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When you consider Magnetic Levitation as a serious form of ground transport, traditional safety issues emerge
We too easily take for granted the checks and balances which ensure safe operation of the railway and, when things go wrong, seek to protect passengers and train crew from the consequences. Newcomers to the industry often regard this structure as archaic, arcane or irrelevant. But it matters not whether you run on steel wheels, magnetic flux or air cushions, similar principles apply.
These thoughts are, of course, raised by the accident on the Transrapid test track in Germany on 22 September when, according to reports, the Maglev vehicle travelling at 120mile/h hit a maintenance vehicle on the track. It was a particularly sickening accident because the news reports were the opposite of what you expect for a railway.
In many cases, the early reports of a high energy train collision start with inflated estimates of likely fatalities. The toll then falls as the rescue teams get into the wreckage. Colwich, 20 years ago this year, is the classic example.
But with the Maglev accident it just got worse. The late night news put the dead at 21. When something woke me in the middle of the night and I turned on the radio, it was up to 23 out of 29.
|
End section |
Middle section |
Length |
26.99 m |
24.77 m |
Width |
3.70 m |
3.70 m |
Height |
4.16 m |
4.16 m |
Empty weight |
48.0 t |
47.0 t |
Payload capacity |
14.0 t |
17.5 t |
Passenger Capacity (seated and standing) |
108 |
128 |
Total weight |
62.0 t |
64.5 t |
Source: Transrapid
Transrapid talks about ‘vehicles', which are made up of ‘sections'. The vehicle in the collision had three sections. Table 1 gives the basic parameters.
Running on rubber tyres along the top of the guideway, the maintenance vehicle weighed about 50 tonnes – in other words TRAMM or MPV sized in UK railway terms. Like these vehicles it has an underframe with a separate superstructure, plus a platform at one end to carry equipment.
It seems to have been hit from the platform end. Some of the superstructure was destroyed, but, from photographs, the underframe appears to have remained intact.
I make the kinetic energy of the three section vehicle at 120mile/h around 200MJ. At the moment of impact, it would have had to accelerate the maintenance vehicle up to speed.
Simple Newtonian mechanics suggests that this involved the transfer of around 50MJ of energy. For comparison, UK ‘crashworthiness' requirements specify that a cab end should absorb 3MJ for trains running at over 100mile/h.
During this energy transfer process the front of the Transrapid was subjected to unimaginable forces it was never designed to resist. The maintenance vehicle ended up embedded in the vehicle.
Aerial views show that the damage extended back about half-way into the leading section. In other words, it took the destruction of about 13 metres of the vehicle structure to absorb the energy transfer involved.
Again, for comparison, at Ladbroke Grove, the driver of the Thames Turbo died with 19 of the 25 passengers in the leading vehicle. But this had borne the brunt of a head on collision with an IC125 in an accident where over 400 Mega Joules (MJ) of energy had to be dissipated.
There are a number of contributory factors to be considered. First, since Transrapid runs on an elevated guideway its designers assumed that a vehicle would never hit anything and so ‘crashworthiness' and structural integrity were not a design requirement. Most of the weight goes into the magnets, batteries and other equipment. The vehicle structure is built to aircraft standards.
Secondly, as Table 1 shows, each section is similar in length and weight to one of the new generation of heavyweight 125mil/h diesel multiple units. If a Voyager hit a TRAMM or MPV at speed you would not expect half the leading vehicle to be destroyed.
Apart from the, largely irrelevant, cab-end ‘crashworthiness', the body structure of modern rail vehicles are designed to take specified static end loadings of around 300 tonnes in old money. This column has frequently lauded n the proven structural integrity of the 35 year old Mk 3 coach design.
But in surviving the highest energy collisions, the ability of a rail vehicle to move in three dimensions after a collision can be significant. This may seem counter-intuitive, but, as at Colwich, coaches jack-knifing or sliding sideways help dissipate energy which would otherwise have to be absorbed by the vehicle structure.
In contrast, a Maglev vehicle cannot derail and all the collision forces are taken end-on. Structural strength is thus more important when you cannot derail. Readers may care to challenge this view.
All this leads to the conclusion that, were a high speed Maglev system to be built in Britain, collision resistance would be a significant issue, despite the dedicated, elevated guideway. Note that the new safety regulations associated with Interoperability are known as ROGS – Railways and Other Guided Transport Systems. And, yes, the ‘T' really is silent.
ROGS would also be concerned about emergency evacuation. All the reports of the accident referred to the difficulties rescuers had in reaching the Transrapid 15-16 feet above the ground. Ladders, mobile platforms and cranes were used.
Now assume a technical problem in the middle of nowhere on a UK high speed line. The Transrapid sits down. How do you evacuate the passengers?
One answer would be aircraft type inflatable emergency slides at each door. But would this be acceptable to the safety authorities?
It is worth remembering that when the first commercial Maglev system was installed linking Birmingham International with the airport, HMRI insisted on a full length walkway. Similarly, evacuation issues with the elevated monorail at the Midlands shopping centre were debated for months before it could enter service.
A valuable feature of Transrapid is that there is no power supply, as such, to the vehicles. The lift magnets are powered by batteries which are charged by power generated by a contactless system using the motion of the vehicle.
If power to the linear motor is lost, the vehicle still levitates and can ‘coast' under its own momentum. The theory goes that this would allow a vehicle to reach either the next station or evacuation point. While the linear motor would not be available to brake the train, separate eddy current brakes are fitted.
I don't buy this. If a high speed Maglev line is to pay its way, it is going to have to run vehicles at close headways to get the passenger volume. Since control is exercised through the drive, how would you maintain safe separation with multiple vehicles coasting down from 500km/h?
‘Lock, block and brake' may date back to 1889, but the principles are relevant to any form of tracked ground transport, of which railways are simply the oldest established. While Transrapid promoters Ultraspeed claim that the system has a European safety case, it is ROTS that would have to be satisfied.
H
A car on the platform hits a moving train – isn't that a precursor?
There was a diverting sight for early morning commuters at Royston on the morning of 19 September. Just as the 06.28 to London was departing, a car rolled out of the car park and came to rest with the bonnet bouncing along most of the length of the train. When the train had cleared the platform, station staff enlisted the help of waiting passengers to push the car back into the car park.
This is how the incident was reported in the log.
‘At 0653 station staff at Royston station reported that a car had driven from the car park onto the platform and had struck 2C70, EG, 0628 Cambridge – London King's Cross. The train had gone forward and was examined at Baldock with no damage found. The car was removed from the platform by staff. BT Police, were advised. The line was blocked from 0703 until 0707'.
Even with this column's robust approach to railway safety, this seemed a fairly hairy incident, so I asked Her Majesty's Railway Inspectorate and DfT's Rail Accident Investigation Branch what they were doing about it? And the answers surprised me.
HMRI said that its District Inspector was aware of the circumstances, but there would be no further action by HMRI. RAIB was more forthcoming.
A spokesman told me, ‘ RAIB isn't investigating this incident at Royston, although it was reported to them at the time. They decided not to investigate because there were no casualties or serious outcome - the train was able to continue its journey. They also decided that the time it would take to investigate and conclude would not be beneficial to railway safety overall'. He added, ‘If a station car park slopes towards the railway, then the site should be assessed for the possibility of this happening and a suitable set of reasonably practicable precautions should be taken'.
Now given the on-going problem with cars leaving the road and ending up on the tracks, most recently south of York , six days after the Royston incident, you might think that where the railway controls the adjacent infrastructure there would be concern if cars could still get onto the tracks. And, because accidents are so few, the Rail Safety & Standards Board, takes what it calls ‘precursors' very seriously indeed.
A precursor is an accident which might have happened but didn't. And the Royston incident seems a pretty obvious precursor. Suppose the handbrake released of its own volition, as happens, then later in the day the car could have rolled in front of a non-stop Cambridge-London travelling at speed.
It's not as if wheeled objects rolling off platforms is a novel threat. According to L T C Rolt in ‘Red for danger', at Wellingborough station on 2 September 2, 1898 a luggage trolley, momentarily left standing in a passage at right angles to the track, ran away across the platform and fell on the line where it was hit by a passenger train.
In the collision, the bogie of the 4-4-0 locomotive derailed. The locomotive ran on until it came to a diamond in the track, when complete derailment took place, causing seven fatalities.
An informed source seemed to remember that this resulted in a requirement for platforms to slope upwards to the platform edge. But when I checked with the fount of all safety wisdom Stan Hall, he found that the 1950 issue of "Requirements for Passengers Lines....of the MoT in regard to Railway Construction and Operation" made no mention of platforms having to slope away from the track and he had never come across any such requirement.
Of course Stan is nothing if not thorough and he then found that Clause 24(1) in the "Railway Safety Principles and Guidance, Part 2, Stations" ( HSE /HMRI) 1996 says that "All platforms should slope away from the adjacent track..." However, no guidance is given on the slope of the gradient slope.
While the Requirements and Principles are not applied retrospectively, they do show than someone remembered 2 September 1898 and sought to prevent wheeled vehicles running onto the track. So why are HMRI and RAIB so relaxed about Royston in 2006?