Phantom Signals, a ghost of the past…

Do you want to learn more about the latest Anti Phantom Colour Light Signals (CLS)?

Phantom aspects are where an unlit signal appears to be illuminated due to an external light source. The ‘searchlight configuration’ of Unipart Dorman signals means they achieve immunity on normal single red, yellow, green aspects by always having one colour lit, but when an upper yellow module is added, difficulties arose when this module wasn’t illuminated.

External light sources such as low winter sun or even reflections from the curved windscreens that are currently used on new trains could cause the module to appear to be lit.

Following a national inspection of approximately 500 signals carried out by Peter Williams (Engineering Expert and Technical Fellow at Network Rail), incorrect alignment was found to be the significant factor, so the Unipart Dorman team worked closely with Peter, and Atkins Rail Ltd to define alignment techniques to minimise the risk of a phantom aspect. Unipart Dorman also worked closely with OptiConsulting Ltd, to characterise the improved phantom performance via laboratory tests and readability testing.

A ‘Noticeboard’ instruction to check vulnerable signals was issued to maintenance technicians and testing and maintenance standards and manuals have been updated with this new guidance. Since this instruction was published, reports by drivers of poorly lit or phantom aspects has dropped significantly.

Simon Wetherill of Greenlight Signals Ltd has been contracted by leading training provider Signet Solutions to deliver a signal alignment training course based on the new guidance. This new signal alignment course is in addition to the onsite product awareness sessions delivered by Unipart Dorman and involved collaborating on the curriculum and then setting a number of signals up in the quadrangle at Signet Solutions’ Derby training centre for students to carry out practical alignment exercises.

New resignalling projects along with the introduction of more trains with curved windscreens resulted in feedback that even with the optimal alignment, the top yellow still appeared to be lit on a very small number of signals in certain rare conditions, mainly in the South of England.

It was apparent an engineering solution for these challenging signal locations was needed and in collaboration with Peter Williams, a new design for top yellow modules was developed.  The new design combines new internal masking to reduce reflective surfaces within the module and a smoke tint instead of a clear outer lens, which capitalised on the success of similar Unipart Dorman products developed for the North American market.

Following extensive off track testing, four trial sites were selected based upon repeat phantom issues in early 2021 and there have been no further instances since. This modified module is now fully accepted for use by Network Rail and is commonly known as a Mod C module. 

The new design delivers an increase of 63% in phantom resistance when compared to a pre-Mod C module.   Switching to the new Mod C Module couldn’t be easier,  the plug-coupled device takes just a couple of minutes to changeover.

A new Mod C module was recently specified for a signal in South London where early morning sunlight caused a phantom aspect and a wrong side failure. It was supplied and delivered to site within days of the customer placing the order and its simplicity of fit allowed the concern to be resolved immediately and normal service was resumed without further incident.

There is no requirement to retrofit signals unless they are known to suffer specific sunlight issues that cannot be resolved by correct alignment, but this new module is a powerful tool added to Network Rail’s armoury to resolve top yellow phantom aspects.

These initiatives have significantly reduced the risk of phantom signals and all new 4 aspect iLS and CLS LITE signals are now supplied with a Mod C module as standard.

Peter Williams commented: “I am delighted in the way Unipart Dorman have responded to the challenge and the results speak for themselves”.

High Barton commented: “This is an excellent example of engineering innovation and implementation. We are pleased to support this initiative”. 

Simon Weatherill commented: “The signal alignment course was a great success mostly down to the collaborative approach that was taken”.

*The image used to illustrate this blog was taken during the readability assesment process for the Mod C module.

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