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Roughness indices are used to monitor road condition and prioritise maintenance and rehabilitation programs. The most commonly used measure in New Zealand is NAASRA roughness which is based on the dynamic response of a normal passenger car. It does not necessarily reflect the dynamic response of heavy vehicles which produce most of the pavement wear and hence may not reflect the rate of future deterioration of the pavement. Therefore a roughness index based on heavy vehicle response would provide useful additional information for pavement managers. The report describes attempts to develop such an index.

The International Roughness Index (IRI), determined using a computer simulation of a simplified quarter car passing over the road profile, is used to calibrate NAASRA roughness meters. Thus IRI was used as the reference roughness index for this study. Other indices were generated by: using the IRI model with heavy vehicle-based parameters, replacing the simple spring with a non-linear leaf spring model, and using band-pass filtering directly on the road profile data.

IRI provides a reasonably good predictor of heavy vehicle response, using dynamic wheel forces generated by heavy vehicles, and hence of the road wear caused, than other indices evaluated and tested.

Basing a roughness measurement system on a trailer configuration is suggested as it would have a longer life, be simpler to calibrate, easier to replicate and cheaper. The measurement system should be electronic and computer-based to improve reliability and storage.

Ideally the system should be based on measuring road profiles rather than vehicle response as it could then be used to extract any number of roughness indices merely by changing the analysis procedures.

Keywords: Dynamic wheel forces, IRI, NAASRA roughness, pavement damage, roads, road profiles, road roughness, roughness