Traffic calming

A speed bump (also known as a speed cushion) is a short raised rounded section of road in the centre of a road lane. It’s like a speed table but has a raised section with a gap between them. 

Speed tables are more effective than speed cushions in reducing speeds. Speed cushions allow wider vehicles to straddle the cushion allowing buses and emergency services to pass along a route. Speed cushions are designed to be wider than a car so car drivers will need to slow down and drive over the centre of the cushion to reduce discomfort. 

Speed cushions can be an effective way to reduce speeds. However, they aren’t an appropriate form of traffic calming for entry speeds. as they can result in late braking and a risk to motorists loss of control. Speed cushions may create noise and vibration which could impact local residences. The presence of speed cushions may cause traffic to divert to other routes. To meet the Department for Transport’s (DfT) guidance, multiple sets of cushions need to be installed on each approach. Installing speed cushions in residential areas requires suitable street lighting throughout. 

Due to the impact on pollution, central government is looking for local authorities to reduce the use of speed cushions. This includes removing them where appropriate which would make it harder to justify installation.

Speed tables (also known as junction tables when placed at a junction) take the form of a raised section that spans the road. They achieve significant reduction in speed, making it easier and safer for pedestrians to cross the road on the top of the table where speeds are at their lowest. 

Traffic calming techniques work best when they're installed as a series of tables along a length of a road rather than at one single point.

Speed tables may create noise and vibration which could impact local residents. They may cause traffic to divert to other routes, where a route is regularly used by larger vehicles and/or trailers. Therefore careful consideration would be given to their location.

Drainage impacts would also need to be considered in the design of a speed table.

Priority narrowing involves introducing road narrowing which creates a one-way priority system at that point. The speed reducing effect relies on the regular presence of oncoming vehicles. Traffic without priority has to periodically give way and consequently reduces its speed.

Success with priority narrowing and priority chicanes can be difficult to achieve. Their placement depends on good visibility from approaching drivers. The presence of private drives and side roads also restrict the opportunities where priority narrowing can be placed.

Priority chicanes can take the form of a set or various sets of carriageway narrowings. Groups of chicanes are normally placed with alternating priority along a road. Each direction of vehicle traffic has to stop and give priority in equal amounts. The narrowing(s) can allow two-way traffic flow or can give priority to drivers travelling in a certain direction like with priority narrowing. The aim of chicanes is to break up the traffic flow and so reduce vehicle speeds.

Success with priority narrowing and priority chicanes can be difficult to achieve. Their placement depends on good visibility from approaching drivers. The presence of private drives and side roads also restrict the opportunities where priority narrowing can be placed.

Priority chicanes don’t cause any vehicle passenger discomfort in comparison to vertical treatments. Also, some designs may allow cyclists to bypass them.

Vehicle activated signs (VAS) are electric signs which display a message or speed when triggered by vehicles travelling at excessive speeds. The signs can display the speed limit or they can warn drivers of an approaching hazard. VAS supplement rather than replace the traditional signs and line and address specific road safety problems.

A vehicle activated sign should be used strategically where they will have the maximum effect.

Rumble strips (transverse bar markings) are designed to provide a visual, sensory warning to drivers on high-speed approaches to roundabouts and high accident frequency locations.  

When used in the correct layout, rumble strips have been proven to be very effective against accidents associated with excessive speeding. 

These normally take the form of a series of slightly raised strips of different coloured surfacing, set across the width of the road.  

The appearance and feel of the strips are intended to cause drivers to reduce their speed.  

Due to the resulting road noise which can be experienced by nearby residents, the locations where rumble strips can be effectively used are limited.  

Rumble strips are not normally laid within 300 yards of residential properties. 

Speed limits state the maximum speed permitted on a given road. The speed limit is displayed at the beginning of the section of road, inside a circular sign. Carriageway roundels are hardwearing markings that indicate the speed limit on the carriageway. The marking is varied to show the speed limit in force and elongated in the direction of travel to compensate for the foreshortening effect.

Carriageway roundels can’t be:

• used as a repeater in a street lit area

Carriageway roundels can be:

• used as a repeater for 20, 40 and 50mph speed limits (not to be used on 30mph speed limits).

Carriageway roundels are normally installed in pairs and can be co-located with a terminal sign at the start of a speed limit.

Speed limits as low as 20mph should normally be introduced with extensive traffic calming measures (e.g. speed tables, and speed bumps) to ensure that speeds are in compliance with the limit, or where speeds are already low.

When considering the appropriate speed limit, other factors must be assessed as installing the wrong speed limit on a road will mean it won’t work properly. The speed limit must be appropriate, taking into account all the road’s characteristics and the surrounding environment, such as whether the locality is a built up area, near a school or a town centre.

20mph zones have generally been considered in residential areas to keep speeds low.

A build-out is a section of kerb/footway extended out into the carriageway on one side only to narrow the road. They can reduce crossing distances and improve visibility for pedestrians. If the space is available, a gap can be left between the pavement and the build out to form a cycle bypass.

It is particularly beneficial near parked cars (see sheltered parking) but can also be used as part of a chicane system (see priority chicanes and priority narrowing above).

Build-outs can be difficult to achieve where there are many private driveways restricting their positioning.

Village gateways are usually found on the approaches to built up areas where the speed limit signs and town/village nameplates can be incorporated to give maximum impact to approaching drivers.

The signs may be placed on high profile backing boards and when introduced with new road markings, remind drivers that they are entering an area which requires extra special attention.

A road traffic message may also be included with a maximum of 5 words.