Since the beginning of the 1990's roundabouts have been increasingly constructed instead of signal-lamp controlled and priority controlled intersections of main roads outside and inside of built-up areas. One main reason is the improvement of the traffic quality especially in the minor streams because of the less waiting times, the other advantage is the decrease of the road accidents due to the traffic calming. The fulfilment of environmental impact assessment during the planning process of roundabouts is difficult because of lack of needed unified method and basic data. This report presents the results of air quality measurements before and after conversion to roundabouts in case of two intersections one in rural and one in urban area. On the basis of real life speed records the effect of the conversion on the specific emissions was evaluated in case of petrol fuelled passenger cars without and with catalyst as well as in case of a diesel fuelled car. Based on real noise measurements additionally the influence of the conversion on the noise level in the surroundings was evaluated too. The results of the "before" and "after" measurements and simulation tests showed that the conversion to roundabouts improves the local air quality and noise level up to certain traffic volume. (A)
Abstract