Sir – As Ian East will know (Letters, December 4) generated traffic does not mean that road expansion will not provide any benefit, it simply means it should be taken into account when forecasting usage.

In the case of the A34, an additional lane will make a critical difference to road safety by allowing cars to avoid being trapped in two lanes by heavy lorries and introducing a hard shoulder for emergency use.

This would be a much more robust highway, far less susceptible to random sudden stoppages.

The A34 was designated as freight route by the Government to connect Southampton docks with the north of the country when the A34 was extended to meet the M40. This will not change and probably does not hide much latent demand, as the trucks have few alternatives.

There will be some additional traffic created by a better road, but this will in part be traffic removed from rat-running through villages and in part a sign of increased commercial and social activity. All these would be direct benefits to local residents.

The trope that anything free at the point of delivery creates unlimited demand bears little relation to reality, when experience shows that the large number of transaction costs, psychological attitudes, social issues and opportunity costs combine to inhibit demand.

To give just one example, if empty roads alone were sufficient to create massive demand there would be no lack of traffic at night.

Gerald Dorey, Oxford