Vehicle-induced air pollution and traffic noise on a local scale are determined by road traffic volume and the spatial distribution of traffic flows. The purpose of this report is to identify factors influencing this spatial distribution so as to improve the modelling of local traffic intensities at a national level. In this way, estimates of local traffic-induced environmental problems will be made more reliable in future environmental outlooks. Specifically, the study sought an answer to the following questions: (a) What factors determine the spatial distribution of passenger car traffic flows and freight traffic flows; (b) To what extent are these factors taken into account in the current prognosis models, for example the PION model (a Dutch prognosis model for developments in local traffic intensities); and (c) what are the recommendations for improving this model? The results of an analysis made in eight Dutch cities underline the importance of infrastructural and geographical factors, such as distinguishing between road types and the location of roads in relation to the city centre. A concentration of traffic flows on the main roads and a shifting of traffic intensities from the city centre to the outskirts were ascertained for 1987-1997. These observed trends are incorporated into the PION model. This improved PION model could be used as an initial step in improving the modelling of the spatial distribution of traffic flows. Recommendations for future improvements are the collection of data for more and smaller towns, and a more comprehensive inventory of the freight traffic distribution. (A)
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