Road humps in the UK can have a circular profile (round-top) or a flat-top with ramps up to the plateau. The most effective humps at reducing vehicle speeds are 100 mm high but, because of passenger discomfort, these are not usually suitable for bus routes or where the emergency services may be expected to have to traverse the humps on a regular basis. Lower heights and shallower gradients reduce discomfort but are likely to increase overall traffic speeds. This report describes a study of 72 sites in the UK where 75 mm high humps have been used and it assesses their effect on vehicle speeds. It gives speed spacing relationships and concludes that 75 mm high humps (with ramp gradients 1:10 to 1:15) can be used to reduce speeds to below 20 mph. Shallower ramp gradients or humps lower than 75 mm high are not so effective and more suitable for keeping speeds to below 30 mph. (A)

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