Further study of the composition of the Dutch car fleet

Abstract This article discusses the results of an investigation into the composition of the Dutch car fleet with regard to salient vehicle characteristics such as fuel type, unladen weight and age. Data for this study were collected by recording the registration numbers of cars passing six motorway locations at three distinct times of the day. Analyses of the results have revealed significant differences in the composition of these traffic flows with respect to both place and time. It is therefore recommended that account be taken of such differences when interpreting the results of noise emission measurements and measurements of air-borne pollutants and soil contaminants emitted by passing vehicles. It has been shown, for instance, that variations in the composition of traffic flows with respect to the unladen weight of the constituent vehicles could give rise to differences in noise emissions of up to 0.8 dB(A) for the average individual car between locations and times of the day. However, it should be noted that the unladen weight of a vehicle is only one of a number of characteristics that can affect noise levels. Speed, fuel type, engine size, tyre tread and the age of vehicles are all known to influence the level of noise generated when a car travels on the road. It therefore seems reasonable to assume that any differences in the composition of traffic flows with respect to these parameters will produce even larger variations in in-situ noise emission levels than are quoted in this paper.