DUST PREVENTION AND ROAD PRESERVATION, 1915. 67 
SUPPLEMENTARY REPORT OF EXPERIMENT MADE AT AMES, IOWA, 
1910. 
OIL-ASPHALT GRAVEL. 
The original report of this experiment was published in Circular 
No. 90, and reports of succeeding annual inspections appear, respect- 
ively, in Circulars Nos. 98 and 99 of the Office of Public Roads and in 
U. S. Department of Agriculture Bulletins Nos. 105 and 257. 
The driveway on which this experiment was made is 27 feet wide 
between gutters, but owing to local conditions traffic is confined 
practically to the eastern two-thirds of the pavement. Several 
slight inequalities appeared in the traveled way in 1914, and these 
were partly eliminated by reshaping the road with a grader. The 
surface was then treated with a light asphaltic oil, but the effect of 
this treatment had almost entirely disappeared in December, 1914. 
In June, 1915, a similar treatment of very light oil was applied, with 
no more permanent effect than that of the previous one. 
In October, 1915, a heavier asphaltic oil was applied to the traveled 
portion of the road at the rate of one-half gallon per square yard. 
This work was done under the direction of the superintendent of the 
grounds and represents the manitenance the roadway has received 
since its construction in 1910. When inspected December 10, 1915, 
the gravel surface was well crowned and was covered with a cushion 
about three-fourths of an inch thick, slightly wavy, but dense and 
well compacted. 
SUPPLEMENTARY REPORT OF EXPERIMENTS MADE AT KNOXVILLE, 
TENN. 
TAR AND OIL PREPARATIONS. 
The original report of these experiments was published in Circular 
No. 94, and reports of subsequent annual inspections appear in 
Circulars Nos. 98 and 99, Office of Public Eoads, and in U. S. Depart- 
ment of Agriculture Bulletins Nos. 105 and 257. The last inspection 
was made December 10, 1915. 
These experiments consisted of three bituminous macadam sections 
constructed by the penetration method. The binders used were, for 
section No. 1 a refined coal tar, section No. 2 a refined tar preparation, 
and section No. 3 an oil-asphalt. By January, 1913, section No. 1 
had raveled throughout its entire area and by November, 1914, had 
failed completely except for two small areas. Section No. 2 showed 
only a small number of raveled places in January, 1913, but by 
November, 1914, had become so seriously pitted that reconstruction 
seemed necessary. Both sections impeded motor traffic noticeably. 
Section No. 3, on the other hand, was still in excellent condition. 
In the spring of 1915 the county road officials ordered the holes in 
sections Nos. 1 and 2 filled with crushed stone. After this rock had 
