TELEPHONE SYSTEM OF THE UNITED STATES 



45 



Telephone Toll Lines 



To handle the toll business of the United States has required com- 

 pleting a network of toll telephone lines completely covering the 

 country. This network is shown in a general way in Fig. 35. It 



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1928 1929 1930 1931 1932 1933 



Fig. 36 — Estimated toll circuit kilometers in plant Bell Operating Companies. 



consists at the present time of about 14 million kilometers of wire on 

 about 300,000 kilometers of toll route. The toll circuits are partly 

 open wire, supported on insulators and are partly in cable. Both the 

 open wire and cable circuits are, in general, phantomed, giving three 

 independent circuits for each two pairs of wires, and in addition on 

 the open wire is superposed a considerable amount of carrier current 

 telephone circuits. The distribution at the present time between 



