While we all deplore the injury and suffering caused by the Ladbroke Grove train crash, as engineers we must try and learn from it. While studying the clear diagram shown in your article (NCE 14 October) I was struck by the inconsistencies of the track design.
A train travelling along 'down' line 4, crossing over to 'down' line 1, leaves line 4 at 2, switches onto line 3 and approaches signal SN109. If the 'up' line 2 is busy, the train should stop at 'red' on SN109.
However it overshoots.
It approaches points at 4, which are of course interlocked with SN109 red, and thus the train continues on line 3.
There are now apparently three options facing the track designers:
Run the train into a sand trap: This is apparently now illegal for passenger trains.
Run the train back onto 'down' line 4: It is unlikely to collide with an overtaking train on line 4 owing to standard spacing between trains, but could possibly collide into the rear of a slower or stationary train further down line 4.
Run train onto 'up' line 2: Highly likely to collide with an 'up' train, since the reason SN109 was at red was because line 2 was already occupied by an 'up' train. From the diagram shown, there would appear to be no route for the train now travelling 'down' the 'up main' line 2 to get back onto the 'down main' line 1, for at least 1km.
Given these options, why was the track configured according to option 3, which had a higher probability of collision, with twice the likely closing speed and four times the kinetic energy release of a collision in option 2?
The design for a signalling system should recognise the possibility of driver error, and the arrangement should be such as to mitigate the failure. Surely such an approach would dictate that where signals controlling a line switch are passed at 'red', then the points interlocks should be such that the overshooting train is returned to the line from which it came, or at very least to a line travelling in the same direction.
Peter A Cracknell (M), 34 Cedar Road, Berkhamsted Herts, HP4 2LB
Profits came before safety
I was disappointed to read your bland editorial on the Paddington rail crash (NCE 14 October), especially the statement: 'It is also too easy to say the crash was a result of rail privatisation, although the new regime has created significant problems.'
I hope the ICE will be as forthright on the issue as the representative from Transport 2000 who, when asked by the cross-party transport committee of MPs whether profits had been put ahead of safety, said: 'I think that they have. Particularly if you look at Railtrack and the train operating companies. They are much more interested in promoting their companies' profits and share price. What has shattered public confidence in the last 10 days is the feeling that the railways aren't as safe as they should be.'
I agree with the passenger groups who have called for
Railtrack to be stripped of its safety role to restore credibility,
and the pressure group Save Our Railways which wants an accountable and independent safety system. There used to be an effective one before privatisation.
Paul Donnachie (M), 7 Lowther Road, Norwich, NR4 6QN
Fighting the phantom image
While reading the numerous articles on the recent Paddington rail tragedy, I realised the similar danger facing train drivers and motorists during periods of bright sunlight. I am referring to sunlight shining into the signal head lenses, reflecting off the rear reflectors back through the coloured lenses giving the visual impression that the signal is lit.
This is known as phantom image and raises concern for all transport users where light signals are used to control conflicting movements at intersections.
The recent development of light emitting diode technology has seen the introduction of LED traffic signals capable of satisfying the high standard light output and exceeding the highest anti-phantom requirements of UK government specification.
The new LED traffic signals virtually eliminate the phantom image and, when lit, considerably improve the conspicuousness of signals, giving a clear and sharp signal in a wide range of weather conditions.
Bristol is the first UK city to trial the new red, yellow and green traffic signal heads. The introduction has shown a significant improvement over existing tungsten halogen lamps with benefits which include:
improved optical efficiency showing a clearer signal across the whole aspect;
considerable energy savings with the LED using 17 watts compared with the normal 50 watts;
reduced maintenance costs as there are no call-outs needed for lamp replacements during the life of the lamps; and
increased working life from six months with tungsten halogen to 10 years quoted for the LED lamps.
So why isn't everyone rushing out to buy these lamps? Cost. At the moment the R&D costs are still high and to be recovered, but as soon as the lights are produced in their millions the reduction in cost will ensure their cost effectiveness.
I firmly believe LED signals will improve road safety. I also believe the railway network will benefit by retrofitting their red lamps with LEDs.
John Laite (M), 15 Parnall Crescent, Yate, South Gloucestershire, BS37 5XS