2 BULLETIN 586, U. S. DEPARTMENT OF AGRICULTURE. 
types of roads. Other purposes have been to investigate the value, 
as a road-surfacing material, of earth-oil asphalt, made by admixing 
asphalt with a prepared mixture of earth and water; and to secure 
check results with certain types of bituminous macadam that have 
been employed in previous experiments of the office. The culvert 
investigation is for the purpose of determining the relative merits 
of various kinds of steel and iron used in the manufacture of corru- 
gated pipe. 
Supplementary reports, describing the progress of experiments 
previously reported, follow the reports of the new experiments. 
To these supplementary reports are added, in several cases, summaries 
showing an outline history of the projects to date. Also, the histories 
of several projects that have been discontinued are summarized in 
this bulletin so as to make the experimental results already obtained 
by the office easier for the interested reader to follow. 
Note.— In this publication "bituminous macadam by the penetration method" is called simply bitu- 
minous macadam, and "bituminous macadam by the mixing method," bituminous concrete. 
NEW EXPERIMENTS. 
The new experiments included bituminous macadam and bitu- 
minous gravel construction on the Russell Road in Alexandria 
County, Va. ; bituminous gravel concrete and earth-oil asphalt on 
the Alexandria- Accotink Road in Fairfax County, Va. ; and the bitu- 
minous surface treatment -of a new gravel road leading from Gum 
Spring to Mount Vernon in Fairfax County, Va. In addition the 
special experiments with corrugated metal culverts were initiated on 
the Texas post road. 
EXPERIMENTS ON RUSSELL ROAD, ALEXANDRIA COUNTY, VA. 
BITUMINOUS MACADAM AND BITUMINOUS GRAVEL. 
This experimental project is located in Alexandria County, Va. 
The road begins at station + 00 or station 114 + 47.3 of the Mount 
Vernon Avenue experimental road, and runs in a general south- 
westerly direction on a new location to station 21+40. From there 
it continues in the same general direction over an old worn-out 
gravel road to the city line of Alexandria. The project is 8,761.4 
feet in length and is divided into eight experiments, as shown in 
Table 1. The experiments are numbered consecutively from station 
+ 00 toward Alexandria. The experimental surfaces were con- 
structed on a 6-inch pit-run gravel base throughout. Work was 
begun by contract July 12, 1915, and completed June 20, 1916. The 
total cost of the project was $22,844.94. 
