TRENDS IN PRACTISE AS AFFECTING COORD I NATION 175 



In the distribution field also, coincident with the development of 

 rural service, there has been a movement to higher voltages in primary 

 circuits, and indications point to the continuance of this trend in the 

 future. Due to the distances involved, voltages from 6600 to 13,200 

 (and even higher) have been used in rural work. In urban areas the 

 high load densities encountered in some districts require the handling 

 of large blocks of power in the primary circuits, and the lower primary 

 voltages have often been replaced by higher voltages for such conditions. 

 In addition to the greater capacities provided by the higher voltages, 

 possibilities of system simplification by combining rural and urban 

 systems and eliminating voltage transformations are of considerable 

 economic importance. 



While at first glance the pronounced trend to higher transmission 

 and primary distribution voltages may appear to enhance the difficult- 

 ies of coordinating communication and power lines, certain factors 

 enter to offset this. As transmission voltages increase, line construc- 

 tion as a whole becomes more massive, greater clearances and wider 

 rights of way become necessary and construction costs per mile 

 rapidly rise. These greater space requirements weigh against the use of 

 highway locations and, together with the higher construction costs, 

 which make the shortest possible lengths desirable from an economic 

 viewpoint, frequently influence the selection of direct cross-country 

 private rights of way providing generally greater separation from 

 communication circuits in the same territory. 



TABLE III 

 Total Circuit Miles of Transmission Lines. 

 Years 1926-1929 Inclusive 



By Voltages, 



* This apparent discrepancy is believed to be due to reclassification of these lines 

 as between transmission and distribution facilities. 



