Preparing a Traffic Calming Scheme
Traffic calming uses specific measures to reduce and control vehicle speeds to a level commensurate with the activities taking place along a road. It can also encourage drivers to adopt a uniform speed without excessive acceleration or deceleration. In addition, traffic calming can be used to influence driver behaviour towards non-motorised road users.
Traffic calming has mainly been used in urban areas on roads with speed limits of 30 mph or less. This has reflected the predominance of these lower speed roads in the urban environment and the much higher proportions of accidents involving non-motorised road users.
While safety may be the primary factor in justifying a traffic calming scheme, the local environment, community severance and accessibility issues are all acceptable reasons for introducing traffic calming on trunk roads.
In some instances, conflicts can arise between achieving appropriate speed reductions and reducing the visual impact of the measures on the surrounding landscape. Obviously a balance must be struck, but designers must be aware that compromises in the design of traffic calming measures may result in a less than effective solution. In particular, less speed reduction might be obtained and this must be taken into account fully when informing the public as to the likely effect of a particular scheme.
High proportions of heavy vehicles will have a significant effect on the measures to be employed when designing traffic calming scheme for trunk roads. Proposals must take into account vehicle noise, vibration and turning areas required for larger vehicles.
Techniques for Traffic Calming
There is a range of traffic calming techniques that fall into the broad categories of:
- Physical measures such as horizontal and vertical deflections which encourage drivers to reduce speed by a sharp change in the vertical and/or horizontal alignment which causes discomfort when travelling at higher speeds; and
- Non-physical measures that encourage adjustments in driver behaviour such as speed cameras, vehicle activated signs, textured surfacing, speed limits signs, gateways etc.
Most traffic calming schemes will consist of a combination of physical and non-physical measures. In any particular scheme, the techniques to be used for achieving the objectives should be based on the most appropriate and effective measures.
Scheme Development
An appropriate level of engineering, safety, traffic and environmental assessment should be carried out for all traffic calming schemes to identify constraints and opportunities and inform decisions.
Traffic calming objectives are best achieved by a multi-disciplinary approach. Consultation with road safety officers, landscape architects, planners, police and other professionals can assist in maximising the benefits to be derived from a scheme and easing its passage through public consultation. The range of expertise required will depend on the location, size and sensitivity of the project. However the key stages of scheme development, assessment and appraisal, detailed design, public consultation and monitoring will be appropriate to all schemes to some degree.
It is important to identify the problems to be addressed and to define clearly the objectives for the scheme. This will allow for better assessment of options as well as helping to define the requirements for ‘before’ data. Scheme objectives may include casualty reduction, speed reduction, environmental improvement, and promotion of sustainable modes, accessibility or other community benefits. Different options should be developed.
Pedestrians and Cyclists
In considering the needs of non-motorised users it is important to allow for their needs to cross the road as well as to move along it.
The effect of traffic calming on cyclists should be considered and where appropriate, the design should be modified to accommodate them.
Pedestrian desire lines should be established and traffic calming scheme examined from a walking perspective. Potential obstacles to walking should be identified, particularly for the young and elderly. Consideration of the needs of the disabled should also be included in the design process.
The provision of controlled and zebra crossings and pedestrian refuges assist pedestrians, help to promote walking and can act as traffic calming tools in their own right.
Bus Services
The provision of bus services is an important part of introducing sustainable transport. A balanced approach should be adopted which minimises the impact on bus services whilst achieving the overall objectives of the scheme. In striking this balance due consideration will need to be given to the frequency of the services affected. The siting of bus stops is an important factor as they often result in pedestrians crossing in the immediate vicinity. Bus stops and chicanes should not be sited near to each other as this may cause safety problems for overtaking vehicles. Where a hump is to be placed at a signal controlled or zebra crossing it should be a kerb to kerb flat top hump.
Emergency Services
Emergency services often have concerns about the effect of traffic calming schemes on response times. Therefore the emergency services should be consulted on traffic calming schemes.
Parking and Servicing
Parking and servicing requirements should be integrated in the overall design. Within settlement, opportunities may be available to rationalise parking for residents, shoppers, visitors and service vehicles.
Environmental Considerations
The degree to which environmental considerations should be applied will vary depending on the scale and complexity of the project. Consideration should be given to the potential for partnership with others, the character of the area and any distinctive features, the quality and range of paving materials and street furniture, improvement to existing lighting, noise and air quality implications, planting and maintenance implications.
Drainage Issues
Drainage is an important issue to address, as poorly designed traffic calming features may obstruct drainage channels or change carriageway cross-falls or camber. Where ‘dropped kerbs’ are used, the highway may start to drain on the footway, or cause ponding at newly created low points, which could result in problems for pedestrians and cyclists. A kerb ‘build out’ may prevent a footing from draining towards the cycleway and might also disrupt the flow of water along a carriageway channel, giving an opportunity for ponding in adverse weather.
There may be a need to install new drainage gullies at low points in the highway or the footway, or to change the highway profile to take account of new geometry.
Signs, Marking and Lighting
Signs markings and lighting are used to provide information to ensure that appropriate warning of traffic calming features is given to approaching drivers at all times. Many measures will need to be accompanied by signing to indicate to motorists how they should be used. It is recognised that road clutter and the visual impact of signs can be a problem so the rationalisation of signs and the use of sympathetic lighting systems are recommended. Traffic calming measures need to be visible during both day and night and during wet and dry conditions. It may not be possible to identify colours at night under certain types of artificial lighting. If coloured surfacing is used, it is important that the lighting used to illuminate it has good colour rendering.
‘Desktop’ Study of the Area
A ‘desktop’ preliminary site conditions should be checked against actual site conditions. For example, a 75mm high speed table or road hump is unlikely to perform as intended if the existing kerb is only 50mm, leaving the new feature higher than the surrounding footway. If a flat top road hump is to be installed flush with the surrounding footway, it cannot be simply constructed to the existing footway height. As existing 125m high kerb would result in a hump design that exceeds the maximum permitted height. The footway will normally need to be dropped to be flush with a traffic calming feature. The maximum permitted height for a raised junction is 100mm, bringing it closer to the kerb height but requiring special consideration to ensure an acceptable ramp gradient.