Use of Coloured Surfacing in Roads’ Construction

New materials have allowed different coloured surfaces to be achieved, and the introduction of thin surfacing allows colour to be applied to existing surfaces. With these innovations, it is now possible to make use of surface colour.

There are several benefits of applying coloured surfacing in a number of situations. The purposes/ benefits of coloured surfacing are explained below:

• Coloured surfacing supplements the prescribed signs/markings; to improve contrast of road markings and discourage vehicles from encroaching on an area of road.
• Coloured surfacing is often used to give greater conspicuity to areas that are hatched, as being areas that should not be entered by vehicles unless it is considered by the driver to be safe to do so.
• Coloured surfacing is often applied to bus and cycle lanes in an effort to improve compliance.
• The evidence from schemes where coloured surfacing has been used indicates that the effect of colour may benefit other measures implemented to improve safety or operation. Indications from sites, where coloured surfacing has been used in association with road signs/markings on non-trunk roads suggest that coloured surfacing has contributed to a reduction in vehicles speeds.
• Coloured surfaces are mostly used in combination with road signs/markings. At junction improvement schemes and on links which have a particularly poor accident record, coloured surfacing has been shown to yield a high accident saving when it is used in combination with other measures.

Examples, where coloured surfacing can be used

• To indicate changes in the road cross-section (e.g., where a dual carriageway is reduced to a single carriageway).
• On the approaches to a junction where conflicts between overtaking, through and left turning vehicles have given rise to an accident problem.
• The emphasis hatch markings along the centre of the road, where overtaking accidents are a particular problem.
• A limited application on non-standard hard shoulders and central reserves on expressways.
• On hard areas adjacent to the running surface to deter over-running.
• To emphasis hatch markings on a segregated right turn lane or subsidiary deflector island at a roundabout.
• At side road junctions (e.g., ghost islands) to encourage correct positioning of cars turning into the main carriageway, or at ghost islands which exclude areas of the road but may accommodate long lorries, where the road at the junction is of sufficient width.
• High friction surfacing is applied to carriageways on the approach to bends, roundabouts, signal controlled junctions or pedestrian crossings. Although this is often of a light colour, its primary purpose is to reduce the risk of skidding. However, in these situations it can also highlight the change in the road layout.

Environmental Considerations

• The choice of colour should be made with regard to wider environmental considerations. In urban areas there are more natural colour variations due to the effect of building materials and lighting. These will vary depending on the locations. A balance between the benefits and aesthetics should be considered.
• Standard white road markings will generally be used in combination with the coloured surface, and it is important that the overall visual effect should be considered.
• Coloured surfaces may have different noise characteristics from adjacent surfaces. Therefore, in considering their use near residential properties, the possibility of noise nuisance should be taken into account.
• Coloured surfacing adds to visual intrusion and should not be used by default. It should be reserved for situations where it is considered that it will have a particular safety benefit and where it outweighs the aesthetic disadvantages. Studies have shown that coloured surfacing can reduce the number of vehicles overrunning hatched areas, but the effect reduces with time as the colour fades.

Maintenance Considerations

• The maintenance cycle for surface dressing should be compatible with that of the applied road markings. For mixed-in wearing course materials however the design life of the road will generally exceed that of colour life.
• It is highly unlikely that the colour life of a surface will be as great as the service life. All coloured surfaces will undergo traffic and environmentally induced changes in appearance. Colour restoration techniques will only be economical if the pavement and surface have sufficient service life left (structural strength, texture depth and skid resistance) to warrant the maintenance costs.
• Application of coloured surfacing to the full length of a cycle or bus lane may impose long term maintenance requirements.
• During maintenance it would be beneficial to match the colour of any reinstatement with the surrounding surface. Extra effort should be taken to maintain the appearance and hence the benefit of colour.
• Applied materials should be capable of being removed from the road surface using standard equipment without causing permanent damage to the carriageway, or reduction in residential life of the pavement. It may not always be possible however to remove the applied material without causing damage to the underlying road surface, therefore it will be necessary to take into account the resurfacing costs, when considering applying coloured surfacing on a trial basis, should the applied material be removed following the trials.

Coloured Slurry Seal Systems

A pigmented emulsion slurry seal is used with the appropriate coloured aggregate. This, as with the resin systems, is a thin veneer coloured surfacing, varying in thickness from as little as 1mm. up to 5mm. depending on the aggregate grading.

In the UK all coloured slurry surfacing shall be approved by the Overseeing Organisation. Slurry surfacing should be produced in accordance with BS EN 12273. In some cases, a British Board of Agreement HAPAS Road and Bridges Certificate is required. All coloured materials whether using bituminous emulsion or specially formulated light-coloured binders should be specified using the appropriate end performance criteria. Accelerated ageing and weathering tests with colour identification tests have been developed to demonstrate colour retention by BBA/HAPAS. The coloured Slurry Surfacing should have adequate skidding resistance. As they are usually fairly thin it is not possible to provide deep macro texture. Coloured materials shall retain their colour, to at least to the level detailed in the Certificate throughout the guarantee period.

Hot Rolled Asphalt Surface Course and Suitable Coloured Aggregate for the Pre-Coated Chippings

Specialised Surfacing

There are on the market highly specialised products, with very distinct colours and textures, which although providing excellent colour properties can be ruled out in general highway maintenance situations due to very high cost, or the low quality of the properties of the aggregate in relation to those that are needed to withstand normal road trafficking. These materials can be considered to enhance the look and feel of pedestrian areas in town and city situations where small areas of these materials can contribute a pleasing visual impact. It may be worth considering a policy where conventional bituminous mixtures are used for pedestrian and vehicle areas, these being the areas that take all the load and wear. Future maintenance costs would then be much reduced, and your high-cost-coloured areas would have a much longer life, and as already mentioned you are able to use coloured aggregates not suitable for trafficking.

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