7.2 Signals, Trackside Signs & Whistle Boards
Key Takeaways
A colour light signal is at danger when it shows a red aspect, and a red semaphore signal is at danger when its arm is horizontal.
Trains normally stop at a signal at danger, but in some situations a driver can be authorised to pass a signal at danger, so a red signal does not make you safe.
Automatic and semi-automatic signals are identified by signs on the post and cannot always be put to danger by the signaller; some have a signal post replacement switch.
Distant signals have no red light, so trains will not stop at them; yellow semaphore signals are also distant signals.
Drivers sound the horn at whistle boards only between 06:00 and 23:59, except in an emergency or when someone is on or near the line, so never rely on whistle boards for warning.
7.2 Signals, Trackside Signs & Whistle Boards
Signals and lineside signs are written in a visual language that drivers read at speed. As a PTS holder you need enough of that language to understand where trains can go, to identify your location, and to avoid being misled into thinking you are safe.
Signals (PTS Handbook Section 1.3)
Most running lines have signals to control the trains. Generally, signals are operated from a signal box and carry an identifying number; there are also in-cab signals on some routes. Signals are usually attached to posts beside the track, but they can also be on overhead gantries or on the ground. Modern signals tend to use coloured lights, but some lines still have semaphore signals.
Colour Light Aspects
Each colour light signal shows an aspect:
| Aspect | Meaning to the driver |
|---|---|
| Red | Danger: stop |
| Single yellow | Caution: be prepared to stop at the next signal |
| Double yellow | Preliminary caution: the next signal is showing a single yellow |
| Green | Clear |
- A colour light signal is "at danger" if it is showing a red aspect.
- A red semaphore signal is at danger if its arm is in the horizontal position.
Do Not Rely on a Red Signal
Normally trains will stop at a danger signal, but in some situations they can be authorised to pass a signal at danger. That is why HB1 and the PTS handbook tell you, when walking alone, never to assume you are safe just because a signal is at danger.
Automatic and Semi-Automatic Signals
Some signals are automatic or semi-automatic and cannot always be put to danger by the signaller. They are identified by signs on the post: an automatic signal has a plate with a black horizontal band, and a semi-automatic signal has a similar plate marked SEMI.
An automatic signal may have a signal post replacement switch (SPRS) on or near the post, which can be used to put the signal to danger. Rule Book Handbook 2 explains that SPRSs are provided at some automatic and semi-automatic signals and are not always on the post itself. You may only operate one if you have the key and are competent to do so, and if you use one in an emergency you must ask the signaller's permission before restoring it (see section 8.2).
Distant Signals
Be aware that some colour light signals don't have red lights, so trains won't stop at them. The same is true of yellow semaphore signals. These are called distant signals: they warn the driver about the next signal rather than stopping the train.
Signals Do Not Protect You
Signals control trains; they do not protect people on the track. A train may be authorised past a signal at danger, may be routed across points onto your line, may run in the wrong direction during single line working, or may be an engineering train moving within a possession under the authority of an engineering supervisor rather than lineside signals. Signals also depend on train detection by track circuits or axle counters, which is why the PTS handbook warns that metal objects placed across the rails can change a signal aspect in front of a driver. Your protection is always the safe system of work, never the colour of a nearby signal.
Why Signal Numbers Matter
Signal identities are quoted using the phonetic alphabet and numbers spoken one at a time, for example "mike papa one four zero". A signal number is one of the quickest ways to tell a signaller exactly where you are, and many signals have a signal post telephone (section 7.3).
Limited Clearance and Telephone Signs (Recap)
- Limited clearance warning sign (red-and-white board, or yellow warning triangle sign): no position of safety on that side of the railway for the length of the structure.
- No refuges warning sign (blue-and-white board, or yellow warning triangle sign): no position of safety on that side, but positions of safety or refuges on the opposite side.
- Prohibition sign ("No safe access while trains are running"): do not pass while trains are running unless carrying out emergency protection.
- Telephone signs (a black cross on white for a lineside phone, black-and-white diagonal stripes for a signal post telephone) are explained in section 7.3.
Section 1.3 explains these signs in detail.
Whistle Boards
A whistle board is a lineside board, typically marked with a letter W, telling drivers to sound the horn. Network Rail uses them mainly at footpath crossings where pedestrians cannot see approaching trains.
- Drivers sound the horn when passing a whistle board between 06:00 and 23:59.
- Between midnight and 06:00 (the night-time quiet period), drivers do not sound the horn at whistle boards, except in an emergency or when they see someone on or near the line.
Warning
Never Rely on Whistle Boards for Your Protection A whistle board warns crossing users, not track workers. At night trains pass whistle boards without sounding the horn, and noise from plant, wind or traffic can drown out a horn at any time. Your protection is the safe system of work your COSS has briefed.
Speed Boards
Permissible speed indicators beside the line show the maximum speed for that stretch of line. Temporary and emergency speed restriction boards mark places where trains must slow down, for example after track work. Speed boards tell drivers what to do; they do not protect you. The maximum speed you need for your position of safety comes from the Sectional Appendix and your briefing, not from guessing what speed a train is doing.
Possession and Worksite Boards
Inside an engineering possession, possession limit boards mark the limits of the possession and worksite marker boards mark the limits of each worksite. The engineering supervisor authorises and controls the movement of engineering trains and on-track plant within the worksite, giving the driver or machine controller instructions about where to go and at what speed. If you are working in a possession, your briefing will tell you where these boards are and which lines remain open.
When is a colour light signal said to be "at danger"?
When it shows a double yellow aspect
When it shows a flashing green aspect
When it shows a red aspect
When it has no lights showing at all
When do train drivers sound the horn at a whistle board?
Between 06:00 and 23:59; at night only in an emergency or when someone is on or near the line
Continuously, 24 hours a day, at every whistle board
Only between 23:59 and 06:00, to warn night-shift track workers
Never, if any track workers in orange clothing are nearby
A signal post carries a plate with a black horizontal band. What does this tell you?
The signal is a distant signal with no red light
There is a lineside telephone on the post
The signal is permanently out of use
The signal is automatic and cannot always be put to danger by the signaller
Sections you finish are checked off in the contents.