advanced from FV siding to BO tower under the authority of rule 86. If each
train had lacked time to conform to the respective rule, each would have
remained in its respective FV siding and cleared No. 9 there.
g. Relation to actual practice. This greatly simplified example shows
how a dispatcher keeps two inferior trains out of the way of a superior
train, and how he progresses each as far along the way as possible before
putting it into a siding. In actual practice, however, a division of this
length would be much more congested. When five or six trains are operating
on a single track, the dispatcher is required to do much more planning and
issue many more orders to carry out his objective.
1.8.
DOUBLE-TRACK OPERATION
When operating on double or multiple tracks, a dispatcher is relieved of
considerable strain, and his advance planning is reduced materially.
However, he is still thinking and planning 3 or 4 hours ahead but chiefly
about new trains that may come out on the road. With double track, one is
designated, for example, westbound and the other eastbound; no deviation by
crews is permitted without the dispatcher's specific orders. Since no meets
are scheduled and opposing trains are separated, he proceeds as though
operating separate railroads. His work of keeping inferior trains moving,
yet out of the way of superior ones, still goes on.
If it appears that
double-track operations are quite a bit simpler than single-track operation,
remember that the density of traffic is generally two or three times greater
than on a single line.
Double-track procedures are discussed in the
following subparagraphs.
a. Signals. Most double-track lines are equipped with automatic block
signals by which it is possible for an observer to determine if any trains
occupy the track for the next couple of kilometers ahead.
Many kinds of
signals are used, but only the position-light block signals, currently used
on most American railroads, are discussed.
This signal and the name,
indication, and significance of each aspect is shown in figure 1.3.
An
aspect is the color or position of a signal as it faces an approaching
train.
With the use of such signals, the dispatcher has the problem of
spacing the trains so that the progress of none is hindered by the reduce-
speed and stop signals of the train ahead of it.
Proper train spacing is a delicate phase of dispatching.
If trains
get too close to each other, a great deal of stopping and
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