58 



TRANSPORTATION ON LAND BY VEHICLES:— THE ROADS 



The Crosset Lumber Company, Arkansas, on their standard gauge spurlines, lay and remove 

 the track in sections with ties attached of one rail length, using the steam log loader for 

 that purpose. 



Grade. A proper survey is very essential. Grades of 11 per cent are feasible on straight track 

 for locomotives having eight drivers. As a rule, however, grades exceeding 5 per cent require 

 the use of geared locomotives. Grades exceeding 8 per cent should be avoided even in that 

 case. A high percentage for a very short distance is, however, permissible. 



Some logging roads in the South have grades running up to 15 per cent for uphill traffic, 

 obtaining the necessary impact by a corresponding downhill grade. The expense of maintenance 

 and of train service added to the frequency of accidents render steep grades highly expensive. 



The standard railroads do not have any grades exceeding 4 per cent. 

 Curves. The minimum radius of curves depends on gauge of track; longest wheelbase; length 

 of timber to be carried, and grade in the curve. Standard railroads do not allow of an angle 

 exceeding 10 degrees. 



In curves, to relieve the increased friction, and, further, to prevent the wheels from jumping 

 the track, owing to centrifugal force, three remedies are required :- 



(aa) Lessened speed and reduced grade. In practice for standard gauge of 56',., inches, for 

 each degree of curvature the grade is released by 0'03 per cent; for narrow gauge by 0"02 

 per cent; 

 (bb) The outer rail is elevated for standard track by '/■.> inch for every degree of curvature; for 



36-inch gauge (usual narrow gauge) by ";; inch for every degree of curvature; 

 (cc) The track is widened in curves by Vn; inch for every 2V2 degrees of curvature. 



(J) BRIDGES. Bridges on forest roads are wooden bridges. 

 There may be distinguished :- 



(a) According to the purpose subserved by the bridge, between "dry spans 

 a dirt fill) and "water spans" (built across a run- 

 ning water course subject to freshets); 



(b) According to the traffic over the bridge, between 

 railroad bridges and waggon road bridges. 



Forest bridges are built of round logs, hewn timber or 

 sawn timber, or of a combination of them. 



Forest bridges are supported by cribs, bents, piers, abut- 

 ments ; by braces underneath or by a hanging system overhead. 



1. Crib bridges. The crib logs should consist of white 

 oak, chestnut, heartpine, &c.; should be saddled one into the 

 other, solidly pinned with dry (locust) pins (l'/> inches) so that 

 the entire crib forms one exceedingly strong basket. The crib 

 should be placed on a solid foundation by removing loose 

 stones, and should, in case of wet spans, foot on a heavy 

 layer of branches, forming a fringe around the base of the 

 crib where running water is apt to undermine it. The crib 

 is filled with stone. Some foresters deem it advisable to 

 floor the crib with heavy half splits so as to prevent the 

 rock from dropping out if the crib is underwashed. On the 

 upper side, the crib exposed to torrential floods is fortified 

 by a nose or keel (frow). This arrangement forces the 

 water and the flood debris through the bridge spans and 

 prevents the underwashing of the cribs. The nose after 



(taking the place of 



A bridge spanning 85 feet across Davidsons's River, 



Biltmore Estate. The two white oak cills supporting- 



the bridge contain each 1,500 feet b. m. 



