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taken to avoid premature reservation of this block for another train when a train leaves
the block. There is also a disadvantage for passing trains. Let us assume that a train is
passing the block from the left to the right and that a route is to be activated before the
block ahead, to the right of this block. As soon as the passing train enters the block at A
the route is activated. In the same moment the train begins to slow down, because A is
also a brake indicator and the train has to wait, until the route is reported to be activated
which needs a certain time. This can be avoided by adding an additional contact according
to the following diagram:
A B C
Diagram 93: Block with three momentary sensors
In Diagram 93 the indicator A is used as stop indicator for trains running to the left, C
acts as stop indicator for trains running to the right. Indicator B acts as a brake indicator
for trains running in both directions. In this configuration block occupancy is not indicated,
too, and as in Diagram 92 certain measures are to be taken to avoid premature
reservation of this block for another train when a train leaves this block. But trains can
pass this block without any speed changes, even if there is a route to be activated before
the block ahead – provided the distance between A and B or C and B, respectively, is
large enough that the route can be activated after passing A or C, respectively, and before
reaching B.
All examples discussed so far can be applied for blocks passed by trains in both directions.
The configuration can be made simpler if trains pass a block only in one direction.
This is shown in the following:
B C
Diagram 94: Block with two occupancy sensors
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