Chapter 33: Unintended Effects of Polices

Most transport policies and substantial projects are implemented with an implied or explicit understanding of what they are intended to achieve – faster travel, or less congestion, or a reduction to environmental damage, fewer accidents, advantages for particular groups, economic regeneration, cost savings, etc. Confidence that the initiative will genuinely contribute to such objectives is usually sought through some sort of formal assessment or appraisal, using a model or set of calculations that estimate how big the effects will be. Such calculations are always simplified in some way or other – it is not remotely possible to calculate all the direct and indirect effects on individual choices and the whole economy, partly because we do not know them all, and partly because even if we did, it would be too big a task. And even those quantities that are calculated may not necessarily be correct, because of faulty assumptions or a biased modeling procedure. The hope is that the main effects will be approximately right, and the omitted effects will be unimportant.