30 BULLETIN 407^ U. S. DEPARTMENT OF AGEICULTUBE. 



Experiment No. 4- — The appearance of this section is similar to 

 that of experiment No. 3, but the mat is thinner and the hmestone 

 aggregate of the macadam is shghtly but quite uniformly visible 

 over the entu-e section along the central portion of the road. Some 

 excess top-dressing still remains along the shoulders. It is probable 

 that the section will require re-treatment in the spring. 



Experiment No. 5. — The mat on this section is softer than that on 

 sections 3 and 4, but much less leathery than that on section 2. 

 The macadam shows through in a few places, but the mat is not 

 broken at any point. It is probable that this section wiU require a 

 re-treatment late in the summer or fall. About 300 feet from the 

 south end of the section there is an area about 20 feet in length and 

 extending nearly the entire width of the road, where the sm^ace was 

 rather badly burned as the result of the burning of a blacksmith shop 

 and stables near the road. 



EXPERIMENTS ON BRADLEY LANE, MONTGOMERY COUNTY, MD. 



BITUMINOUS MACADAM (PENETRATION METHOD). 



The experiments previously reported for this road have been dis- 

 continued because the design was considered inadequate for the 

 prevailing tra^ffic. The traveled way was only 10 to 12 feet wide, 

 while the road carried practically as heavy traffic as the adjacent 

 section of the Rockville Pike. Partly also because of the exceedingly 

 poor drainage and foundation conditions, it had never been possible 

 to maintain the surface satisfactorily, and it had become rutted and 

 was continually breaking into potholes, while the edges were badly 

 cut and sheared by traffic. Finally, in June, 1915, arrangements wore 

 made to reconstruct the roadway as a new experiment, and a bi- 

 tuminous macadam surface, constructed according to the penetration 

 method, was the type of improvement adopted. 



The old surface-treated macadam was scarified, reshaped, and 

 widened by the addition of new material to form the foundation 

 course for the new surface. The total length of the road is 3,813.5 

 feet. The width of the new roadway was made 16^ feet from 

 Connecticut Avenue westward for approximately 2,404 feet by adding 

 2^ feet to the south side and 4 feet to the north side of the old surface; 

 the remaining distance to Wisconsin Avenue was made 15 feet wide 

 by adding 2J feet to each side of the old sm^face. In preparing 

 the foundation course it was necessary to add 145 tons of new Eme- 

 stone; and in order to increase the stabHity of the foundation, 3,646 

 linear feet of 4-inch drain tile was used. The drain tile was placed 

 under the south gutter of the road at a depth of a foot or more below 

 the surface, and is expected to correct the unsatisfactory foundation 

 condition referred to in the preceding paragraph. The drainage 

 was further improved by cleaning, out aU existing culverts and 



