The Highway (Road Humps) Regulations 1990 and the Road Humps (Scotland) Regulations 1991 allowed considerable flexibility in the use of road humps over previous legislation. They provided for the use of both flat top and round top road humps, and permitted the height to be varied between 50mm and 100mm. The regulations resulted in a large increase in the number of road humps being installed, though these were mainly 100mm high. A consequence was the incidence of vehicles grounding on these humps. The Transport Research Laboratory (TRL) on behalf of the Driver Information and Traffic Management Division (DITM) of the Department of Transport (DOT), were commissioned to investigate grounding problems. In a separate, but related study, TRL compared the effects on speed reduction between lower height (75mm) and full height (100mm) road humps. The investigations revealed that use of road humps with a height of 75mm would substantially lessen the likelihood of grounding. Additionally, when compared with 100mm high humps, little or no erosion in speed reduction resulted, and providing suitable spacing was employed, 75mm high humps would be applicable in 20mph zones. The purpose of this leaflet is to highlight the findings of the studies. (Author/publisher)
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