152 



BULLETIN 711, V. S. DEPARTMENT OP 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. 



Eoads 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 usualh^ 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 



