may be installed which mechanically grip the wheel flanges of moving
cars and create friction to reduce speed.
When car retarders are
used, switchtenders usually are not employed.
The retarder
operators, generally stationed in towers, open and close the switches
by electrical control. Hump switching is faster than the older back-
and-forth (flat-yard) switching because the movement is continuous
and in a forward direction only.
c. Departure yard.
When tracks are filled in yard B of fig.
1.1, cars are moved to the departure yard, C.
When enough cars
accumulate on a track in yard C, an outbound road crew is ordered to
move the train to the next division terminal.
Or when sufficient
cars of the proper classification accumulate on various tracks, they
are doubled together as described in chapter 2, paragraph 2.8.
d. Advantages.
The principal advantage of the progressive yard
is the reduction in delays to both yard and road crews. When a road
train stops in yard A, the engine may proceed immediately to the
running track and then to the roundhouse.
If switching were in
progress on this lead, the yard engine would have to stop operations,
pull up to clear the running-track switch, and thereby lose valuable
time. The same situation would prevail if road trains were departing
from the classification yard. Here, delay to a switching crew would
be considerably greater. A slow-starting train might block the lead
for as long as 15 minutes.
Should the train be delayed in getting
dispatcher permission to head out on the main track, the loss of time
could be much greater.
1.4. COMBINATION YARD
Railroads frequently incorporate the receiving, classifying, and
departure facilities into one yard.
This may result from
insufficient volume of work to justify three separate yards or from a
lack of land to expand the yard layout.
In combination yards, the
number of tracks depends on the volume of traffic, and track length
is determined by the established length of inbound and outbound
trains. These yards are generally flat, and switching is done by the
back-and-forth movement of a yard engine with cuts of cars.
In a
combination yard, it is impossible to arbitrarily assign specific
tracks for receiving only. Road trains must be taken into the yard
without delay to prevent blocking the main track.
Just which track
is used is a decision for the yardmaster. In a crowded yard, he may
be forced to accept a train on any track able to accommodate
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