Road Safety - Speed Humps
A General Guide - Introduction
Road humps were formally introduced in this country during the early 1980's. Their main purpose is to reduce vehicle speed and therefore reduce the number and severity of road traffic accidents. Through traffic may also be reduced. It is worth noting that in a study in 1998 it was found that, where humps had been used, an average reduction in through traffic of around 24% was recorded.
Road humps can only be constructed on roads which have a speed limit of 30mph or less, and have street lighting. Their construction and signing is regulated by the Department for Transport (DfT). There is a requirement to consult with the emergency services, organisations or groups representing people who use the road such as bus operators, other transport service providers and residents and traders of the street where the road humps are to be installed.
An advance speed-reducing feature should be used to ensure that as far as possible the speed limit is not exceeded when the vehicle meets the first hump. This could be a junction or a bend of at least 70°, or give way markings at a narrowing creating priority working, located immediately before encountering humps. Where an advance speed-reducing feature is used, it should be less than 60 metres from the first hump to obtain the maximum benefit. Other than when used as an entry treatment, single road humps are not recommended, unless they can be used in conjunction with other speed-reducing features.
Where a side road leads into a road with road humps, it is recommended that a road hump should be met within a distance of between 40 and 70 metres dependent on traffic flows.
Road humps may only be used where street lighting is present, and, where possible, individual humps should be placed close to a street light.
Spacing Between Humps
It is recommended that road humps should be spaced at between 20 metres and 150 metres apart. The spacing between road humps will influence the average speeds and a spacing of about 70 metres is normally recommended.
Road Hump Dimensions
Road humps constructed to meet the regulations must be between the heights of 25mm and 100mm respectively and have a minimum length of 900mm. To limit the effects of vehicle grounding, it is recommended that the ramp gradients of road humps should not be steeper than 1:10. Other considerations such as inclines, presence of buses, etc. along a route may demand shallower gradients. Humps may either be curved or flat topped. More severe humps, which reduce vehicle speeds to 10mph or less, may be used on private roads, but are not permitted on the public highway.
These are narrow transverse features raised slightly above carriageway level, which are cheaper but less effective than road humps. The maximum height permitted under the Traffic Calming Regulations for a rumble device is 15mm. Due to the noise generated by rumble strips they should not be used near houses. They can be used in rural areas without street lighting.
Pedestrian and Cycle Crossings
Flat top road humps may be used at pedestrian and cycle crossing places. These include controlled crossings, such as Zebra / Pelican Crossings.
Road humps may be used in 20mph zones without the normal road markings and warning signs.
Often the emergency services, public transport providers and other regular delivery services object to the introduction of road humps on routes which they use regularly.
In these cases it may be advisable to use speed cushions, which have a similar profile to road humps but can be straddled by vehicles with a wider wheelbase. Location / spacing guidelines are the same as for road humps.
*This information has been reproduced by kind permission of Bristol City Council