430 



BELL SYSTEM TECHNICAL JOURNAL 



Associated Avith this development of the telephone plant has been 

 a very rapid increase in trat^c. Fig. 1 indicates this increase in 

 the United States and Canada since 1915. A striking characteristic 

 of this growth is that the increase has been much more rapid for the 

 longest lengths of haul than for the shorter lengths of haul. For 

 example, during the last five years in which the messages on lengths 

 of haul up to 250 miles approximately doubled, the messages on 

 hauls from 250 to 1,000 miles increased five times and those over 

 1,000 miles increased more than ten times. This characteristic is also 



1000 



800 



600 



400 



200 



1915 



1920 



1925 



1930 

 ( EST.) 



Fig. 1 — Total toll messages in millions per year — Bell system. 



illustrated in Figs. 2, 3, and 4 which show respectively the growth 

 in the number of circuits between Toronto and Detroit 240 miles in 

 length, Buffalo and Chicago 550 miles in length, and direct circuits 

 from New York and Chicago to the Pacific Coast, averaging about 

 2,500 miles in length. This particularly rapid growth in very long 

 haul trafftc has made it practicable to establish a considerable number 

 of long haul circuit groups and has greatly assisted in the problem of 

 handling satisfactorily calls between widely separated points. It has 

 led to the condition today in which 74 per cent of the long distance 

 (Long Lines) messages are handled over direct circuits and 20 per cent 

 with one intermediate switch. 



