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This report presents the results of a research programme involving both laboratory and on-road investigations that has been carried out in 1996–97 with the aims of:

• improved understanding of the Polished Stone Value (PSV) test and its application to alluvial aggregates
• identifying critical aggregate characteristics from the perspective of skid resistance performance
• calibrating Transit New Zealand's stationary laser profilometer so that the speed number component of the International Friction Index (IFI) can be determined for New Zealand roads.

The experimental design used together with significant correlations identified between skid resistance and aggregate and surface profiles are described.

The principal finding of the research was that the crushing process beneficially affects the polishing resistance of greywacke alluvial aggregates by exposing a greater degree of microtexture and also on-road skid resistance by increasing texture in the 1–5 mm wavelength range. Texture at this scale is a significant contributor to the hysteretic component of tyre rubber friction.

Two predictive skid resistance models are presented, one relating skid resistance to easily measured seal characteristics, and the other to road surface profiles over 0.5 to 50 mm wavelengths. Both models were capable of explaining 75–80% of the total variation observed in the GripTester derived wet skid resistance values.

Keywords: aggregates, alluvial aggregates, crushing process, International Friction Index, modelling, pavements, predictive models, polished stone value, road, road texture, skid resistance, surface profiles