Traffic calming has been shown to be valuable in modifying the speeds at which drivers choose to travel, and thus reducing levels of road accidents. However, there has been some concern that the gains might have been at the expense of the increased traffic noise and other environmental impacts. The Driver Information and Traffic Management Division (DITM) of the Department of Transport commissioned the Transport Research Laboratory (TRL) to carry out studies of vehicle and traffic noise alongside road humps, to measure the effects. The research shows that after the installation of road humps and speed cushions, the maximum noise levels from light vehicles (cars) are reduced. So too is the overall traffic noise level when light vehicles form most of the traffic stream. However, the effect of road humps and speed cushions on noise from large vehicle is more complex. Whilst there are some decreases in maximum vehicle noise levels from large commercial vehicles due to reductions in their speeds, this can be offset by increases in noise from the bodywork of such vehicles as they pass over the humps and cushions. The net effect of these vertical deflection measures on overall traffic noise depends on the proportion of large commercial vehicles in the traffic stream, and on the type of road hump installed. The purpose of this leaflet is to outline the investigations carried out and the results obtained, and to offer advice on limiting adverse noise effects. (Author/publisher)
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