The expression
in the formula is known as the engine
factor; it represents the percent of time during a 24hour period
that a road engine is in use. It provides for the pooled use of
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motive power that may make one or more trips per day over a short
division.
The three unknowns in the formula are TD (train density, found
as explained in paragraphs 2.13 and 2.14); RT (running time, found by
dividing the length of the division by the average speed); and TT
(terminal time, found by using table VI). Terminal time is that time
required for servicing and turning locomotives.
Table VI. Terminal Time Average Values
The number of road engines required must be computed for each
division separately. A detailed explanation of how to determine the
road engine requirements is presented in the following paragraph.
3.7. EXAMPLE OF DETERMINING ROAD ENGINE REQUIREMENTS
The division of railroad used in this example is the 110mile
second division given in the example in paragraphs 2.17 and 2.19. It
has a train density of 7, and the track is rated good to fair with a
ruling grade of 1.8 percent. The motive power used for road service
on this division is 0440 dieselelectric locomotives.
Since a value for TD in the formula is known, you must find
values for RT and TT. The length of the division (110 miles) divided
by the average speed gives you the value of RT. Look at table IV.
An average speed of 10 mph is given for a good to fair track with a
ruling grade of 1.5 percent or less. However, the ruling grade for
this division is 1.8 percent; therefore, the more restrictive factor
of 2.5 governs. The average speed, then, is 8 mph. The value for RT
is 14.
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