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This study, carried out in 1998, investigates hazards that have the potential to close the Desert Road, which traverses for some 60 km the Central Volcanic Plateau of the North Island, New Zealand, at around 1000 m altitude. It is part of New Zealand's major north-south link, State Highway 1, and it provides a case study for the application of risk assessment methodology to the evaluation of road networks in New Zealand.

The hazards investigated comprise snow and ice, volcanic eruptions and lahars, seismic events, and traffic accidents. A stochastic model is developed for each of the hazards to determine the probability of the hazard occurring and the resulting road closure duration. The vulnerability of alternative routes through the Central North Island, to these hazards is also evaluated.

A traffic assignment model (SATURN) is used to predict the disruption caused by closures of the Desert Road and its alternative routes, and quantifying the economic cost of closures to the New Zealand economy. Monte Carlo simulation is used to find the probability distribution of the average annual cost of closures caused by each hazard. Decision-analysis software, which can be used to determine the spending portfolio for mitigation options that will optimise the risk reduction attained for a given expenditure, is also described.

Keywords: accidents, ashfall, earthquake, evaluation, ice, lahar, mitigation, modelling, natural hazards, New Zealand, risk, risk assessment, roads, road closure, snow, traffic, volcanic events