NIMBY supports two signaling methods, which we call block method and open track method. Block method is similar to real railroad signaling and uses blocks. See attachment for an overview and an example of real railroad signaling. It also explains basic concepts like blocks and junctions.

Open track method allows to combine multiple blocks by converting blocks into single-direction open track. Not all blocks can or should be converted into open track. Both methods can be used as required or desired in the same save.


Similar to IRL railroads, the track has individual blocks, with signals only allowing one train into each block. Track switches, crossings, etc. are considered to be outside any blocks and can be referred to as junctions.


Example 1 shows a railroad fragment (not to scale!) including blocks, junctions and signals. Blocks are track sections inside green boxes. Junctions are tracks between green boxes. Signals are placed at the end of the blocks. Arrows in this example show the possible direction(s) of travel.

Signaling here is very similar to the IRL railroad, as you can see if you compare this example to the one in the attachment. The only difference is related to the single track (bi-directional) line. NIMBY 1.16 signaling does not fully support bi-directional line operations. Details of bi-directional line signaling are in a subsequent section.

Block method uses one type of signal, called path signal.




The open track method allows fewer signals than the block method. This is achieved by combining multiple consecutive blocks and converting them into one open track section. Blocks can be combined if there are no junctions between them (or if the only junction is a diverging track). Using open track often means getting rid of most real-life signals.


An open track is a continuous piece of track, at least a block long (usually multiple blocks), where any number of trains can drive at the same time, without risk of collision. Open track allows travel in one direction only. An open track is similar to a one-lane highway or tram operation on sight.

An open track has an entrance and an exit. A balise (=track contact reader device) starts an open track. A path signal (or another balise) ends the open track.


Example 2 also uses the same railroad fragment as Example 1, but uses the open track method. Most (but not all) blocks have been converted into open tracks, marked purple. Many signals have been eliminated and balises have been placed at the start of each open track.



Bi-directional track signaling is the same as in Example 1, because open tracks must have a single direction. Thus, the single track line, middle track of the three track line, the terminus station and the depot tracks remain as blocks.

Station blocks are not usually converted into open tracks, because they are often bi-directional and typically to short for more than one train at once. Train stacking at stations is addressed in a subsequent section.

While possible, it's usually not practical to convert a single block between two junctions into an open track - it's simply too short to improve throughput. However, a block that is only as long as a train should not be converted into an open track - it could lead to delays or deadlocks.

Creating open tracks is not required. However, having fewer signals could speed up game performance.


All open tracks and many blocks are single-direction. Add a one-way signal to mark the desired direction. You only need to install this signal where trains exit the open track (block), and only if otherwise possible for trains to enter it the wrong way (e.g. a crossover or track split). One-way signal is like a "Do not enter" sign on the roads, and applies to the entire track between any platform and any switch. Thus one sign per open track (block) is enough, unless there are platforms inside it. A good location for the one-way sign is near the exit path signal.

Because trains can always reverse at platforms, you can add a one-way sign on the side of the platform trains should not exit from as a safety measure.


In examples 1 and 2 the arrows (which are really NIMBY one-way signals) were used to indicate direction of travel. Example 3 is the same railroad fragment and signaling as Example 2, but it now illustrates the minimum recommended placement of one-way signals (there aren't many!)

This is an overview of all NIMBY signals (1.16).

• Prohibits trains from operating on a track section in the opposite direction
  
• Applies to entire section between any platform(s) and/or switch(es)
  
• Place where trains exit from the one-way section (like "Do not enter" sign on roads)

• Ends platform inside a track segment (otherwise, the platform is the entire segment)
  
• Previously used to indicate exact train stop position on track (now done with advanced stops)

• Place to start an open track that allows multiple trains driving in one direction
  
• Do not use on bi-directional track - can lead to head-on collisions
  
• See explanation below on track reservations

• Place at exit from one block (open track) into the next (before any junction)
  
• Allows the train to proceed or stops based on whether the train's path is open
  
• Normal color is yellow ("unknown"). Turns red when a train is stopped.
  
• See explanation below on track reservations

• Limited use - mostly, to allow the second train into a station block in certain circumstances
  
• Use train stacking and multi-train platforms (and not this signal) in special cases discussed below

• Prohibits trains from operating on a track section in any direction
  
• Applies to entire section between any platform(s) and/or switch(es)
  
• Can be configured to apply only to trains or lines with selected tags, or alternatively those without selected tags
  
• Place near any entrance inside the restricted section

NIMBY railroads consist of blocks, open tracks and junctions. There are no signals in the middle of blocks or open tracks, and because sequential blocks can be converted into an open track, most signals in NIMBY are effectively placed around junctions.

• Identify junctions - places where tracks cross, merge, or simply get too close (closer than the train width).
  
  • Multiple track crossings, merges, etc. close to each other => combine into one junction. If a train cannot fit between two switches - that's all one junction.
  
  
• Signal each junction. See below.
  
  • You will also define where you have open tracks and blocks around junctions.
    
  • Bi-directional track (single track lines) can be signaled in alternative ways. See a following section.
  
  
• Optional: Split continuous track between junctions into blocks and open tracks as desired (e.g. for operational needs).
  
  
• Add special signaling arrangements. See our Automated Train Stacking guide.
  
  • Secondary platforms at stations
    
  • Stops for multiple vehicles
    
  • Train stacking (depots, stations)

1. Each track into/out of the junction: determine if it's open track or block, and direction of travel
   
   
2. Open tracks that start from the junction => place a balise to start an open track
   
   
3. Open tracks and blocks that end into the junction => place an "exit" path signal
   
   • If trains could enter them the wrong way also add a One-way signal. This is usually the case when there is bi-directional track inside the junction.
   
   
4. Single-direction blocks that start from the junction => rely on exit signals in #3. No other signals needed

Stations are no different than any other track. After signaling junctions, stations adjacent to junctions are already signaled. Depots in NIMBY are the same as stations.

• Station inside open track or block => one-way signal to prevent exit in wrong direction (if applicable). This is to prevent train route AI from reversing the train in a glue run (see below).
  
• Station next to a junction => place "exit" path signal or one-way signal on each track
  
• Station exits into a block => place a path signal at exit
  
• Station exits into an open track => place a balise at exit.

The example below is the same as for junctions, but signals are explained from perspective of stations.

Single-direction track needs protection only in junctions. This is because in NIMBY there is no hit-from-behind type collision (the faster train behind will slow down).

Bi-directional track also needs to be protected throughout its length, against head-on collisions and train deadlocks.

To prevent head-on collisions, track reservations from the path signals at the two ends of the bi-directional section must overlap, so they can detect each other. That is, there needs to be a stretch within the section that can be reserved by signals from both ends. As a reminder, track reservation extends from the path signal until the next same-direction path signal.



Because balises end track reservations from both sides, there is no overlap of track reservations. Balises should not be used in the bi-directional section.

The approach in the previous paragraph also substantially reduces, but does not eliminate the risk of train deadlocks. NIMBY signaling functionality in 1.16 cannot prevent deadlocks. It needs to be supplemented with a good track plan, timetable and trains operating on time.

To eliminate deadlocks, set an exit track from a bi-directional section. This is a track that can only be used to exit (not enter) the section and that any train can use.


Bi-directional track can be signaled as a junction, a single block, or two blocks (for each direction). Mixing is possible (e.g. junction in one direction and single block in the opposite). There is more detailed info about the different ways in the full guide.

Double track line junctions



Single track line joining double track line

Signaling tends to be straightforward and follows the same pattern. The key questions are whether station platforms are inside open tracks or have junctions on one or both sides, which tracks are single direction vs. bi-directional, whether there are stopping and passing trains, and whether train stacking exists.

Example station inside open tracks (i.e. no switches)



Examples (a) simple 3-track station with bidirectional middle track and (b) 4-track station with tracks for local and express trains (no reversals)



Example simple 2-track station on single bi-directional track line (passing siding) - one version with no reversals possible, the other where trains from the east can reverse



Examples (a) 3-track terminus and (b) 2-track terminus on a track curve




City stop signaling for two vehicles (trams, buses) in each direction



Terminal loop signaling

This information is provided as a supplement for a quick overview of IRL signaling. This is based on traditional blocks with signals in fixed locations, and is simplified. This section also explains a couple of basic concepts.


The illustration below shows a railroad fragment (not to scale!) including blocks, junctions and signals. Blocks are track sections inside green boxes. Junctions are tracks between green boxes. Signals are placed at the end of the blocks. Arrows show the possible direction(s) of travel.

• A block is simply a continuous piece of track where a single train is allowed to be located (drive or stand). A block should be long enough to allow a train to completely fit within the block and it does not include any switches (points, turnouts), crossings, gauntlets, etc.
  
  
  • Line block vs. station block. A line block is a driveable section on a railroad line. A station block is a track at a station where trains are expected to stand. Line blocks tend to be much longer as trains pass them at speed while a station block can only be barely longer than the length of a train.
    
  • Single direction vs. bidirectional block. This affects whether the block is intended for movements in a single direction only or both directions. Signals must coordinate with block directions.
  
  
• Junctions. These are areas where trains transition from one track to another through switches, cross other tracks, etc. Junctions are located between blocks. A junction may connect many blocks.
  
  
• Route. Routes are predefined track paths from one block through the junction to another block. Routes can also be unidirectional or bidirectional.
  
  
• Signal. Signals are used to permit trains to exit one block and enter the next. A signal should NOT be placed inside a junction, it should always be at the exit of a block - just like in a street intersection you stop the car in front of an intersection, not in the middle of it. Signals at or near stations are often called exit (from station) or entrance (into station) signals.
  
  Multiple signals may permit entering into the same block. For example, in a 5-track station, there will be 5 signals which may all allow to proceed onto a single main line block.
  
  A signal's normal aspect is red. It is switched to green in anticipation of an approaching train following its specific orders.
  
  
• Interlocking. Junctions (switches) and signals are coordinated such that a green signal from block A through the junction to block B is coupled with switches thrown to allow the train to move accordingly. Any other switches potentially in conflict will be thrown in a different direction.

Trams operate at slow speed and can stop quickly. As a result they normally operate on sight, without signals. Signals may be installed at intersections, similar to any city traffic.

In NIMBY tram signaling is no different from train signaling.