I was taught rolling related wear varied with 4th power of static axle load which is a bit more than an exponential increase...
On roads an HGV causes 6,000 times more wear than a small car.
So how does that work out in the case of the IEP v loco-haulage? A class 220 vehicle weighs about 44 tons compared to a trailer at about 35 tons and a loco at around 80 tons. There is going to be a break-even point somewhere. Can you work out where it is?
In an actual situation, all other things are not equal, as wear and tear will depend on other factors such as the compliance of the suspension.
Do you have any examples that confirm this fourth-power effect in practice, where tracks are used by trains with much heavier axle loads than used in the UK? They must suffer extraordinary rates of wear. Do they?
Since you have studied this subject, what is the effect of wheel radius on track wear?
26 metre trailers, the standard length in mainland Europe, seem to weigh, typically, about 45 tons, incidentally, so if axle load was such an issue surely the IEP should have stuck with 23 metre vehicles. There was also the compromise option of having another two-loco train like the HST, or an over-powered EMU with trailers which were drawn off and used on the non-electrified section of the route by a loco of lower power, as happened on the Waterloo-Bournemough-Weymouth route after 1967. Or a six-axle locomotive.
Whichever way this is looked at, it seems as if there were many other viable, and probably less-costly, options than the IEP solution. The latter was in any event very different from what was originally specified, which no manufacturer could deliver. That says a lot about the concept.
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6400 extra seats in the high peak hour, although it is only possible for a short period of time as the line is bi-directional and then has to close to inbound traffic to allow the trains to get back out of Waterloo in the morning (and the revers in the evening). Meaning that rather than being able to run 1tph to each of the key desitinations (as there about 12 if you include the various loop lines, suburban services to Woking and Guildford, etc.) it is in reality only really 0.5tph.
However it is also likely that such an intensive use of the line owuld only be seen during the peak hours so as to allow the stem a little more space for when something goes wrong to be able to get back on track (as has been proved as of late).
IEP would allow the GWML to achive about 20% of that without any extra works and the GWML is unlikely (even with the removale of trains at Paddington due to Crossrail) to be able to achive such an increase due to Paddington having fewer platforms.
In reality the 5th line for the SWML is a stop gap until Crossrail 2 is built, which would see a step change in the number of services for all desintations.
It should also be noted that the SWML has already seen lots of services see more seat crammed in (one fo the points that is trying to be avoided by those adicating alternitives to IEP's), for instance, post the 5th line I doubt Portsmouth will see the 450's replaced by 444's during the peak hours. As without outher infrestructure improvements (i.e. further spending) many key desitinations on the SWML are unlikely to see extra trains.
I do not doubt your calculations but a 10 car IEP would provide the same number of seats as the 9 car ones actually ordered, but with a decent amount of space for everyone and their luggage, and pro-rata for the shorter units.
That is what the criticism is ultimately about for the end-user's point of view.
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The problem is in 10 years of 2.5% growth there is 28% growth, whilst IIRC IEP will provide 18% more seating than the HST's, meaning that 10 coach trains could be required before HS2. Even post HS2 pasenger numbers on the WCML, ECML and MML will fall to about the numbers seen in 2000, which means that the trains are hardly going to be empty.
Also, short of an extra track (or two) along the length of the GWML (or at least most of it) there is little else which could be done to improve capacity. However as pointed out before infrestructure is very expensive compared with new trains.
Given the 5th line on the SWML near Waterloo is costed at £1bn and will not improve things by very much or over a very long length even if alternitive trains which were half the cost were purchased there wouldn't be much budget to do very much at all.
This is an interesting analysis but surely the main area of congestion on GWML is between Paddington and Heathrow Junction? And surely the logical solution to that is to get the Heathrow trains off the GWML altogether?
Beyond Heathrow the present suburban trains will be replaced by Crossrail, which takes pressure off the approaches to Paddington. Beyond Reading, towards Newbury and Oxford, the suburban trains are still only, at most, 2 x class 165/166, so there is still spare capacity there. Oxford will soon get a new route to London Marylebone, again, further adding to capacity. Didcot to Swindon used to be four track and that would cost no great fortune in land acquisition to get the tracks back in place. That is a lot of potential extra capacity.
Only when all that potential capacity has been taken up are we are at the point you describe where additional infrastructure would be needed, at great cost. In the meantime, IEPs with one extra vehicle would give passengers and their luggage a decent amount of space for many years to come, probably much of the design life of the trains.
The capacity problem itself is partly a consequence of the absence of an effective national land-use planning policy. As a result, people are crammed into the bottom right-hand corner of the country. There are reasons for that which are outside the scope of Railway Forums, but failure to address them is putting undue loads on the infrastructure. It is not just the railways that are given the headache of having to deal with the effects.
