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Signallers Avoiding Unnecessary Stop Aspects

Signallers have a vital role in delivering a safe and efficient railway. When it comes to SPADs, avoiding unnecessary stop aspects is the best way a signaller can help. Clearly, signallers are not in the business of stopping trains or holding signals at red without good reason. However, mistakes or oversights do occur and when operating in abnormal or degraded situations, this will stretch any signaller.

A review of SPAD investigation reports identified some examples of how unnecessary stop aspects contribute to SPADs:

  • A signaller tried for a second time to set the route but failed to observe that although part of the route had been set, the ground position light had not cleared and was therefore at danger. Following previous SPADs, local instructions had been introduced requiring signallers to set the whole route before clearing the starting signal. On this occasion the signaller tried to do this but failed to notice the incorrectly set points before clearing the signal. The result was that one of the intermediate signals was, from the driver’s perspective, unexpectedly showing a danger aspect.
  • A signaller wanted to speak to the driver and so kept the signal (that was later SPADed) at danger in the hope that the driver would make contact using the Signal Post Telephone (SPT). However, the signal did not have an SPT and the signaller could have determined this by checking the telephone concentrator (switchboard). 
  • A signaller had operated the wrong signal for the intended passage of the train. The signaller stated that he had been involved in a discussion with an adjacent signaller at the time of the incident, and this may have contributed to him being distracted and making the error. This coupled with the driver’s expectations about the signal sequence led to the SPAD.
  • A signaller had been attempting to find a margin earlier in their shift to accommodate some line blockages and had put the signal at danger anticipating that it would be used as a protecting signal. However, the signaller later decided to run a train before granting the line blockage but omitted to clear the signal beforehand.

The above examples highlight the importance of checking inputs to signalling system have had the desired outputs, checking assumptions, managing sources of distraction, and planning tasks effectively. These are examples of non-technical social, cognitive and personal skills that can enhance the way staff carry out technical activities, tasks and procedures. Further information on developing non-technical skills can be found on RSSB’s non-technical skills web page. Examples of non-technical skills and good practice for signallers’ relating to SPAD management include:

  • Keeping the number of times drivers are routed through loops, especially freight and On-Track-Machines to a minimum, as this can disrupt a driver’s ability to focus.
  • Avoiding calling a driver whilst train is running on cautionary aspects.
  • Clearing and replacing signals promptly, to give confidence to a driver that the route is set.
  • Pre-setting routes such that when a train clears the section, the route for the following train clears.
  • Only leaving or handing over their panel at an appropriate time, such as when all trains are either approaching green signals or are stationary.
  • The use of aide memoirs to maintain situational awareness.
  • Taking the lead in safety critical communications, especially if the driver is not following recognised practices for safety critical communications
  • Taking a supportive approach with drivers if they make contact seeking clarification about a route or shunting movement.

Furthermore, signallers need to be familiar with SPAD risks in the area they are working in. This means knowing which signals to keep clear as a priority—signals at the bottom of steep gradients, multi-SPAD signals or other signals that could be a high SPAD risk. Being able to confidently detect a SPAD occurrence is necessary as research confirms that SPAD indications are not always clear, and SPAD alarms are not fitted universally.  RAATS (Red Aspect Approaches to Signals) is a new tool that can also help identify potentially high-risk signals.

RAATS provides information on how often signals are approached at red.  As well as highlighting which signals are frequently at danger, RAATS data can help you identify the signals that are rarely at danger – when these signals do display a danger aspect, a driver may be caught-out by the unexpected restrictive aspects.  RAATS can also help map the differences between timetabled and actual operations, and provide insight on how well you have recovered from an operational incident, such as a failed train.  This is important as efficient operations tends to mean fewer red aspects.  As a starting point, request access the tool and check whether RAATS has information on your signals.

Further use of ‘acknowledged (safety) broadcasts’ is encouraged to avoid stopping trains to caution drivers where this can be avoided. Selecting an appropriate time for such calls is important so drivers dealing with restrictive aspects avoid becoming distracted at a critical time whilst listening to, and acknowledging the message. Clearly the call should not be so early that drivers risk confusion or forget details of the location.

Haven’t found what you’re looking for?
Get in touch with our Principal Human Factors Specialist for further information.
Philippa Murphy
Tel: 020 3142 5641
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