This blog has always been a great advocate of looking beyond the surface of any numerical claims. That's because they're hard to understand and interpret. But it's also because they're made up. In the best sense, of course, in that you've got to build them up from other numbers - with different meanings, provenances, orders and structures.
It's the same with all the claims and counter-claims about High Speed Rail 2 (above), which is supposed to take very rapid trains north of London, to Birmingham, Leeds and Manchester, in two stages over the next couple of decades.
It's probably - just about - still worth building. No doubt the Great Western to Bristol looked like a big gamble when Brunel laid it out. But it worked - and it still works, with essentially the same line carrying tens of thousands of people a day. The chance to build this kind of infrastructure comes along only once in a lifetime - and in HS2's case, perhaps once every several lifetimes. It will serve as a workhorse of British travel for many, many decades, meaning that the money spent might still be worth it. If its costs keep rising, it might one day be time to pull the plug. That moment doesn't seem to have arrived yet.
But the thing that we can say right now is that you should beware of the traps involved in taking all the claims about its economic benefits too seriously. These have been officially revised down now on so many occasions that it's not worth even putting up all the links. And why? Because the business case rests on lots of assumptions that you might or might not want to make. About how much the time of leisure and business passengers is worth, and the relative merits or demerits of upgrading other lines. About how much work business passengers will be able to do on wifi-enabled trains and on their smartphones. About growth in provincial cities, and indeed the economy as a whole. About the true costs of planning blight. About the mulitipliers to apply to the building work in the first place. And so on - and on. You can plug the data in and get pretty much to where you want to go - which helps to explain the confusion and the doubt around this project, and many others.
It's a pity, really, because it's these indeterminacies that allow the scepticism about everything and anything government tells us to continue growing - an increasingly powerful force in our politics that at first appears far from the apparently-prosaic realities of a train line. It doesn't help that the Government made such a comprehensive mess of the renewal of Virgin's train franchise, in a Yes Minister-style foul-up involving a junior civil servant typing the wrong values into an Excel spreadsheet. But the real challenge to our public policy is far deeper: how can we even discuss our collective choices when even the basis of the numbers are now so complex - and so contested?
There isn't a technical answer. There's only a philosophical and, at one and the same time, a practical one. It's called politics - the art of choice itself.
