Edwin_m

You'd still need a mechanical backup in case the power failed or to apply/release the brakes when not coupled to the loco.

Nothing like that on a tramway, which basically follows highway practice. Crossings on segregated tramways normally just have passive measures, although a red/green man or the obsolete arrangement of orange flashing lights may be provided at particularly risky sites. Having said that there have been quite a few serious incidents where trams have struck pedestrians on crossings and the designers are now much more aware of the issues.

The Value of Preventing a Fataility was around £1.5m at the time of TPWS, based on surveys asking how much of their own money people would be willing to spend to save the life of someone who was not a close relative. It's actually much lower now, I think because there is a common figure between rail and highway which there wasn't at the time. Even at the higher figure TPWS was a bit marginal, and I think some of the extra features added during development probably pushed it over.

A lower speed would not reduce the cost much. The minimum radius would be less but the designers have already had to reduce the speed where it isn't possible to accommodate a 400km/h alignment without unacceptable disbenefit. The fact they have done this in some places suggests they would have done it elsewhere as well if there was a reason to do so. The fact it's mostly designed for 400km/h doesn't mean it will be used at that speed - the published journey times are based on a maximum of 330km/h. The top speed will be chosen nearer to the opening date in the light of train technology, energy costs and the state of competing modes at the time. As I said above there is very little extra cost incurred if the present route ends up being used at a lower speed, but a huge amount extra if a lower design speed was assumed now and conditions closer to opening date suggested that 400km/h was more appropriate.

The GW ATP system was introduced before Southall and Ladbroke Grove. It was isolated on the train at Southall because (IIRC) the driver wasn't trained it its use, AWS was isolated due to a fault so the driver had nothing to alert him to adverse signals. Only Great Western trains were fitted with ATP on that route, so the SPAD by a Thames Trains unit at Ladbroke Grove was not protected. GW ATP is still in use but the decision was made not to adopt either this or the Chiltern system on a wider basis (though it was extended to Heathrow and the Heathrow Express units when that route opened). TPWS was thought up as a system that would address the majority of the ATP-preventable risk but would be much cheaper, easier and quicker to fit. Authorisation was awaiting sign-off by John Prescott's department at the time of Ladbroke Grove. Although the Uff-Cullen report was rather sniffy about it, subsequent experience has borne out the TPWS casualty reduction predictions (which I had a small part in making).

Highway engineers of my acquaintance use "in advance" to mean the opposite of the railway meaning. In my view the frequent transfer of labour between railway and highway contracts makes that one difficult to defend these days.

Well someone has to pay it and if the damage from heavy goods vehicles is indeed so great then it would be a good idea to reduce it. For example would "hub and spoke" be the preferred distribution model if the haulier had to pay a lot more for their mileage? Or should we be going over to concrete pavement?

That has been worked out in the HS2 documentation but I haven't time to look it out now. The junction for any Heathrow branch/loop would be well south of the Chilterns - somewhere near Ruislip I think - so any Chilterns station would be on the main line. Again the Heathrow junction is discussed somewhere in the HS2 documentation.

If road hauliers paid something like their full infrastructure costs then they would be more incentivised to minimise damage to the infrastructure. This might lead to different ways of working, such as use of more sophisticated vehicles that cost more but damage less (as has happend on the railways with track-friendly bogies). At worst the total cost to the national economy would remain the same (the roads still cost the same to maintain but this cost would be paid by users of goods transported by road, instead of being paid by taxpayers - who are largely the same people). If the incentivisation works then the total cost would fall.

You said "airport branch" not "Heathrow branch" so I misinterpreted that. A station in the Chilterns would cost two paths for each train that stops there, unless its stopping service was frequent enough that the path vacated by one stopping train was filled by the previous one accelerating away from the stop. I think we've been though that issue at least once already on this thread. The original HS2 reports made a very good point that no one station would serve all of Heathrow, so if airport passengers have to make a transfer to get to their terminal they might as well make it at Old Oak Common. Changing there would also give a better choice of train and destination on HS2, as there are only two Heathrow trains per hour in the proposed HS2 service pattern. And the Heathrow people don't seem to accept that HS2 avoids the need for the third runway, as they are still putting the runway forward in the full knowledge that HS2 is proposed.

Unfortunately HS2 wouldn't have capacity to act as the link between London and its principal airport, unless - possibly - the airport station was on the main line and could be served by trains going on to other destinations. Heathrow doesn't have this problem as there are other services to provide the link into central London. This limits the airport site considerably, and I think I've already posted about the small likelihood of a site alongside the HS2 route being locally acceptable. If you think high speed rail is causing a rumpus along the route, just see what happens if you propose an airport there as well...

I doubt it will be MMA doing anything. The combination of reinstatement costs, legal action, increased insurance premiums and loss of reputation means they will almost certainly disappear from the scene. Given that they've tried and failed to run the trackage at minimum cost I would have thought it was quite likely to be abandoned, and many other marginal short lines could go the same way.

Anyone who is intending to take legal action will want to be doing all they can to pin on the company rather than the employee, for the simple reason that the company (or more correctly its insurers) has more money.

They stopped running routinely in around 1990 and new unbraked wagons were being built up until about 1960 - no doubt somebody can give better dates. Something that should have happened much sooner in my view, and where North America and practically everywhere else was well ahead of the UK. There were many serious accidents with unbraked wagons over the years, and others involving other trains being derailed by the sprung catch points that had to be installed on main line gradients to derail any portion of an unfitted freight that split and rolled back before it could do more serious damage.

Those are useful updates Gerald but I think Chris is somewhere in the right ball park. If the wagons were overloaded this would increase the train weight but also by the same proportion the restraining force exerted by any wagon handbrakes that were applied, but it would slightly increase the likelihood of the train rolling away because the loco handbrakes (if applied) would still be the same. The question of damage to the loco (or indeed wagon) brakes on the journey downhill is not relevant to whether the brakes were sufficient to hold the train where it was stabled, although it would have some effect afterwards and influence where the locos ended up. This depends on the answer to my question of whether the wheels slid or rotated against the brakes, since one would result in wheelflats and false flanges, and the other in brake blocks wearing and becoming less effective. The first would be obvious to investigators, the second perhaps less so. On reflection I think the wheels would still rotate, in which case the effective coefficient of friction might be less than 10%. It is possible the fire damaged the handbrake on the loco concerned, but we don't know anything about this. Indeed I don't think the use or otherwise of loco handbrakes in this incident has been mentioned in any of the linked articles.

Going by these figures the total weight of the train is 9669+500, 10100 tons to make the maths a bit easier. The force needed to hold a train on a gradient is given by the weight of the train multiplied by the gradient as a fraction, or divided by the gradient as a "1 in". For an 10600 ton train on a 1% gradient this is 101 tons. If the coefficient of friction between wheel and rail is 10% this force could be provided by 1010 tons of the train being braked, assuming the brakes are applied hard enough for the coefficient of friction to be the limiting factor (ie wheels slide along the rails rather than turning against the brake blocks). This back-of-an-envelope calculation suggests that 11 wagon handbrakes on their own would be sufficient but probably not allow enough margin for safety. Applying the loco handbrakes as well would give nearly a factor of two safety margin. Anyone please say so if you think I am missing something in this calculation!

This has already been covered. The brakes are failsafe in the sense that they will stop the train if the pipe is vented, but the brakes are held applied by air from the reservoirs and if no air supply is available these will leak off after a period of usually hours.

Just to be clear, if the air brake was applied on the train, then there would have been no pressure in the train air pipe. So, regardless of whether the loco compressor was running, the train brakes would have leaked off over time. The only brake that is affected by the engine shut-down is the air brake on the loco itself, and possibly the air brake on the coupled locos if these were also linked by a second (reservoir) pipe (I think it is US/Canadian practice to do this). However, given that the consist of locos is able to start the train on the steepest gradient, the air brakes on the same locos on would usually be enough on their own to hold the train on the same incline. Certainly if insufficient wagon handbrakes were applied the leaking off of loco air brakes could well make the difference between the train staying in place and rolling away. What happens with loco parking brakes? Do these apply on all wheels like the loco air brake? If so these could possibly also have held the whole train. An air brake in good condition will stay applied for several hour before leaking off, and days is not impossible. However if the equipment is in less good condition it could leak off within an hour or so, which I think is the sort of time after which the train must be secured by other means. Given what we hear about this operation I'd say it was quite likely that the leaking-off time would be close to the minimum.

The HS2 design is in fact at a very early stage. Phase 1 is being worked up to a level sufficient to support a Hybrid Bill but even if all powers and funding were in place there would be several more years of design work before it would be "shovel ready". As such it is entirely appropriate that a large amount of contingency is declared and the surprise is more that it wasn't included in the original figures. Remember how Crossrail found about £2bn of savings on a £16bn programme at the time of the 2010 spending review? Some of this was from re-planning the programme to adopt a cheaper construction sequence at the cost of a delay to opening, but I suspect a lot was the release of contingency no longer required as the design got more detailed. That was a drop of around 10% of the project value for a project which was at the time about two years past the stage of getting powers, and some seven years away from opening.

Thanks Mike - the Pan Am rulebook linked from here a couple of pages back required a procedure very similar to your first alternative.

I would think not only is it unseemly but also unwise. By saying this he would appear to have admitted legal liability on behalf of the company, since the employee was an agent of the company and if he indeed failed to apply the handbrakes (I'm not speculating on whether that is so) there are highly likely to be underlying causes for which others in the company are responsible. For example was enough time allowed and was the training up to scratch? At the same time he is throwing away any remaining shred of good reputation that the company might have retained if he had stood up and taken it on the chin.

I agree but only up to a point. This accident will probably skew the statistics to the extent that the railways of North America will have more fatalities this year than the railways of Europe, despite the latter having much higher density of people and trains and a lot more passengers. That doesn't happen every year, though I've just Googled a statistic that around 700 people per year die at grade crossings in the States. Putting these figures together does perhaps suggest that the risks inherent in running large trains (often of hazardous materials) through difficult terrain warrant the same level of safety procedures, equipment and culture as running fast and frequent passenger operations.

The very useful rule book link posted by highpeak confirms that railroads are fully aware of the risk of air brakes leaking off and therefore enough handbrakes must be applied to keep the train from running away. If a similar procedure was in force on the road in question then the question of why the engine shut down and the air brakes leaked off is no more than secondary - the train should have been secured by handbrakes whatever the air brakes were doing. On that basis the conclusion has got to be that either the procedure wasn't followed, with too few or no handbrakes being applied, or that the handbrakes were somehow interfered with after the crew had left.

The brakes are failsafe in the sense that they will come on if the pipe is vented, and hold the train for at least an hour. However if there is no source of compressed air the system will leak off and become ineffective, so if a train is left unattended some other sort of brake must be used.

How long does it take to pressurise all the reservoirs on a long train? I wonder if the reason to leave the engine running was just to avoid having to do this in the morning, but in my view it still doesn't remove the need to apply enough other brakes.