From Mr Stephen Plowden Sir: You report today ("Road plans thrown into jeopardy", 20 December) that the Department of Transport is to formulate new criteria for appraising road schemes which will take account of their traffic-generating effects. But the neglect of traffic generation is not the only, and perhaps not the most serious, defect of the present methods of appraisal. Of at least equal importance are the national traffic forecasts, which provide the input to the whole evaluation procedure, and the failure to compare road building with any other measures.

In May 1989, the Department of Transport took advantage of the very rapid growth of traffic produced by the Lawson boom - a growth that has not been sustained - to revise its long-term traffic forecasts upwards. Later that year, Chris Patten, then Secre t ary of State for the Environment, described the new forecasts as unacceptable. They are, in fact, physically impossible: neither the roads currently planned, nor any other feasible road-building programme, would provide enough capacity for them to be rea lised.

In towns, the alternatives to road building include a whole range of traffic restraint and calming measures, as well as better provision for pedestrians, cyclists and buses. Such policies in towns would have some dampening effect on traffic growth outside; they should be supplemented by lower and better-enforced speed limits, the abolition of tax concessions on company cars, the restriction of heavy lorries to a limited network of motorways and other selected roads, higher fuel prices (which are alreadycoming about) and perhaps some form of road pricing, especially for lorries.

The impact that these reforms would have on the level of traffic and its rate of growth cannot be predicted precisely, but it would be major. The only sensible course is to implement the reforms and to observe their effects, and in the meantime to imposea moratorium on all road building designed to increase capacity. Some bypasses can be justified by the relief that they would bring, even given present or reduced levels of traffic. The moratorium would not apply to them, but even bypasses should not bebuilt unless there are no other means of bringing relief, and unless they are accompanied by traffic restraint within the bypassed towns, to ensure that the relief is permanent.

Yours faithfully, STEPHEN PLOWDEN London, NW1

20 December