Two studies on noise abatement in urban areas, performed for the Dutch Ministerie of Transport (SSZ program), are presented. The first is a feasibility study on noise reduction of a range of vehicles. Buses and lorries were found to have comparable noise levels, whereas delivery vans and taxis were found to be much quieter. Specific noise sources can be high. More stringent (European) regulation or governmental stimulation measures are required. A survey was held amongst 396 inhabitants in two cities. Most noise disturbance was shown to be caused by buses (low-frequency acceleration noise). The second study was on noise disturbance during goods delivery to shops. This was initiated after the extension of business hours and the introduction of stricter regulations (60 dB peak limit). Current measured peak A-weighted noise levels at 7.5 m were found to vary between 60 and 95 dB. The study concluded that noise control measures for most sources are technically achievable within three years. Initial estimates indicate 10%–20% higher investment on vehicles and handling equipment. Lorry diesel engine noise is about 15 dB too high. Well-designed quiet electric traction systems are a quieter alternative.

Experimental and theoretical investigations are presented of the performance of noise barriers in the open air. The experimental work includes full-scale measurements on barriers and scale-model measurements on a barrier in a wind tunnel. The wind tunnel experiments indicate that meteorology has large effects on barrier attenuation. The results of the wind tunnel experiments are compared with results of numerical computations with the parabolic equation method. Good agreement with the experimental data is obtained only if wind speed profiles as measured in the wind tunnel are used in the computations. It is concluded that wind speed gradients induced by the barrier itself reduce the barrier attenuation considerably: reductions as large as 10 dB are found. The use of aerodynamically optimized barriers is proposed in order to minimize this reduction of barrier attenuation.