204 POWER DISTRIBUTION FOR ELECTRIC RAILROADS.
frequent. 'These sizes give more room for the larger
motors required and are better adapted for the cars.
As to track, careful laying and good ballasting are
the essential points. The rails themselves are what would
be used for a light steam railroad, forty to sixty pound T
being the rule, although at the termini the usual girder
rails often have to be employed. It should be remembered
that a city track gets far more wear and tear than the
average interurban track and must be, accordingly, even
more substantial.
The rather infrequent stops in interurban work pro-
duce on the whole a tendency toward uniform distribution
of load that operates favorably on the necessary distribu-
tion of power. The service is less liable to blockades, it
is easier to hold to a regular schedule and there is less of
the troublesome shifting of the load, than in street railway
practice. Consequently it is somewhat easier to plan the
feeder system. :
On the other hand, the average distance to which
power has to be transmitted is considerable, so that the
aggregate amount of feeder copper is great, and it is ag-
gravated by the frequent attempts to transmit power un-
reasonably long distances at 500 volts to avoid distributed
stations or other appropriate methods.
The absolute amount of power required per car is, for
an approximation, nearly double that required for a stand-
ard double truck car in street railway work. The speed
of the interurban car is nearly double, and the car itself is
often heavier. On the other hand the average live load is
likely to be smaller and the power wasted in stopping and
starting is less. On the ordinary urban railway twenty
to twenty-five amperes per car is not far from the aver-
age power required through the day; on a busy interurban
line forty to forty-five are likely to be required, or thirty
to forty if the traffic be moderate.
Consequently heavier motors are often employed than
on street railways, although for many cases they are un-
necessary. If the trafficis likely to be large or if the speed
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