Types of traffic calming and other engineering measures

Lowering speed limits alone may not have the desired effect. National guidance advises that 20mph speed limits should be self-enforcing. Sometimes it is necessary to install traffic calming measures to encourage compliant speeds.

Road humps stop people speeding up rather than slow them down. Extra slowing features at each end of a run of humps will be provided. They are suitable for residential areas but are not acceptable on bus routes. Effectiveness decreases as spacing increases.

Raised rectangular areas. There can be one, two or three, depending on the width of the road. Like humps they are most suitable for built up areas and need slowing features. They do not slow speeds to the same extent as humps but do give emergency vehicles and buses a smoother ride.

Like road humps but longer and with a flattened top. Sometimes used to give pedestrians a level crossing between footways. They can also be used throughout a junction. Especially useful where there are a lot of pedestrians. If they are long enough, they provide a smoother ride for buses than humps.

Localised widening or construction of footway can narrow the road and slow traffic. They reduce crossing distance and improve visibility for pedestrians crossing the road. Placed alternately they provide chicanes. Roads can be narrowed to such an extent that only single file traffic is allowed. They can also provide sheltered parking. Suitable for use in urban or rural locations, as slowing features or part of gateway features. Single lane build outs are not suitable for roads with high traffic flows.

Narrowing lanes, using traffic islands and/or road markings can give the impression of a more confined road and result in reduced speeds. If a road is narrowed special attention must be given to the needs of cyclists.

There are many ways to define a gateway or entry point:

• Road markings
• Build outs
• Coloured surfacing

Signage indicating changing road conditions (for example change of speed limit). Most effective on those drivers that only use the road occasionally.

Often used as part of gateway schemes. Rumble strips are a change in the road surface which alert the driver by a change in the sound and feel of the car. Dragon's teeth provide a visual change and narrowing of the road. They are suitable for village entry points. Because rumble strips generate noise they can be unpopular with residents.

Crossings may encourage more people to walk by improving safety and reducing delays crossing busy roads. They can be provided where there is a concentrated crossing movement, but there does need to be adequate visibility.

Refuges allow pedestrians to cross one stream of traffic at a time. They are useful where the concentration and number of pedestrians is low. By narrowing the road, they reduce speeds. The road needs to be wide enough to allow for a suitable refuge and the safe passage of vehicles and cycles.

Equal priority in all directions can slow traffic. There needs to be a reasonably large flow on all arms for this to be effective. Roundabouts can make some turns easier which can lead to rat-running. They can be expensive and also need works to slow traffic down on the approach to the roundabout. Mini-roundabouts take up less space but need to be in street lit areas.

Control the circulation of traffic but can lead to faster speeds as there is no opposing flow. Traffic can increase on other roads so there needs to be a suitable route for traffic travelling in the other direction. One way streets can attract new traffic so traffic may not decrease. 

These provide the ultimate deterrent to rat running but can be unpopular. They sometimes cause long diversions and increase traffic on other roads. Emergency access and the needs of services need to be considered.

These can help to manage traffic (i.e. Protected Parking Bays). Double yellow lines maintain traffic flows in urban areas. Time restricted parking allows access to facilities within towns/villages. It also alleviates the problems associated with long term parking. Can be unpopular with residents and businesses. Parking problems can transfer to other roads.

Signs alone have a minimal impact on traffic speeds but are low in cost. They are often used with other traffic calming features.

Interactive Signs

These detect the speed of oncoming traffic using a radar device. If a set threshold is exceeded, a sign indicating a specific hazard or speed limit is triggered. They can be temporary or permanent. 

Pedestrian safety and comfort can be enhanced by improving footways on the pedestrian network. The introduction of a missing footway link may encourage more people to walk. The highway needs to be wide enough to allow for a suitable footway and safe passage of traffic. The provision of dropped kerbs and tactile surfacing may also be appropriate.

Footways can be expensive if utility services or street lighting are affected.