SELECTING THE TYPE OF CONSTRUCTION 29 



circuits up to 25 to 30 miles in length. This has only one-half the weight of No. 9, 

 and both the first cost and cost of transportation are, therefore, reduced one-half. 

 There are nearly twice as many tfes on a tree line as on a pole line. The cost for 

 insulators is, therefore, considerably increased. As split tree insulators generally cost 

 more per thousand than pony glass insulators and brackets together, this cost is more 

 than doubled on a tree line. 



Stringing wire costs materially more on tree lines than on pole lines. This is 

 true even with experienced labour. The most obvious cause of greater cost is the 

 much greater number of ties to be made, as previously mentioned. Further, it is 

 harder to reel out wire for a tree line, and care must be used to get the wire on the 

 right side of each tree; which is less necessary with poles. Trees are also harder to 

 climb than poles, especially where they are large or have a loose, scaly bark, and it is 

 necessary for the linemen to spend much time trimming the trees as they ascend them. 

 Finally, the wire cannot be stretched to give the proper sag allowance in half-mile 

 spans as it can with poles, but the sag must be distributed from tree to tree by the 

 linemen often with the constant assistance of a groundman. 



The most difficult element in tree-line construction, however, is the problem of 

 securing efficient labour and supervision. In pole-line work, methods are largely 

 standardized and relatively simple for lines of only one or two wires, such as those 

 used for forest telephone circuits. About the only problem requiring the exercise of 

 judgment is the bracing and guying of poles on curves and at abrupt turns. In tree-line 

 work, on the other band, nearly every support presents a new problem. Experienced 

 builders of tree lines are practically non-existent in Canada, and attempts to use line- 

 men experienced in ordinary pole-line methods have usually been attended with very 

 unsatisfactory results. Unless, therefore, a large enough mileage of tree line is to 

 be built to justify the training of special line builders, or unless an experienced fore- 

 man is available, it will be found more satisfactory to employ the standard pole-line 

 methods even in timbered regions. This will be quite generally true where the timber 

 stand is relatively light, making the clearing of a right of way easy, and where suit- 

 able poles of durable species are readlily secured along the line. 



Where a large mileage of line is to be built in big timber, or where the line passes 

 in large part through large fire-killed, dead, or overmature timber where windfalls are 

 frequent and the cost of right-of-way clearing would be prohibitive, tree-line methods 

 are often the only practicable construction that can be employed. These methods are 

 described in detail in this manual, and if the purpose of the peculiar type of con- 

 struction employed is understood and the methods prescribed are followed 1 faithfully 

 and intelligently entirely satisfactory lines may be built through the most unfavourable 

 timber at very reasonable cost. 



Section 36 Sketch of the Development of Tree-line Methods 



Although thousands of miles of so-called tree lines have been built by railway 

 construction companies and others for temporary use, the credit for devising a method 

 by which tree lines may be built to be of permanent utility belongs to the United 

 States Forest Service. This service has approximately 25,000 miles of lines in use on 

 the National Forests of the United States, a large part being tree lines, and is con- 

 stantly extending these lines as funds become available. The experience on which its 

 methods are based has been secured under the personal direction of expert telephone 

 engineers on thousands of miles of line constructed over a period of fifteen years. 

 Beginning with the makeshift methods of construction commonly employed for 

 temporary low-priced lines by railway contractors, there has rapidly been developed 

 under actual working conditions a low-priced method for building permanent lines 

 specially adapted to forest conditions, and a large amount of equipment has been 

 designed to meet the special conditions encountered on these lines. The first tree 

 lines built followed rather closely pole-line methods. These rapidly became useless. 



