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Modeling railroad block signals

You can use Vissim to model the operation of railroad block signals and railway traffic, including train protection systems according to the German regulations for tram construction and operation (BOStrab).

Trains are not driven "on sight". The drivers rely on signals and may only drive within blocks released for passage. A block is defined as the area between two block signals. Only after a block has been left by one train is the next train allowed to enter it. Entry to the blocks is controlled via block signaling.

In Vissim you model blocks via signal heads. Signal heads defined as block signals do not belong to a signal group or signal control.

1.  Place the signal heads on the link at the desired block distance (Defining signal heads).

2.  For the signal heads, select the Block signal option (Attributes of signal heads).

3.  Into the Amber speed box, enter the desired speed (Attributes of signal heads).

Every second, block signals identify the status of their adjacent two blocks downstream:

• If a vehicle is identified in the next block, the signal switches to red. The block is closed for entry.
• If a vehicle is identified two blocks away, the signal switches to amber: A vehicle passing the amber signal (reduced speed area), is allowed the "desired speed". This speed is kept until the vehicle passes a green block signal further downstream.
• If no vehicle is identified in either of the blocks, the signal shows green: i.e. free passage at the desired speed specified.

If, by default, signal heads are assigned to a signal control, block signals treat them as delimiters. They are, however, not controlled via block signals.