GR Heath's letter (NCE last week) reads like post-rationalisation. Funding decisions on any major capital project are taken against a backdrop of conflicting political pressures. But other factors which are easily overlooked with hindsight include the 'drivers view' of the economic situation prior to the decision being taken.
It seems to me that any forecast of the economic environment or transport policy in the 1970s, however well informed, would have to have been seriously revised by the time of the start of the Channel Tunnel.
On a smaller timescale, each decision taken on such a large project can be overtaken in the interval between the decision date and the completion of the project.
Mr Heath suggests that the Jubilee Line Extension should have been commissioned as a standard gauge tunnel. Tunnel boring machines have indeed revolutionised underground railway construction. But the economics surely cannot be that simple. High rates of advance, though important, must be set against the square law cost of increased diameter, and other factors like alignment restrictions and existing assets.
The logic that it would make more sense to start reinventing the whole of the London Underground system, rather than continue the system for the sake of a relatively small extension, escapes me.
Mark Whitby is right; the population at large is not interested in the hard work needed to understand the reasoning behind public investment decisions. It prefers the armchair critics' prose, and the press likes to give the public what it wants.
Andrew J Allan (M) Allan Consulting. 3 Soden Road, Heyford Park, Oxfordshire OX6 3LR