This study investigates hazards that have the potential to close the Desert Road, which is part of New Zealand's major north-south link, State Highway 1. It provides a case study for the application of risk assessment methodology to the evaluation of road networks. The hazards that are investigated include snow and ice conditions, volcanic eruptions and lahars, seismic events, and traffic accidents. All of these hazards have the potential to close the Desert Road. For each of the hazards, a stochastic model is developed 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 are also evaluated. A traffic assignment model, SATURN, is used to predict the disruption caused by closures of the Desert Road and its alternative routes, quantifying the economic cost of closures to the New Zealand economy. Monte Carlo simulation is then used to find the probability distribution of the average annual cost of closures due to each hazard. Mitigation options that may either reduce the probability of closure occurring, or reduce the duration of closures, are investigated. The new risk of closure with the mitigation in place is compared to the existing risk of closure, to find the probability distribution of the benefit-cost ratio for each mitigation. A computer based risk optimisation program is described that can help select the portfolio of mitigation options that will optimise the risk reduction attained for a given expenditure.
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