Roads: now available in all colours
Across Europe, the use of coloured asphalt in road tunnels has helped to cut lighting costs without compromising driver safety. James Freeman, Tarmac national special products manager, highlights the potential for UK local authorities to adopt this approach before they hit the 'dimmer switch'.
Highways carbon management and a greater need to cut operational costs have cast the lighting of UK roads into the spotlight.
The Highways Agency's proposal to turn off the lights on a stretch of the M5 motorway after midnight until 5am has been met with a mixed response from road safety groups. Meanwhile, a report by the County Surveyors’ Society (CSS) has stated that the installation of remote monitoring systems to control the level of lamps when roads are lightly-trafficked could save local authorities up to £35 million annually.
Should local authorities reach for the 'dimmer switch' now? The CSS report certainly offers an interesting approach which I believe warrants more feasibility testing. However, if a local authority is set to adopt part-night lighting, there needs to be careful consideration and detailed evaluation of accident statistics for a specific road.
I believe that maximising existing technology to reduce lighting costs and improve driver visibility is also important. Reflective road surfacing technology has the potential to combine with lighting technologies to deliver better driver visibility as well as offering the potential to reduce lighting costs.
One option available to local authorities is light-coloured asphalt pavements. In Europe, there is a strong body of evidence to demonstrate that coloured asphalt in road tunnels has helped to reduce lighting costs and improve driver visibility. It has the potential to be adopted as part of a wider package of measures to reduce energy and lighting bills because of the increased clarity it can provide.
A spotlight on European savings
According to reports from Colas Geneve*, light asphalt surfaces in tunnels can deliver lighting savings of up to 30 to 40 per cent. In the Confignon Tunnel, near Geneva, Switzerland, field trials showed that one spotlight out of two could be turned off because of the increased luminance of the surfacing. Within this project, savings made on lighting have meant that additional capital costs for resurfacing were recouped within just four years.
Data sourced from the International Commission of Illumination on driver visibility and luminance performance from coloured asphalt pavements against other materials is also strong. A three-month study conducted by the International Commission of Illumination across several pavement types, reveals that light coloured asphalt delivers the highest specular reflection factor and luminance coefficient of any material. While conventional asphalt does not pose any driver visibility concerns, the clarity value of clear asphalt is excellent.
Clarity per pavement type
| Pavement type | Clarity value |
| Asphalt, dark aggregates | 0.13 |
| Normal asphalt | 0.15 |
| Concrete, dark cement | 0.18 |
| Asphalt, clear aggregates | 0.18 - 0.24 |
| Concrete, white cement | 0.24 |
| Clear asphalt | 0.3 - 0.4 |
Source: International Commission of Illumination
Light-coloured asphalt is also as durable as the traditional 'black stuff'. Adding quartzite aggregate, light coloured pigments and high-quality polymers with binders to enhance the mechanical stability of the asphalt mix ensures it is suitable for all heavy trafficked areas.
Opportunity in the UK
In the UK, the full potential for light-coloured asphalt has not been realised. Typically, it has been used to demarcate areas such as bus and cycle lanes. But the material's luminance properties and durability when a polymer modified binder is added offer wider opportunities for surfacing in specific areas including tunnels, at intersections and roundabouts as well as on the approach to junctions on unlit rural roads.
In order to provide local authorities with a high-quality, light-coloured asphalt, Tarmac has developed Mastertint. It provides all the qualities of conventional, asphalt with pigment to ensure that the colour is retained throughout the product.
Mastertint - the technical lowdown
Tarmac Mastertint is mixed and formulated in line with the same principles as conventional asphalt but combines cellulose fibres and pigments with Shell Mexphalte C, a clear synthetic bitumen binder from Shell Bitumen. Mexphalte C incorporates polymers that deliver durability and performance in heavily trafficked applications.
Typically, an asphalt mix design study is conducted in the laboratory in order to determine the ideal mix of aggregate, filler and bitumen and to ensure whether mechanical results are in line with relevant asphalt mix standards.
The manufacture and laying of coloured asphalt requires special care. Mixing, laying and compaction equipment must be well-cleaned prior to use in order to maintain a uniform colour for the final mix.
Reducing energy, improving visibility
If local authorities are set to embark on part-night lighting operations they need to ensure that road surfacing is working to maximise visibility for drivers. While light-coloured asphalt is not the sole answer to cutting costs and carbon across local authority roads, it could work as part of a wider package of measures in specific locations to reduce costs, drive down carbon emissions, increase visibility and improve road safety. This technology has delivered proven results in Europe. The road to cutting costs and emissions starts with maximising the technology we already have.
The table below shows the change in surface characteristics of this pavement together with the luminance coefficient and the specular reflection factor over a twelve month period.
| 3 months | 6 months | 12 month | |
| Texture depth, in mm, by sand patch test | 1.5 | 1.2 | 1.2 |
| Luminance coefficient, Qo | 0.130 | 0.125 | 0.117 |
| Specular reflection factor | 1.34 | 1.11 | 0.82 |
*A Guzzo, Le Moniteur magazine / 09.93
See more on Tarmac Mastertint
29 June 2009
