DUST PREVENTION AND ROAD PRESERVATION, 1916. 35 
tegrate so noticeably as the other three granite sections. It was 
placed in good condition with penetration patches and received a 
surface treatment in May. The same bituminous material was used 
as for the treatment on experiments Nos. 17, 18, and 19, and cost 
data and quantities are given in Table 38. At the time of inspection 
this experiment was in almost perfect condition. 
Corrugated metal culverts.—The corrugated metal culverts on the 
Mount Vernon Avenue experimental road were inspected at the same 
time as the road surface, and were found to be in good, sound con- 
dition. There was no appreciable difference in the amount of rust- 
ing, although all were covered with a thin layer of rust. In the case 
of the coppered-iron and ingot-iron culverts this rust seemed to be | 
somewhat more easily rubbed off than in the case of the others, 
leaving smooth black metal exposed. The rust in the open-hearth 
steel culverts appeared to be of a more scaly nature than in the 
others. 
Table 40 shows a traffic census record for the entire project, and 
Table 39 the maintenance cost record for the calendar year. The 
cost figures in Table 39 include the cost of surface retreatments 
given in Table 38. 
