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This research project, which was undertaken between 2003 and 2006, aimed to improve the understanding of the effect that environmental factors (eg rainfall and detritus) have on the variation of measured skid resistance, both in the short and longer term. Phase 1 of the research was a field study of seven sites in the Auckland and Northland regions over 2.5+ years, with regular skid resistance measurements primarily utilising the GripTester. Phase 2 involved developing a new laboratory-based accelerated polishing device and methodology for testing large (600 x 600mm) chipseal surfaces with the Dynamic Friction Tester.

Phase 1 results demonstrated that significant and previously unpredictable variations (greater than 30%) in measured skid resistance could occur over short time periods. These variations were the result of a number of interrelated factors, including the geological properties of the aggregates and the contaminants themselves.

Phase 2 results demonstrated that large aggregate samples could be prepared for accelerated polishing tests in the laboratory and that significant variations in measured skid resistance could be achieved by the addition of contaminants and simulated traffic action. Significant behavioural differences were related to the geological properties of the aggregates, as well as the contaminants used in the accelerated polishing process.

Further research is proposed to investigate a greater sample of geological and artificial aggregates, and ‘mix designs’ that may lessen the variation in measured skid resistance during the surface asset life and subsequently improve the prediction and safety performance of surfacings in the long term.

Keywords: aggregate polishing, contaminants, macrotexture, microtexture, rainfall, road safety, seasonal variations, skid resistance, skid testers