There has been considerable interest, in recent years, in assessing the environmental effects of traffic. The purpose has been either to predict the impact of now roads and traffic management schemes or to identify those locations in most need of relief from undesirable traffic effects. It was thought important to know the actual levels of nuisance which particular traffic flows caused, the factors which caused nuisance and also the changes in people's opinions of nuisance when a change in the amount of traffic occurred. This interest was reflected in the attention the 'Advisory Committee on Trunk Road Assessment' paid to the assessment of environmental factors as an essential element in the appraisal of trunk road schemes. New roads may increasingly be built for environmental rattier than traffic benefits so it has become more important to assess the environmental impact.