During the last decade we have introduced a variety of LED signals that provide a long and reliable operational service. The very low failure rates (over 40 million fault free operational hours for GPLs) and slow degradation of the LED intensity, allowed our design engineers to consider how to design the next generation of signals. The next challenge was to enable the industry to benefit from the signal performance and reduce the whole life costs and operational risks even further.
We set out to design a range of signals that would be maintenance free - never needing a scheduled maintenance visit this reducing the time that staff were on the operational railway. We also aimed to reduce the need for heavy structures with load bearing capabilities for maintenance personnel, and massively reducing the network maintenance costs and the safety costs incurred in going trackside.
Our experience told us that we could develop highly efficient and reliable circuits and we knew that the existing annual maintenance was mainly limited to cleaning the lenses, therefore we concentrated on the light output parameters and maintenance cleaning requirements. We would aim to develop a ‘self cleaning’ signal.
The project as a whole has been running for over a decade, starting with the development of ranges of LED Colour Light Signal (CLS) signalling that were designed to retro-fit on to existing infrastructure in the same ‘format’ (with housings that were similar to the filament signals) through lightweight versions to the current iLS (integrated Lightweight Signal) which is a radical development featuring the signal head and post being integrated into a single Glass Reinforced Plastic housing and post, with a trunnion/enclosure base.
The original (now referred to as the Classic) LED Colour Light Signal was created using a spherical polycarbonate outer cover under a protruding visor. The development of this technology led to the curved and angled front face of the modules now used in the iLS which has in September 2015 been accredited by Network Rail as ‘self-cleaning, maintenance free’.
Our team has vast experience of optical design and were already familiar with polymer technologies from our products developed for the highways market. These techniques had not been applied in the Rail Industry and we therefore decided to build prototypes to demonstrate our logic to key industry partners, with the aim of gaining their support.
The innovation in this development came from understanding the signalling specification, coupled with our many years experience of operating in the rail environment and understanding where we could develop the product without compromising performance.
Our Rigorous Testing
Our controlled tests showed us that by using UV stable polymer lenses, combined with a hydrophobic hard coating, we could reduce the tendency for dirt to adhere to the lenses and degrade the appearance of the aspect.
Our experience showed that this alone would be insufficient and we designed an outer cover arrangement that would position the outer exposed surface in greater contact with weathering, thus promoting ‘self cleaning’ with the wind and rain action.
In order to use the action of the wind and rain to assist with the ‘self cleaning’ concept, we had to reduce the length of the visor, but had to maintain the length of effective visor.
The addition of an internal mask, reduced the amount of light entering and exiting the signal optics where sunlight could be reflected back towards a driver. We also angled the aspect beam downwards, further reducing the affect of potential signal phantom aspects.
This combination of solutions allowed the aims and objectives to be met, by altering the signal’s profile, it promoted self cleaning in a novel way that had not previously been done before. (It also has the benefit of reducing snow build up on the signal aspects).
As a result of this innovation:
Network Rail has amended its maintenance requirements of these signals as follows:
- Unipart Dorman iLS and CLS LITE signals now are designated ‘self-cleaning’ and require no visits for signals in locations where they are exposed to free falling rain.
- All other LED and filament signals on the network have an annual maintenance visit cycle.
Since the introduction of the Unipart Dorman LED signals, over 110,000 LED modules are now installed on the UK rail infrastructure, and the September 2015 Network Rail ROSE NR/SIG/10665/Mod 001 document now means that a significant number of them no longer require annual maintenance visits, driving increased savings and increased safety through fewer workers being required at the trackside.
Previously these signals would have required an annual check, involving a minimum of two track workers. With the new maintenance standard, we are removing the need for these visits, reducing the cost of ownership of the signal to the purchase and installation cost.
It is estimated that the 1000 filament Colour Light Signals which have been replaced by Unipart Dorman signals will be reducing maintenance costs be over £4,061,000* over the fifteen years of their projected life, and with a further circa 1000 to be installed in CP5, these benefits will double.
Additionally, there has been no Unipart Dorman signal failures in operation. Filament signals previously accounted for 72,000 delay minutes, equating to a cost of £2,775,000* annually which will be eliminated once all filament lamps are replaced.
These significant cost savings are being delivered now as a direct result of Unipart Dorman’s LED signalling innovations.
* Calculated on 2005 values using RPI to estimate current costs.