Following the amendments in 1992 to the Highways Act 1980, local highway authorities are now able to apply to the Department of Transport (DOT) to use a wider range of measures for speed reduction and traffic calming purposes. This Project Report gives results from a trial of such measures undertaken by TRL. Three basic types of humps were tested, those intended for roads with 40mph speed limits, 30mph limits, and 'speed cushions'. The speed cushions are intended to allow free passage to large vehicles, especially buses, yet constrain the speeds of cars. Vehicles tested included bicycles, motorcycles, cars, buses, commercial vehicles and emergency vehicles. Two methods of assessment were used: drivers and passengers evaluated the effect of the humps on a scale of discomfort; peak vertical acceleration ('g') forces were measured by means of an accelerometer strapped to the lap of subjects. The opinions of drivers, passengers and observers were also taken into account. The trial indicated that neither of the 100mm high, 8 metre long humps tested for faster roads would be suitable. Tests of the series of four 50mm high, 900mm long circular profile humps intended for 30mph roads suggest that discomfort levels at the humps do not meet the criterion of a substantial increase in discomfort as speed increases. The humps were also criticised at the TRL trial for being too harsh and liable to cause damage to vehicle suspensions. Tests of the six designs of speed cushion indicated that a design with height 75mm, plateau width 1400mm, on/off ramp slope 1-in-8 and side ramp slope 1-in-4 would give the least effect on buses whilst still causing discomfort for car occupants. On-road trials of a variety of humps are being carried out at York, Sheffield and Wakefield. (A)

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