152 
BULLETIN 711, U. S. DEPARTMENT OF AGRICULTURE. 
Fore-and-aft roads may be constructed on almost any grades. The 
usual grade of a downhill road ranges from 5 to 25 per cent. Grades 
of 30 per cent or more, if of considerable length, are likely to lead 
to trouble through the logs running and jumping out of the road. 
Adverse grades may and do occur in these roads, although it is 
preferable to keep the adverse grades down to 10 or 15 per cent. 
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Fig. 59. — Method of using compressed air snubbing machine. 
Roads having adverse grades of 40 or 50 per cent have been used. 
An engine is generally required at the top of any long or very steep 
adverse grade. 
The best results are obtained from straight roads, because curves 
increase the friction, reduce the hauling ability of the engine, cause 
greater wear on the cable, make it difficult to keep the logs in the 
road, increase the maintenance cost of the road, and curtail the 
output. Curves, however, are necessary in many cases to change the 
general direction of the road. Short curves or reverse curves are 
out of the question, and usually not more than two or three curves 
are practicable, even in the longest roads. A change of 90 degrees 
in the direction of a road may be made by means of two long and 
gradual curves. 
In constructing the roads the ends of the logs are joined together, 
the tops being placed in the direction in which the logs are hauled. 
In the case of a two-pole road the logs are placed from 6 to 8 inches 
