Re your article on Sustainable Mobility in January’s Traffic Technology International, one thing strikes me about road charging. Normally, if there is true demand for something, cutting it off causes real hardship (think of cutting off water, food, air or land) and if you substitute something else then you would expect there to be demand for that something. But if you cut off the supply of travel then for the most part it just stops, or at worst carries on regardless without knowing why (Jeremy Paxman never got a straight answer to his question what is ‘essential’ travel in the present snowscape), and there is no obvious demand for the cash that road charging would generate. This suggests there is no true demand for travel, only supply, or put another way ALL traffic is induced. As you say, road construction (and maybe improvement too) just increases speed, which is then soaked up by increased travel distances and longer-term adjustments to lifestyle and destination choice. One effect of this, apart from pressure on infrastructure, is to put pressure on other modes. If you depend on public transport, walking and to a lesser extent cycling, you will know that the one thing you need more of is time, whose value (under a fixed time 'budget') has been relentlessly inflated by motorists simply pressing a pedal. The absolute effect of congestion charging or fuel price on traffic levels is marginal, because the elasticity of car travel against cost is so low. But unlike running costs, charges reflecting ‘marginal social cost’ rise increasingly steeply with traffic, so effectively setting a ceiling on travel. If applied globally, this should lead to the apparent paradox of a reduction in fuel price, as the more costly sources of petroleum would be taken out of production. This would benefit truly ‘essential’ uses, if any can be said to exist, and it would also tend to decouple economic activity from fuel price, allowing it to be determined by less volatile factors, such as the carrying capacity of the environment. Finally, a morsel for thought. There has been much publicity recently about the ‘crash’ in demand for cars. While admittedly much of this may result from temporarily putting off purchases, it is further evidence of the discretionary nature of travel. It is no coincidence that creating car industries, and making and driving cars, is the most efficient way, in the ‘ecological’ sense, of consuming the supply of petroleum. Perhaps it is also no coincidence that car manufacturers take the prime slots in advertising, and promote largely on features which have nothing to do with function.