3: Risk Evaluation and Management: A Road Network Reliability Study

Risk evaluation and management methods are used to assess the reliability of a New Zealand inter-urban road network, which is subject to closures due to snow and ice, earthquakes, volcanic activity and road accidents. Using the probabilities and consequences of closures of various durations, the expected annual costs of closures are determined for each hazard. The benefit-cost ratios for various risk mitigation options are also identified. The importance of considering both the probabilities and consequences of closures is discussed.

It is found that a ‘high-frequency, low-consequence’ hazard (snow and ice) has the highest expected annual cost, and higher than for the ‘low-frequency, high-consequence’ hazards (earthquakes and volcanic activity). It is also found that not allowing for elasticity in the demand for travel (e.g. trips being cancelled or postponed because of road closures) leads to inaccurate estimates of the costs of closure.

It is concluded that it is important to allow for the behavioural responses of network users when estimating the costs of closures, and that more attention should be given to ‘high-frequency, low-consequence’ hazards, in order to maximise the economic benefits of expenditure on risk mitigation.