| 185 |
| 75 | 170 |
| 90 | 165 |
+----------------------------+---------------------------------------+

_Trunking Factor._ In providing the system of trunks interconnecting the
offices, whether the equipment be manual or automatic, it is essential
to know not only how much traffic originates in each office, but how
much of it will be trunked to each other office and how many trunks will
be required. An interesting phase of telephone traffic studies is that
it is possible to determine in advance the amount of traffic which can
be completed directly in the multiple of that office and how much must
be trunked elsewhere. Theoretical considerations would indicate that if
the local multiple contains one-eighth of the total lines of the city,
one-eighth of the calls originating in that office could be completed
locally and seven-eighths would be trunked out. In almost all cases,
however, it is found that more than the theoretical percentage of
originating calls are for the neighborhood of that office and can be
completed in the multiple. This results in the determination of a factor
by which the theoretical out-trunking can be multiplied to determine the
probable real out-trunking. In most cases, the ratio of actual to
theoretical out-trunking is 75 per cent, or approximately that. In
special cases, it may be far from 75 per cent.

_Trunk Efficiency._ The capacities of trunks vary with their methods of
operation and with the number of trunks in a group. For example, in the
manual system where trunk operators in distant offices are instructed
over call circuits and make disconnections in response to lamp signals,
such an incoming trunk operator can complete from 250 to 500 connections
per busy hour. The actual ability depends upon the number of distant
offices served by that operator and upon the amount of work she has to
perform on each call.

The number of messages which can be handled by one trunk in the busy
hour will depend upon the number of trunks in the group and upon the
system employed. It appears that the ability of trunks in this regard is
higher in the automatic system than in the manual system. For the
latter, Table XV gives representative facts.

TABLE XV

Messages per Trunk in Manual System

+----------------------------+---------------------