Railway signaling usually follows the red/yellow/green system (with exceptions):
- red: Stop / Warning; block ahead is occupied / obstructed
- yellow: Advance Warning: Block ahead is free, the following block is occupied / obstructed
- green: Line free at least two blocks ahead
Note that on German railways yellow is mostly not used in this way. See chapter German Signaling below.
In many cases signals fall back to and stay in the safe state, red. That is, after a train passed the signal it will fall back to red and remain red until a next train approaches and the following block is free. This system is sometimes referred to as "Closed Block".
Closed blocks are found within stations, in front of a branch or an automatic level crossing.
The "Closed Block" is Rocrail standard.
On main lines the line is commonly divided into sections (blocks) allowing multiple trains to follow each other. Fore safety reasons, e.g. to avoid rear-end collisions, Automatic Block Signaling (ABS) is used. Signals in ABS automatically return to yellow in case the block ahead is free or green in case (at least) the next two blocks are free.
Setting up an Open Block
In Rocrail an Open Block is formed by converting the previous block's main signal into the entry signal of the block.
In the above example blocks bk2, bk3 and bk4 were converted. To make bk2 an Open Block, the block properties of the previous block, bk1, are opened (e.b. by right clicking on the block symbol and selecting Properties… from the context menu). On tab Signals the check box Open Block is activated. Afterwards the appropriate "next block", bk2, is selected from the drop-down list:
Note that signal sg1 in block bk1 is thereby converted into the entry signal of bk2 and bk2 is the Open Block.
Accordingly in bk2 the next block is bk3, in bk3 the next block is bk4.
|There must be one "next block" only seen in the direction of the route: If the line branches two or more routes exit the block. Thus, there's not only one but two (or more) "next blocks". In this case an Open Block is not suitable.
Special Case: German Railway Signaling
On German railways yellow is mostly1) not used in the way described in chapter General: In the common H/V signaling system (see Signaling for details) yellow (green plus yellow) is referred to as Hp2 and indicates a speed reduction (to 40kph unless otherwise stated) due to one or more thrown switches in the route behind the signal.
Hp2, therefore, is not an advance warning and must not be used as such.
| Schematic representation of a German colour light signal
in the H/V signaling system showing Hp2, reduced speed
In the example below Rocrail was used in standard configuration:
To avoid the wrong usage of Hp2 in this case the following option in Rocrail must be activated: Green aspect if next is red.
With this option active the signal correctly shows green (Hp1):
Open Block on German Railways
The "Open Block" on German Railways is another special case. For ABS (e.g. the so called "Selbstblock") block signals are used. These are two-aspect signals displaying either red (Hp0) or green (Hp1) only. Signals with more than two aspects must not be used on main lines with ABS.
| Schematic representation of a German two-aspect colour light signal
in the H/V signaling system showing Hp1, line clear
No special settings for "Open Blocks" on German railways are required. Using two-aspect signals is the only prerequisite:
|Wrongly displayed Hp2 in bk3 with three-aspect signals (top) and correct Hp1 in all open blocks with two-aspect signals (bottom)