Measuring skid resistance without contact - 2008-2009 progress report

This report describes the most recent stage of a programme of experiments being undertaken by TRL for the Transport Research Foundation (TRF) to determine whether detailed imaging of the road surface has potential to be applied to the measurement of skid resistance. The ultimate objective of this work is to develop a method suitable for implementation on a traffic-speed survey vehicle. Earlier stages of this project showed the possibility of determining skid resistance from images of laboratory samples of aggregate when they are artificially polished. Some success has also been demonstrated when comparing image-derived parameters with skid resistance on a continuous length of road surface. The work described in this report sought to build on that successful comparison by collecting a large number of images on the TRL research track, from a moving vehicle, and comparing parameters derived from them with skid resistance measured by more conventional means. In addition to use of the algorithms developed in the previous stage of this project, a review of alternative roughness calculation methods that might be applicable to image intensity variation was carried out, and several alternative parameters were implemented in analysis software. Initially, some agreement between the image-derived parameters and measured skid resistance was observed. However, it was found that parameter values were very sensitive to variations in the level of focus between images. Although a post-processing technique to identify poorly focussed images was trialled, the comparison of image-derived parameters with skid resistance requires much better quality, or consistent, images. Further research into the theoretical basis of assessing skid resistance from a road’s surface texture is suggested.