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.
Location
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.
Rumble Devices
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.
20mph Zones
Road humps may be used in 20mph zones without the normal road
markings and warning signs.
Speed
Cushions
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
