THEORIES FOR TOLL TRAFFIC ENGINEERING IN THE U. S. A. 425 



4 5 6 7 8 9 10 

 NUMBER OF TRUNKS 



30 40 50 



Fig. 2 — Permitted intertoU trunk occupancy for a 6.5-minute usage time 

 per message. 



the expected, or average, delay in seconds for calls to obtain an idle 

 trunk in that group during the average Busy Season Busy Hour. In 1954 

 the system "average trunk speed" was approximately 30 seconds, re- 

 sulting from operating the majority of the groups at a busy-hour trunk- 

 ling efficiency of 75 to 85 per cent in the busy season. 



The T-engineering tables show permissible call minutes of use for a 



