Speed humps are usually installed as part of a traffic calming scheme to help reduce the number and severity of road accidents. They are mostly (but not always) used in 20mph zones where they help to make the lower speed limit self-enforcing.
There are regulations governing the layout of speed humps. Speed humps are designed to maintain slow traffic speeds and cannot be used on their own to slow traffic down. They must be spaced at regular intervals throughout the length of any road to which they are applied and must be within a minimum distance of the entry points to a road. There must also be a form of "slowing feature". Usually this is a change of priority where traffic entering the system has to turn sharp left or right into the road, or has to "give way". Mini-roundabouts, pinch-points and chicanes can all be used at the start of a system of speed humps. Warning signs can be provided to identify speed humps but these are not required where the humps are located within a 20mph zone.
Before introducing any scheme which includes road humps we will consult residents for their views. We will also publish a formal Notice in the press with a three-week period being allowed for objections to be submitted. All formal objections are considered and schemes are revised where appropriate.
Occasionally, we receive opposition to scheme designs from the emergency services (Police, Fire Service, Ambulance Service) and bus companies. The emergency services may have concerns because humps can increase their attendance times for emergency calls which could risk the lives and property of residents. The Ambulance Service and bus companies may have concerns because of the discomfort and possible injury that may be caused to their passengers. Buses in particular may have to go over numerous speed humps on regular service routes and this may increase wear and tear on these vehicles.
Speed hump alternatives
There are a variety of speed hump designs that are regularly used, often in combination within the same scheme:
Round or flat-top speed humps
The shape of speed humps is strictly regulated. They must be between 50mm and 100mm high, at least 2.75m long and extend over the full width of the road, except for a drainage channel at either end. They may have either round or flat tops.
Many local authorities have adopted 75mm high humps as standard. This is because they have been found to reduce traffic speeds to around 22mph. 100mm high humps can reduce speeds further but they may cause excessive acceleration and braking between the humps which can increase pollution. Speed humps can lead to complaints about increased noise and sometimes increased vibration from traffic. They have however been proven to reduce traffic speeds. Speed humps have been installed in many locations.
Flat-topped humps can be of any length and are often known as "speed tables". They are sometimes used to reduce the impact on long wheel base vehicles such as buses. Speed tables are often constructed the full width of the carriageway so that they can provide a useful crossing point for pedestrians. The approach and leaving gradients to speed tables can be designed to moderate approach speeds. The gradients are generally installed at 1in10 but can be reduced to 1in15 on bus routes.
In effect these are speed tables located within a junction which can in some cases include a mini-roundabout.
These are smaller versions of the standard speed hump which will usually be positioned in pairs, one in the centre of each carriageway. On wider roads, three cushions may be used rather than two. They are wide enough to allow wide wheel base vehicles, eg buses and fire engines, to pass unhindered. Smaller wheel base vehicles, such as cars, have to have at least one set of wheels partially on the cushion. This helps to slow cars down without having an effect on other traffic. Speed cushions are often the preferred traffic calming solution for emergency services and bus companies. However, on occasions it is necessary to also introduce waiting restrictions. This is to avoid adjacent parked vehicles diverting passing traffic out of alignment with the cushions. Many local authorities have adopted 75mm high speed cushions as standard.
'Dummy' speed cushions
A number of speed cushions within any traffic calming scheme can be installed without any physical height. These "dummy" cushions only provide a visual deterrent to speeding so arenot used that often. However, they can reduce the degree of inconvenience in larger area-wide schemes.