---+
| NUMBER OF TRUNKS IN GROUP, | MESSAGES PER TRUNK PER |
| MANUAL SYSTEM | BUSY HOUR |
+----------------------------+------------------------+
| 5 | 7 |
| 10 | 9 |
| 20 | 12 |
| 40 | 15 |
| 60 | 18 |
+----------------------------+------------------------+

Some of the reasons for the higher efficiencies of trunks in the
automatic system are not well defined, but unquestionably exist. They
have to do partly with the prompter answering observable in automatic
systems. The operation of calling being simple, a called subscriber
seems to fear that unless he answers promptly the calling party will
disconnect and perhaps may call a competitor. The introduction of
machine-ringing on automatic lines, where existing in competition with
manual ringing on manual lines, seems to encourage subscribers to answer
even more promptly. The length of conversation in automatic systems
seems to be shorter than in manual systems. Still more important,
disconnection in automatic systems is instantaneous during all hours,
whereas in manual systems it is less prompt in the busiest and least
busy hours than in the hours of intermediate congestion. The practical
results of trunk efficiencies in automatic systems are given in Table
XVI.

TABLE XVI

Messages per Trunk in Automatic System

+----------------------------+------------------------+
| NUMBER OF TRUNKS IN GROUP, | MESSAGES PER TRUNK PER |
| AUTOMATIC SYSTEM | BUSY HOUR |
+----------------------------+------------------------+
| 5 | 15 |
| 10 | 22 |
| 20 | 28 |
| 40 | 32 |
| 60 | 34 |
+----------------------------+------------------------+

_Toll Traffic._ Toll or long-distance traffic follows the general laws
of local or exchange traffic. Conversations are of greater average
length in long-distance traffic. The long-distance line is held longer
for an average conversation than is a local-exchange line. The local
trunks which connect long-distance lines wit