DUST PREVENTION AND ROAD PRESERVATION. 35 



developing irregular humps throughout the entire length of the 

 section, which in places were easily 3 inches above the actual cross 

 section of the road. To remedy this condition the humps were 

 either trimmed off or entirely removed with a shovel until the clean 

 macadam stone was exposed. The material thus removed was gener- 

 ally quite rich in bitumen and was distributed where required in order 

 to improve the cross section of the surface. These fresh patches 

 were protected by a thin covering of screenings, and they held in 

 place well, so that at the time of inspection the section presented a 

 much improved and fairly uniform appearance. 



The cost of maintenance on this section for the year amounted to 

 $19.05, or 1.88 cents per square yard for the entire section. 



Section No. 11. — Native asphalt emulsion — Macadam resurfacing. 



No further treatment has been given to this section, and it pre- 

 sents a smooth, firm, and satisfactory appearance. Owing to the 

 omission of any finishing coat of bituminous material, there were 

 two small areas on the east side near the north end in which the 

 coarse stone could be seen. These did not ravel or wear appreciably, 

 but in conjunction with other repairs they were recently painted 

 with a thin coat of cold refined water-gas tar preparation and cov- 

 ered with a light scattering of screenings. 



SUPPLEMENTARY REPORT OF EXPERIMENTS MADE ON BRADLEY LANE, 

 CHEVY CHASE, MD., 1911. 



REFINED SEMIASPHALTIC OIL. 



The original report of these experiments was published in Circular 

 No. 98, and the report of an inspection at the end of a year's service 

 may be found in Circular No. 99. The following report covers the 

 condition of the experiment at the end of 1913, and the repairs up to 

 date. 



The surface treatment of Bradley Lane was originally treated as 

 three distinct experiments, but owing to the fact that the conditions 

 on all three sections have become, in general, the same, they will be 

 considered as a unit. The formation of a thick mat or hump on the 

 outer edges of the roadway where the heavier treatment had been 

 applied was noted in Circular No. 99. The wear throughout the 

 entire traveled way became more pronounced during the past year; 

 the surface was exposed in long shallow depressions of varying length; 

 and a number of depressions ranging in depth from 1 to 2 inches 

 developed. It was found that the mat along the sides was rich in 

 bitumen which still possessed good adhesive qualities, and the mixture 

 was therefore used for filling the worst depressions. When tamped 

 into place and covered with a thin layer of screenings, a satisfactory 

 and firm patch soon resulted through compression by traffic. By 



