor- 

 tance of this 

 consideratio n 

 has led the 

 Office of Pub- 

 lic Roads and 

 Rural Engi- 

 neering to attempt 



Steel block -"'>«--- 

 Electric cable— *C__^' 



The equipment with which the wear on roads is measured. The 

 concrete blocks hold the fine wire which is stretched across the road 



to secure definite in- 

 formation on the wearing qualities of dif- 

 ferent materials under different conditions 

 of traffic. For this purpose, the office has 

 adopted a method which is very accurate. 

 A brass plug is permanently buried in 

 each side of the road, three-quarters of 

 an inch below the surface. Between these 

 plugs a wire is stretched by means of the 



concrete blocks shown in the photographs. 

 One of these blocks is pivoted on the ver- 

 tical rod which passes through it in front, 

 the weight of the block being utilized to 

 keep the wire taut. By placing the vertical 

 rod of each block so as to stand on its 

 respective brass plug, and by then 

 adjusting the 

 length of the 

 wire until the 

 bubble- level 

 shows the 

 rod to be 

 "plumb," the 

 fine wire will 

 always 

 stretch across 

 the road in a 

 certain line 

 which will 

 notvary,how- 

 ever much 

 the road 

 may be worn 

 down. 



Having es- 

 tablished a 

 measuring line, the rest is easy. A steel 

 block is placed upon certain spots across 

 the road and a caliper measures the vertical 

 distance from it to the wire. This can be 

 obtained very accurately because the cal- 

 iper screws upward and when the top of it 

 just touches the wire, an electric circuit is 

 closed and a buzzer rings. Repeating this 

 measurement reveals the amount of wear. 



A fine wire is stretched across the road. By noting the differences in distance between 

 it and the road at intervals of time the rate of wear of the road is readily determined 



413 



