Light Rail for better public transport
Making LRT systems safe — Part Three, Article from the December 1998 edition of Tramways & Urban Transit
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Light Rail Transit Association
Light Rail for better public transport |
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Making LRT systems safe — Part Three, Article from the December 1998 edition of Tramways & Urban Transit
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Major Christopher 'Kit' Holden has been the public image of safety for promoters, builders and operators of 'new generation' light rail for many years. Now retired from the Railway Inspectorate, and a busy consultant, he explains how the modern safety regime has evolved.
In many ways the most contentious issue in the renaissance of street-running tramways in the UK has been that of the vehicle. Because both the Manchester and Sheffield Special Acts had stipulated that plans, etc. had to be submitted to the Secretary of State (in practice Her Majesty’s Railway Inspectorate - HMRI) as part of the approval process for the vehicle, the Inspectorate were able to start with a clean sheet when drawing up the requirements which had to be met. On the other hand it was well aware of the type of vehicle being produced in Germany and had practical experience of the vehicles used on the Tyne and Wear Metro and on the Docklands Light Railway, both of which were rooted in the modern, continental, tramway tradition. The accusation has often been levelled at the Inspectorate that it is responsible for the high cost of modern trams as opposed to that of buses because of the safety features which it requires to be provided. It is hard to see how this accusation can be fully justified in that it is the promoters who choose the vehicle they desire; all that is required of the Inspectorate is to determine whether or not that choice is acceptably safe. If the manufacturers and the promoters had thought a little more carefully about the safety implications of their proposed designs, in particular the internal fittings, then much costly retrospective work would have been avoided. Subject to my usual caveat that the views expressed are my own, I will endeavour to show what, how, and why the requirements for modern trams in the UK arose. I also discuss some of the operational matters on which a formal view has been taken.
Unlike the infrastructure, which was well heralded in the PGN (Provisional Guidance Note on the Highway and Vehicle Engineering Aspects of Street Running Light Rapid Transit Systems - April 1989) requirements for vehicles and operations, apart from individual decisions made for the Manchester vehicles, were not set out in any detail until the Symposium on Light Transit Systems, organised by the Institution of Civil Engineers and held in Nottingham in March 1990. To a certain extent the shopping list was based in part on HMRI’s experience in approval of modern rolling stock for the London Underground, Tyne and Wear Metro and Docklands Light Railway, in part on discussions held with the GMPTE planners, and in part on the answers to questions put by GEC and Firema whilst they were designing and building the first generation of vehicles for Metrolink. However as a basis the Stadtbahn ‘B’ vehicle was used as a role model.
The safety requirements for a vehicle can be grouped in a number of different ways; the first being a very broad division between those aspects which affect the people on the vehicle, that is the driver and passengers, and those which affect outsiders, that is other road users. Within those two broad divisions there are the individual systems on the vehicle such as lighting, traction and braking, access controls, etc. Perhaps the most appropriate place to start is the external appearance of the tram, and I am not here considering the livery which, except under the most bizarre circumstances, falls well outside HMRI’s ambit. The first essential was that the vehicle should shout ‘tram’ to all other road users, particularly at night. Hence the concept of the lighting scheme with a triangular formation of headlights which should be lit day and night. The outline of the tram also needed definition and so the lights required for Large Goods Vehicles (LGVs) were also necessary; front and rear position markers to use the phrase in the Road Vehicle Lighting Regulations, side and tail lights to ordinary mortals. Similarly it seemed sensible to provide the side markers required of LGVs but not necessarily their spacing. Turn indicators also fell into that category, but what was to be done to warn other road users who were alongside the tram that it was about to turn. The simple answer was to make the side markers flash in sympathy with the indicators. In Manchester it was arranged to flash these off at the same time as the indicators flashed on. A better solution was found for Sheffield by using a dual-filament lamp, as for the combined stop and tail light on a car, for the side marker; the higher wattage filament being arranged to flash in time with the indicators whilst leaving the low wattage filament on continuously. It is not permissible to show a red light facing forward or a white backwards. This applies equally to reflectors and hence, for a double-ended tram, all were persuaded, not without some argument, that amber reflectors all round, at the ends as well as the sides, were the correct solution.
The second main consideration was injury prevention if possible but failing that minimisation. Externally that meant fendering all round, including side under-run protection as for LGVs. Accident histories from Blackpool showed that, in a significant number of instances, the drop-down tray was causing injury rather than preventing it; it was not even clear that it was contributing to the prevention of fatalities. A second consideration, that of the likely consequences should a drop-down tray drop during high speed running on the ballasted sections of Metrolink, reinforced the view that the risks attached to persisting with the requirement to fit such trays outweighed the benefits and an alternative solution was sought. The particular design of the Firema bogies led to the concept of a fixed deflector which has proved, in the event, to be highly effective. Later schemes have found similar but not identical solutions. The replacement engineering vehicle for Blackpool broke with tradition and has deflector scoops fitted and not drop-down trays.
I, personally, had always viewed with disfavour the battering ram which was the standard coupler on the Stadtbahn ‘B’. At the time it was not possible to obtain an automatic, folding or retracting, coupler; you could have one feature or the other but, despite one manufacturer’s claims, not both. Not only would the coupler have to be stowed behind the fender line but also when it was deployed the skirting forming the pedestrian protection at the ends of the Firema vehicle would have had to have moved out of the way automatically. Metrolink claimed that only the provision of an automatic coupler would enable them to meet their planned working time-table. They also claimed that removal of skirting panels and their subsequent stowage and the manual unfolding of the coupler could not be performed safely away from the depot. Nevertheless the Inspectorate insisted that sufficient stowage space for retrofitting a folding coupler was retained on the Phase 1 trams for Metrolink. I am pleased to note that it is planned that the couplers for Phase 2 trams will be retracted behind the front fender when not in use.
Injury prevention on the inside of the passenger saloon and driving cabs was to be secured by careful attention to details of glazing, seats, handrails and other fixings. Metrolink’s trams, being high-floor throughout, did not have the problems of internal steps which subsequent, partial low-floor trams have. Such steps have led to injuries, particularly to elderly passengers falling down during sudden braking. Stairways from the top deck of a double-decker have always had to make at least one 90° turn and this is a technique which has been followed in the Midland Metro tram where the door layout makes this reasonably easy to achieve.
Whilst the smooth control of traction is relatively easy to provide, the required braking performance is not. The dual requirement for a high brake-rate and a low jerk-rate is well-nigh impossible to achieve if the brake-rate has to meet exactly the same numerical standard as that for private cars. It is doubtful that PCVs (Passenger carrying vehicles) ever deploy the full, emergency brake-rate of which they are supposed to be capable; if they did so then most of the passengers, particularly the standees, would join the driver in his cab. In the end a pragmatic approach was adopted which, in effect, said ‘provide the best braking performance that you can combined with limiting the jerk-rate to less than 1 m/s3 in normal service and the operators will have to be taught defensive driving techniques which will enable them, within the traffic environment at the time, to stop short of the vehicle in front’. Most modern trams have a regenerative braking system which, providing the line is receptive, allows electrical braking down to a certain speed. That speed is dependant upon the precise electrical arrangements but is seldom below about 8 km/h. Regenerative electrical braking, as provided in the present vehicles in operational use in the UK, has one other weakness in that, because it is dependant upon the rotational speed of the motor it becomes less effective as the motor slows down. Hence at some stage mechanical braking has to be blended in. The latter also has to cater for the case, even when rheostatic braking is available if the line is not receptive, when the electrical system fails completely; that is with the exception of fly-wheel driven trams which can use regenerative braking at all times except for the rare occasions when the fly-wheel is already rotating at maximum speed whilst the tram is moving.
Whilst the door design itself is not specified, only that the edges should not present a hazard to passengers when opening or closing, the door controls have excited a fair degree of discussion. The normal controls should now all comply with the Rail Vehicle Accessibility Regulations 1998 in their shape, size, and style. However the problems arise from the emergency door opening methods and where these should be sited. The task is simple; they should be readily accessible to all but the ill-intentioned! If they are put at a height suitable for wheel-chair users they are at fiddling height for the 5 to 10 year-olds. If they are put over or in the door header panels, only the tallest 15%ile can reach them. They must also be arranged that if one is used it must be obvious to, and only able to be reset by, the driver. They must also be interlocked with the traction and braking controls so that when the doors are able to be opened by hand the tram is at or nearly at a stand; I was able to open the doors on the Sheffield vehicle on trial on the Rheinbahn whilst it was travelling at speed. Crew access doors are an equally contentious issue. I believe that the driver ought, particularly on a street-running system, to be able to enter and leave the driving cab without having to pass through the passenger saloon. It is not good practice to have to force one’s way past closely-packed passengers to use a point iron on an incorrectly set and failed pair of points. Neither is it good practice on those systems sharing an alignment with a main line railway to have to scrummage around in a locker in the saloon to extract such emergency equipment as a red flag and detonators.
An operational requirement is to have an effective audible warning device. The purists all felt that the traditional bell was the correct device, but there are a number of good reasons to question this. Firstly it was necessary to provide a sound which was effective at long range for segregated running as well as a less potentially harmful sound for on-street use. Secondly, modern electronics can be made more reliable than a mechanical device such as a trembler bell; the single stroke bell or gong did not seem to be a robust enough sound for today’s traffic conditions. Thirdly and not the least significantly, there was a desire to demonstrate that there had been a fundamental change from the image of the traditional tram to its very different modern counterpart and to get away from the mental image that people had whenever the word ‘tram’ was mentioned. In discussing this problem one evening with the GMPTE staff a half jocular remark was made that an A4 chime whistle might fit the bill; the rest, as they say, is history. In view of the fact that it was also necessary to provide for long range lights as well as the dipped headlight regime for on-street running it was arranged for both the lighting and the audible warnings to be changed from on-street to segregated through a single switch; in Manchester this switch also changed the traction controls from limiting the speed to 30 mile/h on-street to maximum permitted on segregated running.
The requirement imposed by the Parliamentary Acts for a tramway to be approved before it could be opened for traffic, one suspects, was conceived as applying only to the physical aspects of the tramway. However, as one lawyer well known to tramway enthusiasts expressed it, when has lack of powers ever stopped the Railway Inspectorate from taking action when it thought it was appropriate. It was therefore decided that the ability of the operating company to run the tramway safely also fell within the approval process. So from the beginning the selection and training of all the operating and maintenance staff was subject to inspection. Driver training and the issue of an authority to drive (a licence) was particularly scrutinised because the Department of Transport was persuaded that, following the traditional tramway practice of each Borough licensing its own drivers, a ‘national’ tram driver’s licence was inappropriate. The reasons for this were that a driver trained on the equipment and routes for city A could not, without retraining, drive a tram in city B; in fact to attempt to do so would be positively dangerous despite the protestations of a self-appointed tram driving expert who sought to have his courses recognised as a suitable qualification for the issue of a ‘universal’ licence.
The approval process has evolved into a staged one, beginning with the necessary approvals of the infrastructure especially the traction power arrangements. Then follows a period of training on the actual tramway; if the system is fortunate to have a reasonable length of off-street running it enables everyone to become accustomed to handling the vehicle before launching onto the far more difficult task of driving amongst road traffic. During this time various operational procedures, particularly those dealing with accidents and emergencies need to be worked up. This does not only affect tramway staff. The Police and Fire Brigade also require training. An early decision has to be taken as to how and who applies earthing devices if traction power has to be discharged in an emergency. When all the necessary training has been done approval to begin trial operational running may be given. During this period of intense operations several exercises need to take place to examine the arrangements for handling emergencies; these should involve all the emergency services. This period of trial running should, in my view, last for at least 4 weeks providing there has been sufficient time for preliminary training of the individual parts. It would be unwise to plan for much less than 6 weeks to elapse between trial running beginning and any opening to passengers and a much longer gap should be allowed before having a grand opening ceremony. This may seem unnecessarily gloomy but comes as a result of bitter, but vicarious, experience of systems trying to run before they can walk.
In my next, and last article, I intend to look further at the place of the ‘operator’ in the development of a new scheme and to couple this with some comments on the past, present and future of modern tramways in the UK.
Making LRT systems safe Pt. 3: top of page