38 BULLETIN 257, U. S. DEPARTMENT OF AGRICULTURE. 
The section which was constructed directly under the supervision 
of the Office of Public Roads carries volumimous and heavy suburban 
traffic, both vehicle and motor, and has received no maintenance or 
repairs since its original construction. A new 40-foot steel truss 
bridge was constructed across the slough last October, which resulted 
in unusually heavy additional traffic. For 20 feet on either side of 
the new bridge the macadam has been destroyed. The remainder 
of the experiment now presents an unsatisfactory appearance and is 
very wavy and much worn. There is a series of potholes of various 
sizes and depths, but there is, however, no apparent disintegration. 
The former shoulders have bom used as a roadway until they have 
worn through the subgrade and are largely used by lghter traffic 
to avoid le The crown is well maintained, and the penetra- 
tion has been effective in general, with an excess of oil in places. 
The unevenness of wear, as previously noted, has been due primarily 
to a weak and poorly prepared foundation. Wherever the bond is 
broken the contributory cause appears to be large water-worn gravel 
too near the surface, and lack of uniformity in the distribution of 
the bituminous material, which latter permits early raveling. 
SUPPLEMENTARY REPORT OF EXPERIMENT MADE AT AMES, IOWA, 
1919. 
OiL-ASPHALT GRAVEL. 
The original report of this experiment was published in Circular 
No. 94, and reports of annual inspections were given in Circulars 
Nos. 98 and 99, Office of Public Roads, and in U. S. Department 
of Agriculture Bullet Nos 1050 
When visited on December 19, 1914, there was about 1 inch ‘at 
snow on this road. Scraping hie snow from spots revealed about 
one-half inch of oily dust, covering a well-bonded surface. On 
warming bits of bituminous material in the hands it still developed 
a perceptible stickiness. 
It was learned that an attempt was made in August to remove 
certain irregularities on the surface and to raise the center of the 
crown by means of a light two-wheeled single-blade grader. This 
cut away the high smooth places on the surface, leaving the gravelly 
mixture exposed. However, the traffic compacted this surface and 
it bonded again in very good shape. There was and is now some 
roughness perceptible to automobile travel caused by the uneven dis- 
tribution of the material which was brought to the center for the 
purpose of raising the crown. 
Traffic on this mad is considerable, although it consists mainly of 
automobiles, carriages, and light wagons, since most of the heavy 
trucking enters the college grounds by another road. 
