an investigation into the overall costs involved in the operation of construction traffic on a pavement sub-base has shown a way of decreasing the cost of construction of the road pavement. the analysis optimises the combined costs of operating the construction traffic and of providing a sub-base of sufficient strength to carry the construction traffic. results show that, for a given sub-grade and haulage distance, an optimum combination of lorry class and payload can be chosen to minimise the total transport and sub-base construction cost. for sub-grade of california bearing ratio (cbr) 2 per cent and haulage distance (for pavement material) less than 26 km an intermediate lorry size (maximum payload 9 mg) gives the minimum cost. for subgrades of cbr 5 or 8 per cent and longer haulage distances, larger lorries become more economical. savings as great as 15 per cent can be made by operating optimal transport rather than the fully loaded large 4-axle lorries commonly used. (a).

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