180 BULLETIN 111, IT. S. DEPARTMENT OF AGRICULTUEE. 



Topography largely fixes the locations, but the general plan of 

 logging determines whether the railroad lines, especially the spurs, 

 shall follow valleys, ridge faces, or the tops of ridges. Spurs are - 

 generally constructed wherever necessary to bring the timber within 

 economic yarding, swinging, or roading distance of the track. 



In most cases the main line enters the tract at the lowest point, 

 following water grade wherever possible, since this location usually 

 gives the best grade out of the region and permits the logs to be 

 hauled down grade. Obviously, this is not possible in all cases, 

 especially where the topography of the country is such that the 

 spur railroads are laid on ridges and the timber yarded up grade. 

 The shortest possible route, naturall}^, is selected, unless heavy cuts, 

 fills, bridge work, and trestle Avork can be avoided by a longer line. 

 Switchbacks are frequently used to overcome sharp changes in the 

 grade. The same end irnij be gained more satisfactorily by doubling 

 back with a curve. This latter method, however, often necessitates 

 a heavier construction expense. Switchbacks often are the only 

 practical means at hand for securing timber from elevations above 

 or below the main line. When the rise in elevation is considerable, 

 it may be advisable to put in an incline. 



Under " Ground yarding," it was pointed out that where the 

 ground is practically level the spur railroads are located so as to 

 gridiron the tract, the distance between the spurs depending for 

 the most part on the cost of the roadbed and the stand of timber 

 per acre. Figures 16 and 17 show how the spur roads may be located 

 in practice. In the first case the conditions from the standpoint of 

 i-ailroad construction approach the ideal. In the second case the 

 ground conditions were harder than usual, which resulted in the 

 timber being yarded and swung relatively long distances to the 

 railroad. Spur railroads are located by the foreman or superin- 

 tendent or b}^ a logging engineer. 



Grades and curvature. — The maximum grades and curvature 

 allowed on any logging railroad vary with the character of the road 

 and the type of locomotives used. Heavier loads must be hauled on 

 the main lines than on the spurs, hence the grades and curvature, 

 must be lighter. If a geared locomotive is used, they may be heavier 

 in either case since a geared locomotive can negotiate heavier grades 

 and sharper curves than a rod engine. 



The direction of the traffic and whether or not there are adverse 

 grades must l)e considered in a discussion of grades and curvature. 

 Traffic on logging railroads moves only one way, the general direc- 

 tion, as a rule, being down grade. Not infrequently, however, ad- 

 verse grades are found on these roads, and they limit the number 

 of cars that can be hauled at a trip. The effect of grade on the num- 



