A joint consideration of
the speeds, braking efforts, and profile of the road were then used to
determine at each and every point on the line the minimum allowable
distance between trains, so that the train in the rear could be
stopped by the automatic application of the brakes before reaching a
train which might be standing at a signal in advance; in other words,
the length of the overlap section was determined by the local
conditions at each point.
In order to provide for adverse conditions the actual braking
distances was increased by 50 per cent.; for example, the braking
distance of a train moving 35 miles an hour is 465 feet, this would be
increased 50 per cent. and the overlap made not less than 697 feet.
With this length of overlap the home signals could be located 697 feet
apart, and the block section length would be double this or 1394 feet.
The average length of overlaps, as laid out, is about 800 feet, and
the length of block sections double this, or 1,600 feet.
[Illustration: VIEW UNDER CAR, SHOWING TRIGGER ON TRUCK IN POSITION TO
ENGAGE WITH TRACK STOP]
The protection provided by this unique arrangement of signals is
illustrated on page 143. Three positions of train are shown:
"A." MINIMUM distance between trains: The first train has
just passed the home signal, the second train is stopped by
the home signal in the rear; if this train had failed to stop
at this point, the automatic stop would have applied the air
brake and the train would have had the overlap distance in
which to stop before it could reach the rear of the train in
advance; therefore, under the worst conditions, no train can
get closer to the train in advance than the length of the
overlap, and this is always a safe stopping distance.
Pages:
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176