Road surface reflectance

This project investigated road surface reflectance characteristics and found that road surface reflectance characteristics need to be redefined. The primary purpose of road lighting is to make people, vehicles and objects on the road visible by revealing them in silhouette against the road surface. As a result, road lighting standards are expressed in terms of luminance. The luminance of any point on a road surface is a function of the illuminance on, and the reflection properties of, the pavement material. The reflection properties of a road surface are given by a reduced reflection coefficient table, called an r-table.

BS5489-1:2003 identifies one set of data for asphalt road surfaces, the representative British road surface, this being CII with the diffuse reflectance Q0 set to 0.070. This is modified to CII with Q0 set to 0,10 for concrete road surfaces. The representative British road surface has been applied for many years to roads constructed with established pavement materials such as hot rolled asphalt and brushed concrete. However, there are now a number of new asphalt-based pavement materials available, such as porous asphalt, stone mastic asphalt and a number of proprietary thin surfacings together with one new concrete-based pavement material, exposed aggregate concrete.

A review of road surfaces was carried out by Steve Fotios in collaboration with Peter Boyce (Independent Consultant) and Cliff Ellis (Sheffield Hallam University) for the UK Lighting Board of the Roads Liaison Group. This review was done using measurements of road surface reflectance reported by TRL in 2000 to compare the effects on lighting design.

It was found that:

• The new and established pavement materials have similar reflectance characteristics, but that both new and established pavement materials tend to have lower S1 and Q0 values than those of the representative British road surface and its modification for concrete surfaces.

• Road lighting installed on either the new or established asphalt-based pavement materials but designed using the representative British road surface will result in an average road surface luminance lower than the BS5489 recommended minimum.

• If lighting were designed using r-tables better matched to the reflection properties of established and new road surface materials this results in an increase in capital costs and annual energy costs of approximately 25%.

It was suggested that the road surface characteristics of the representative British road surface should be modified to CII with Q0 set to 0.050 for asphalt road surfaces and CII with Q0 set to 0.085 for concrete road surfaces.

Publications

• Fotios SA and Boyce PR, Ellis CE, Reflecting current trends, Surveyor Magazine, 13th July 2006; No. 58896, Vol. 194; 16-18.

• Fotios SA and Boyce PR, Ellis CE, The effect of pavement material on road lighting performance, The Lighting Journal, 2006; 71(2); 35-40.

• Fotios S, Boyce P, and Ellis, C., 2005, The effect of road surface material on road lighting performance, Report for the Department for Transport, 2005, contract number PPAD 9/100/77.

• Fotios SA and Boyce PR, Ellis CE, The effect of pavement material on road lighting performance, Local authority Lighting 2005, The Royal Institution of Great Britain, London, 8th December 2005, ILE/Surveyor 2005.