Great Western Express Signalling – A Brief Introduction

Written by: TrainSim-James

There are many intricate systems that train drivers have to master before being qualified to run out on the main, and none are more important than signalling.

In principal, signalling exists as a system used to regulate and direct traffic along the rail network, ensuring that trains are kept clear of each other at all times. The first timetables were a key step into the world of regulated rail travel, and as numbers grew for both passengers and freight, a plethora of varying systems were developed around the world, and today’s complex signalling makes trains one of the safest and most reliable methods of public transport to date.

The Great Western Main Line is equipped with the modern-standard British Signalling system, which has existed in its basic form since the days of the “Big Four”. As the GWML is being modernised for future Elizabeth Line services, the route is currently home to both old and new LED four aspect signals.

Unlike signalling in the US, which is predominately speed-based, UK signalling is typically route-based, where different signal aspects instruct the driver to either continue or brake accordingly for a cautionary, diversionary or stop aspect. All appropriate speed changes are handled exclusively by speed boards, not signals.

Below is the typical sequence of aspects when approaching another train.

  1. Green Aspect: Clear, proceed normally at Permissible speed*
  2. Double Yellow Aspect: Preliminary Caution, proceed expecting Caution at next signal
  3. Yellow Aspect: Caution, proceed and preparing to stop at next signal
  4. Red Aspect: Danger, stop.

*Permissible speed: the maximum speed of a certain section of railway line. Permissible speed indicators denote changes of the Permissible speed, the location of these indicators, and what they say, is information train crew are expected to know as part of their route knowledge.

A Signal outside Reading station, Signal No. T 1698 to be precise, displays a clear aspect (above), allowing the Class 166 driver to pull away. After they have done so, the signal will drop back to a danger aspect (below).

These four are the most typical signal aspects you will find on approach to an occupied platform or junction. It is standard practise to start braking as soon as you see the first cautionary signal (minimum of step 2 braking in the Class 166, step 3 or 4 in the HST, and whatever is required for the weight of a consist in the Class 66). You must never approach a stop aspect at more than 20 mph, we will go over why in a future article.

In the real world, drivers are expected to know the location of signals, and how they need to brake accordingly to come to a safe stop. Factors can range from train weight, distance between signals and inclement weather, so knowing your train and route is very important.

This type of signalling is called ‘track circuit block signalling’, only allowing one train to be in a block at any one time. If a train is standing on a section of track, it is completing that circuit and the signal immediately behind the train is set to red, the one behind that is yellow and so on. As the train moves forward, the signalling for any train behind clears to the next aspect.

A demonstration of the typical aspect sequence after a train has passed the signal in question, which in this case, is T 483 which stands on the Down Relief line at Iver station.

Defensive driving

In order to conserve momentum, especially in heavy trains that can take a lot of power to get going, it is recommended to employ defensive driving techniques when approaching a stop aspect. The trick is to crawl towards the signal for as long as possible, very gradually decreasing your speed in the hope that the signal changes to a proceed aspect, before having to come to a complete stop.

Another form of defensive driving is known as ‘chasing yellows’, this is where you approach a yellow or double yellow aspect and lower your speed enough to match the service ahead of you, consequently the signals change periodically as you approach them. While this can aid in keeping speed up and staying on schedule, it is important to remain vigilant; if the service ahead of you stops unexpectedly, you need to be able to still stop before the upcoming danger aspect.

Feathers and Route Indicators

The next step in learning the signalling is junction (or diversionary) signals. If the signaller has pathed you along a different route from which you are driving, a diversion, the signals on approach to the junction will forewarn you of the upcoming route change.

  1. Green Aspect: Clear, proceed normally at Permissible speed
  2. Flashing Double Yellow Aspect: Preliminary Caution, proceed initialising brake towards upcoming speed restriction as indicated
  3. Flashing Yellow Aspect: Caution, proceed, continue to brake towards speed indicated, expect feathered aspect at next signal
  4. Feathered Aspect: Clear/Caution, proceed expecting diversion at next junction as indicated by feather, drive in accordance with relevant signal aspect

This feathered route indicator tells the driver that they are diverging to the left under a double yellow ‘caution’ signal. Note that there are multiple possible feathers in some instances, each one corresponds with a different diverging route option. If no feather is lit, no diverging is expected.

The sequence of flashing yellow aspects indicates that a diversionary route is upcoming, tied with this is usually a speed board telling you what the speed will be at that junction, and so a brake application is required. At the end of the sequence, the feathered signal will display a series of white lights, these tell whether you are turning left or right (graphic provided demonstrates a left-hand turn). If you were pathed to continue, and not divert, these white ‘feathers’ will not be illuminated.

The feathered aspect will be accompanied by a proceed aspect, if this were yellow, it means that the next signal is red and you must prepare to stop, but it could also show green indicating that you are clear to continue on.

Another piece of information that can be given to drivers is through a ‘theatre’ route indicator. At places such as London Paddington, where there are multiple tracks and routes, the starting signal theatre can inform the driver which route they are pathed on such as ‘1’ for Track 1 etc. or on approach to a terminus, which of the many platforms you are cleared into.

A prime example of a ‘theatre’ route indicator, seen here on SN 5 at London Paddington. The Green aspect denotes clear, and the ‘1’ tells the driver which of the lines they will be routed down. This information is very important, there are so many lines out of Paddington that spotting which signal is yours can be a challenge – knowing your path can let you know where to look down the line.

Banner Repeaters

It is common for a drivers’ view of a main signal to be obstructed, be that because of where they stopped on the platform, or a sharp curve along the route. In these cases, banner repeaters are used to tell the driver what aspect the next signal is displaying. There are three states that modern banner repeaters can take:

  1. White Horizontal Banner: On, the signal it applies to is set at danger
  2. White Diagonal Banner: Off, the signal it applies to is set to a proceed aspect
  3. Green Banner: Off, the signal it applies to is set to specifically a green aspect

Two banner repeaters seen here at Ealing Broadway, both displaying a clear aspect, as correspondent with their respective signals. Both SN 2092 BR and SN 2091 BR (BR = Banner Repeater) are green, indicating that the paths beyond both SN 2092 and SN 2091 are clear.

Before the introduction of the green banner, a diagonal white banner could mean any proceed aspect from green to single yellow, but the added indication of a fully clear aspect allows drivers to pull away and know they can accelerate to Permissible speed.

Position Signals

Position (or Shunting) signals allow trains to move forward into potentially occupied sections, and are most commonly found guarding platforms, sidings and depot lines. They differ greatly from main signals, particularly as in a track circuit block, drivers know whether the next block is free or occupied, but when passing a Position signal, the section must be treated as occupied. This allows for the coupling of trains which would normally be limited to their own blocks.

There are a few types of Position signals:

  1. Subsidiary Signal: used in conjunction with a main signal for calling-on procedures
  2. Ground Position Light: typically found on standalone posts with no corresponding main signal
  3. Limit of Shunt Signal: a type of ground position light which can display ‘stop’ only

Two examples of ground position signals at Acton sidings, both are displaying a stop aspect. Note however that they are not specifically ‘limit of shunt’ signals, as they both have the capabilities of displaying other aspects.

Subsidiary signals display only a single aspect, two white diagonal lights. When lit1A, the driver has permission to pass the main signal regardless of its aspect. When the subsidiary signal is unlit1B, drivers must obey the aspect displayed by the corresponding signal. See, ‘Permissive Signals’ below.

Ground position lights can display either two white diagonal lights2A, indicating that shunting movements are permitted, horizontal white and red lights2B or two horizontal red lights2C that indicate stop, this is the furthest which a shunting train is allowed to proceed. Certain ground position lights may be fitted with yellow bulbs instead of red, these would apply only to movements in the direction to which the signal can be cleared, other movements can pass at caution at any time.

Limit of Shunt signals3 are a form of ground position light that is fixed to ‘on’, with no space for a proceed aspect, meaning all movements are not to pass this point unless authorised by the signaller.

Permissive Signals

Permissive signals are used when certain movements, that defy the block signalling method, are required. For example, if two separate DMUs are coupling away from the depot, such as at a station, or a locomotive needs to rescue another service, they must be allowed permission to enter an occupied block in order to complete their duties. This is the most common permissive signal procedure, and is governed by ‘Calling-on signals’.

Extreme caution must be adhered to, drivers should travel at speeds where stopping at a short distance is next to no issue, and under no circumstances should this need to exceed 15 mph.

T 1685 is displaying a ‘calling-on’ aspect; the block ahead is occupied, so the signal stays at red, yet the two white lights indicate permission from the signaller to proceed with extreme caution. Additionally, this signal is also fitted with a ‘theatre’ route indicator, telling they driver they’re going into Platform 9 at Reading station in this instance. Note that T 1687 is displaying a clear feathered aspect, while T 1689 is set at danger.

There is a lot of information in here, but all of it will we useful at some point when working the Great Western Main Line, so take the time to learn it if necessary, or just refresh your memory. We shall be covering safety systems and signage in a future article, so for now, make sure head to the Store, as Train Sim World: Great Western Express is available now!

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We’re always happy to receive your comments below but please ensure they are related to the subject of the article, we’ll remove any that appear to be unrelated.



  • Even though I am incredibly knowledgeable of the UK signals after playing for 2/3 years, it’s been nice to refresh my memory and learn a few extra things. However, I was thinking that for the people who don’t know the signaling system for a route, it might be handy having a dedicate page/screen or even an actual tutorial in game on how they work. For example, a page, like I said, or a tutorial like what was done for the Marseille – Avignon route in TS17. I know that there are a lot of people who wouldn’t think to vist this site in search of help so it would likely be useful to a lot of people. Another option could be a steam guide or even a link to this page but it’s something that I thought may be useful.

    • Thanks for the detailed comment Ant Craft, we’ve had several people asking for information in the game so it’s certainly something we’re looking into. Really pleased you found the article of use 🙂

  • This is absolutely the most detailed and comprehensible guide to signaling that I have ever seen for TSW or TS. I agree that this would be valuable in a user manual, but even better would be a tutorial. Is there one already or one in the works? (I’ve been away from my TS/TSW computer since late August, but will be returning at the end of this week, so please excuse my ignorance.)
    Tom Pallen

    • We are working on getting this information into the manual, Tom, it’ll get there eventually! As for any tutorials, there isn’t one included in TSW at present but I’m happy to relay this to the Development Team to look into but I cannot promise anything right now 🙂

      • Thanks, James. Now that I am back at my adequately powerful computer, I’ve started running GWE, beginning with the Class 66, which offers the one and only scenario dedicated to freight operations: “Aggregate Industries”. At the end of this scenario, the driver has to pick up a rack of hoppers after having unloaded them, dropped them off, and refueled the 66. The first challenge in this operation comes with finding one’s way back to the hoppers, especially since that efficient female voice doesn’t mention that this will involve a front couple (there is a symbol in the correct place, but getting there is challenging to say the least. I do like a challenge, but then comes coupling. On my first attempt, as the engine approached it, the last hopper began to shake and shimmy like a nervous virgin: a few small bumps but no coupling allowed. The correct action finally occurred, but only after I searched for and moved several pieces of equipment attached to the 66’s front. There’s no mention of coupling in the GWE manual and no tutorial on the subject. Are we really supposed to somehow intuit the correct procedure? A few more instructions within the scenario would have helped.

        • All the instructions for coupling with the Class 66 is included in the Drag Line scenario, Tom but we’ll pass your comments to the right people here to look into

  • Great article, would be nice to have this information available in game as a tutorial or reference menu. 🙂

    • Interesting idea iggl3p1ggle, will certainly get that noted down and passed to the right people to look into 🙂

  • Useful, interesting, practical … as always. Thank you, Trainsim-James.

  • Flashing yellows are not currently implemented in GWE. Does Dovetail plan to implement them in the near future?

    • Flashing aspects are part of the signalling in GWE Sam but, for some reason, they do not appear to work properly – only works on some signals and not others. The team are continuing to investigate why this is the case and it will be addressed once it has been traced

  • Will this ever be added to the manual? CSX got the same signal article, but that information was never added to the manual, and it is not immediately obvious to go to the TSW articles and page back a few months in order to get any information on how CSX signals work. Somebody who does not know of this site would be out of luck entirely.

    • We’re working on it Phillip, translating several thousand words into six different languages takes time when there’s so much going on, not to mention the other creative work that needs to be undertaken, etc. Please be patient, it will get there eventually! 🙂

  • I have never seen a yellow flashing signal in GWE for route changing, is this already implemented or WIP?

    • And by the way why dont you guys add this signaling guides to the manuals?
      The US signaling guide is still not in the TSW CSX manual. Nobody who is new to TSW will find this guides on the old articles here on this page.

      • We’re working on it Daniel, translating several thousand words into six different languages takes time when there’s so much going on, not to mention the other creative work that needs to be undertaken, etc. Please be patient, it will get there eventually! 🙂

    • It is implemented but doesn’t seem to be working as intended Daniel. Currently, it works on some signals and not others. The team are investigating and it is expected to be fixed in due course.

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