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17 Jun 2002
Exclusive by Phillip Hill
The number of train crashes in the UK could be reduced if the country's rail operator, Railtrack, shifts the yellow color used in signals more towards yellow frequencies and away from the red.
The International Commission on Illumination (CIE) has been pushing for six years for the change, but Railtrack has not taken up the recommendations.
Last year's fatal crash at Paddington in the UK which killed 31 people highlighted the number of "signals passed at danger" (SPADs) and an official government report on the accident concluded that the driver could have misinterpreted rather than missed a red signal.
Railtrack standards for the color of signals are based on a British Standard (BS 1376) which is now 26 years old. CIE said bluntly in 1994: "The present CIE recommended yellow color area extends too far toward red." It called for the "substantial re-definition of the color domain for yellow". The CIE devised the internationally-recognized chromaticity diagram that has stood the test of time since 1931. The body's recommendations would move the yellow permitted for train signals considerably away from red. The current position for yellow in the British standard was probably because of the desire to encompass "amber" road traffic lights.
Graham Morris, head of corporate standards at Railtrack, told Opto and Laser Europe (OLE) magazine that Railtrack had done some work on the subject. "But we have to negotiate with the train operators," he said. "Their drivers are used to one yellow. They might be confused if another was introduced."
But a spokesman for ASLEF, the union whose member died in the crash, said that the subject had not been taken up with them. "It has never crossed our desks," he said. "We have never been informed of anything like this."
And Phil Dee, safety officer of RMT, another train drivers' union, said: "A brighter yellow would make it easier to pick up earlier. I am not aware that this has ever been discussed."
Another phenomenon could also be confusing train drivers. Peripheral vision will not identify color clearly. There are two kinds of light-receptor cells in the eye: rods and cones. Cones are responsible for color vision; rods give vision only of shades of grey. But beyong an angle of five degrees from direct viewing, the number of cones drops dramatically leaving an overwhelming preponderance of rods. Speed and a danger light not in the centre of vision would increase the chances of confusion.
The HSE report into the Paddington disaster highlighted the unusual design of signal 109 passed at red. "Instead of being placed one above the other as normal," the report states, "the lights on the gantry were arranged like a backwards 'L' with the red light over to one side - it would not have been at the centre of the driver's vision as he looked at the signal."
Stephen Westland at the Color & Imaging Institute, University of Derby, told OLE that confusion could occur because there were three types of cone to recognise blue, green and red. The proportion of such cones varies as one goes out from the centre of the eye. Here there are few or no blue recognizing cones so that red appears amber.
It is easy to experience the effect. Driving through a set of traffic lights on green, a motorist will see the red signal on the other road fleetingly as amber out of the corner of the eye.
Color confusion is so important that Westland is currently working on a UK ministry of defence project to ensure that fighter pilots cannot mistake colored cockpit lights.
On the UK railways, there are about 700 SPADs on average a year. Railtrack has identified 22 signals across the UK which accounted for a disproportionate number of SPADs from 1990 to 1999. Railtrack says that during every incident the signal was working properly and showing the correct aspect, in other words red.
Story courtesy of Opto and Laser Europe magazine. For more information on this story, contact Phillip Hill (phillip.hill@ioppublishing.co.uk)
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