The most effective forms of traffic calming measure usually involve some degree of vertical deflection. Road humps have proven to be highly effective at reducing vehicle speeds, but discomfort to drivers and passengers is increased, particularly in larger vehicles such as buses, lorries, fire engines and ambulances. Speed cushions are designed to limit the vertical deflection of large vehicles with wide track widths by allowing these vehicles to straddle the cushions. Vertical deflection for smaller vehicles, such as cars, with smaller track widths is maintained as these vehicles are forced to ride over the cushions with at least one set of wheels. This report describes a study of 34 local authority speed cushion schemes. It assesses their effect on vehicle speeds, traffic flows, accidents, driver behaviour and passenger discomfort. It considers public reaction to the schemes and the likely impact of cushions on vehicle generated noise and vibration. The effects of differences in cushion dimensions and cushion spacing on vehicle speed are examined and relationships provided. (A)

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