A lot of this is getting quite off-topic now, but I feel I have to respond to some of these points.

Yes, it is. The current plans place a lot of emphasis on upgrading trunk roads managed by the Highways Agency to dual carriageway and grade separated junctions. If you're interested, there's a list of these projects on the Highways Agency web site.

And likewise that is why significant junction remodelling works are going on at some of the major black spots for this, such as the bottom of the M6.

But those are rarely heavily congested, nor likely to become so because as you say they are typically there to serve specific local requirements. It's really the main trunk roads that we need to consider if we're comparing the efficiency of road transport with the rail network and potential high speed rail infrastructure.

Perhaps, but any given driver is still driving no more than one of them at once. We're seeing more two-driver households that have two (or more) cars and as a general demographic trend more people are staying single for longer and many of them have their own cars. However, neither of these factors (but particularly the first one) necessarily means all of those extra cars are being driven all the time.

It's also worth noting that with the general hostility toward new/young drivers these days, particularly within the insurance industry, more people are waiting until well into their 20s to take their driving tests, which will reduce the number of (legal) drivers if the trend continues. At least for the next few years, it looks as though this effect is going to more than cancel out the increase in the general adult population that you mentioned. (This is actually one of the stronger arguments for improving public transport provision at the expense of funding improvements to the road network.)

That is true up to a point, but you are oversimplifying. Traffic engineering can be a surprisingly interesting field, because you get all kinds of perverse-seeming behaviours that actually make complete sense when you consider the actors with their local knowledge making decisions in isolation, but which result in tragedy of the commons kind of outcomes. We see this every time a motorway is congested, when the most efficient way to use the space is to have the traffic slowing down and moving uniformly, but there is always Lane Changing Guy who has to jump around cutting everyone up so he can get there five seconds sooner.

There are also all kinds of circumstances when the modelling these guys use still makes daft assumptions which predictably result in unintended outcomes when implemented. They just spent about half a million pounds "improving" a roundabout on the Cambridge ring road to make it more cycle-friendly, but because they apparently didn't understand the ideas they were borrowing from abroad and didn't implement the whole system, the only reason the roundabout has a lower risk of collisions involving cyclists now is that hardly any cyclists will use it any more. This anecdote is really off-topic now so I'll stop there, but it does illustrate the hazards of using a mathematical model that isn't sophisticated enough when you're predicting how roads will work.

I don't think it's a question of ignoring the indirect benefits. As I see it, since we can't know what true benefits will be derived without doing the entire project anyway, it is probably more fruitful to consider the likely benefits relative to other options. In particular, one other option is improving existing transport infrastructure instead of building a completely new long distance, high speed railway line.

We do know that HS2 could only transport a modest number of people compared to the overall railway network, even at its full long-term capacity. We also know that it will offer only a modest reduction in journey time, so almost certainly a quantitative but not qualitative improvement for most passengers. (This is one area where the high speed rail in the UK may differ from the high speed rail in Japan that started this whole discussion.) So whatever indirect benefits may result from creating HS2 are likely to be more incremental, evolutionary improvements in the affected local economies and communities, rather than dramatic shifts in productivity or quality of life. The flip side is that you could do a lot of that with the kind of money we're talking about if you invested it elsewhere in transport infrastructure, and a lot of those projects have much more predictable and reliable long term benefits than the relative unknown of high speed long distance rail.

We must be talking about different countries. Here in the UK, road infrastructure funding has fallen about 80% in real terms since its peak. Across the Channel, the French have built as much new road over the past couple of decades as we have in our entire road network.

Which, with due respect, is an awfully convenient method of hand-waving away the staggering costs and significant disruption of such a project while demonstrating neither any verifiable level of benefit nor any objective advantage relative to other work that could have been done instead.

To put this in perspective, the official estimates for HS2 costs are currently £42.6B for the line plus £7.5B for rolling stock, which is in the general region of £1,000 for each person in the working population. For comparison, the same amount of funding could build about 90 large hospitals like this one, or fund the government's entire national road network enhancements programme almost twice over, or fully fund a major government department like Education or Defence for a year, or pay the interest on the entire national debt for a year.

You need a lot of indirect benefit from a high speed rail project like HS2 to outweigh those kinds of things. I'm not saying it's completely impossible that such benefits will eventually result, but a bit of optimistic commentary doesn't go very far in making the case.

That must be a different continental Europe to the one I visit, then, because every time I go the old school trains seem to cost single figures of Euros for a whole day of travel, while taking a single Eurostar journey between major cities is typically two orders of magnitude more expensive. In some cases the latter also require booking in advance, unlike the older long-distance routes that have often been shut down once a Eurostar-style high speed replacement is available.

It is self-evident that if you build enough road then there will be enough space for a finite population of drivers and vehicles. It is also obvious that we physically have enough resources to do so. The road-building question is a cost/benefit trade-off, a matter of what is practical to build given realistic time and money constraints, opposition on environmental grounds, opposition from those who would be disrupted by the work, and so on.

I didn't respond to the point you made relating to junctions, because you claim without evidence that it's not possible to avoid them in most cases, yet the reality at least here in the UK is that many of the major road-building projects in recent years have been carried out precisely to simplify junctions or eliminate the need for some of them altogether, while others have been widening trunk roads that have insufficient capacity, which doesn't necessarily create any new junctions at all.

I'm not sure you understand the practical relationships between government and big business in Japan.

Also, speaking of basic fact checking, you might like to consider the origins of the commercial operation behind today's Shinkansen. Hint: The original developments were a financial disaster, and got snapped up for the equivalent of cents-on-a-dollar money at privatization after the government had invested a fortune in the early days.

But it is true that the situation in Japan is not directly comparable to other high speed rail such as European or US networks and their potential developments. The economics, demographics and geography are different, and do make very high speed rail a more attractive proposition in Japan.

I don't know enough about US infrastructure to know how much potential there might be in that idea, but sure, reasonable alternative strategies should always be properly considered.

For the kind of very high speed, maglev-based trains we were originally talking about, I wonder how much any advantage in somewhat faster movement would really be worth. Presumably the implications for increasing the spec on the infrastructure to cope with shifting much heavier trains would be significant, and you would need a lot of trains to shift the kind of volumes that modern container ships routinely carry, so I suspect when you looked at the facts and did the math the idea of fast transcontinental rail freight might be a non-starter.

Even so, the modern container-centric shipping industry is one of the most remarkable yet unspoken success stories of the technological world, so it surely makes sense to integrate general developments in rail infrastructure with shipping where there is an advantage to be had.

Maybe. There obviously are people in British politics today who genuinely want to make things better and have worthy principles to match. There seem to be at least a few in each of the major parties in our various national assemblies, and you'll find others if you look at those who are active within smaller communities and local government. What saddens me is that the system appears to be constructed so that only those who play the game and toe the line can progress to the top, and thus we find ourselves with political leadership who don't seem to have enough bones to form a spine between them. That particular systemic failing seems to be responsible for a great many ills in our societies today, not the least of which is a tendency to chase high-profile projects whether or not they are really the best way to proceed.

Right, but there are only going to be relatively small numbers of them as well. Once again, we're talking about enough money to instead make dramatic improvements to the existing rail network, or to upgrade national communications infrastructure to make teleconferences (and remote working more generally) much more practical, or numerous other things that would also benefit exactly the same kinds of people who might benefit from the existence of HS2.

It's also important to realise -- which many people don't -- that when these new high-speed lines are introduced, they often have a negative effect on some travellers. In a nutshell, prices are typically far higher to travel on the high speed trains, and there is a significant emphasis on booking as far in advance as possible because of limited capacity. However, once those services are available, the existing long-distance routes on existing network infrastructure tend to be scaled back, actually reducing the quantity and quality of the available alternatives. It remains to be seen whether saving an hour or two travelling between two big cities on a journey that is still going to take several hours is really that helpful when it happens at the expense of much higher ticket prices and a general reduction in flexibility in rail travel as a whole; evidence from what has happened so far in places like Europe and Asia is not exactly a glowing endorsement of this strategy.

Of course it can. You might not like the financial or environmental implications of taking that policy to its logical conclusion. (Neither would I, for the record.) However, there are only so many people in this country, only so many cars for those who drive to use, and only so many hours in the day for them to spend behind the wheel. That creates a hard upper bound for the capacity required, even before you apply common sense and make more realistic assumptions about how long people will actually be willing to spend driving even on a perfectly efficient road network.

I know it's a popular sound-bite, particularly for the green movement, to claim that you can't build your way out of congestion, but such a general and unqualified proposition doesn't stand up to even elementary scrutiny. There is no question that we could do exactly that, but the interesting questions are all about whether or when we would want to.

I'm certainly not against investment in rail in general. I believe the most effective and efficient transport system must be a combination of mass and personal transit, playing to the strengths of each where you can/must.

All I'm saying in this thread is that there are genuine concerns about whether high-speed rail of the kind we're talking about in Japan or less extreme versions like HS2 are justifiable given how much they cost in various ways and how few people they directly benefit.

That is true, but there is a much higher chance that you will benefit indirectly from improved transport infrastructure that helps anything you buy get moved to your local area so you can buy it. HS2 isn't, as far as I know, currently expected to carry much if any freight itself, and arguments that it will free up significant room on the existing railway network for freight by shifting long-distance services have been criticised for various reasons.

That is certainly true as a local effect and up to a certain level, and it is therefore something that should be taken into consideration when planning whether and where to improve the road network.

In that case there really is a reductio ad absurdum case, though. Suppose you can open up an often overcrowded route such as the M25 enough that all traffic can move twice as fast at busy times. You save a lot of time for a lot of people, and of course you also improve the environmental situation (at least, if you ignore the costs of the development itself and look only at ongoing fuel consumption and emissions by vehicles using the road). Would this mean some people would commute further to work or relocate? Sure. Would it mean everyone using the road would extend their commute or relocate their business to cheaper areas outside London and therefore just shift the burden elsewhere? Of course not. People drive to places for specific reasons, and they choose those places for other specific reasons, and neither those reasons nor economic drivers would completely or even mostly negate the benefits if we could move to some hypothetical road transport network that ran with 100% efficiency tomorrow.

I know people who were seriously hurt in the London transport attacks, so while I'm not That Guy who thinks everyone who writes something dumb on the Internet is actually a terrorist, I still find such "jokes" in poor taste. Your mileage may vary depending on how many people you know were permanently disfigured or disabled just because they took the wrong train one day.

Also, if you read my previous post properly you'll find my figures are right about 9/11. Not that it's really the point; I don't meet a lot of people who think jokes about flying planes into buildings are funny and I don't imagine I'd meet many more if each plane crash that day had only killed a hundred innocent people instead.

Yes. I'm in Cambridge, and Julian Huppert is currently our MP.

I'm not sure for how much longer that will be true, because he's a Lib Dem in a seat that can swing sharply from one election to the next, and I suspect the Lib Dems are in real danger of being annihilated at the next general election thanks to some poor leadership decisions in recent years.

Personally, I'll be sorry if he does go. We don't always agree on policy, but at least he's the kind of representative someone can have an intelligent discussion with and if he does still go another way then he's probably got a reasonable basis for his position. I think we need more people like that in government whatever colour is on their party flag (and fewer people who think the appropriate response to intelligent discourse in government is mockery).

Right, so if the long term goal is to run these trains at close to 900kph, and something has gone wrong badly enough that they crash in the first place given the design, it's going to be some sort of catastrophic failure.