Traffic calming schemes in Great Britain use various measures to slow the traffic. The most effective at reducing speeds usually involve some form of vertical deflection, normally in the form of a road hump or raised table. Humps and raised tables are now permitted to be 50 - 100 mm in height and can have flat-tops, in addition to the more common circular profiles as allowed under the original Regulations. This report describes the types of vertical deflections which can be used, together with an assessment of each, in order to assist Local Authority engineers to decide which is the most appropriate measure for a given situation. Up to now the only estimate of the effect of hump spacing on speeds available to the local authorities (apart from their own and other known schemes) was published in 1987 (Department of Transport, 1987) and was based on work carried out before this date. This report gives an updated speed/separation relationship which indicates that, for a given speed, the separation between humps is now less than that previously predicted. An analysis of accidents has shown these have been substantially reduced at a selection of sites where humps or tables have been used. (A)

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