A systems-thinking approach to improving the freight performance of New Zealand’s state highway bridges

Abstract

A significant proportion of the world’s bridges are unable to support the modern load demands placed on them. As an example, because of the 2010 amendment to the vehicle mass and dimension regulations, 18 % of New Zealand’s bridges are now functionally obsolete. The inability to support modern loads impacts the efficient movement of freight, and thus the economic efficiency of the country where the bridges are located. Accordingly, it is imperative that these bridges are effectively managed. To address the network level problems created by functionality obsolete bridges, a systems-thinking based asset management framework was created. The framework comprises an agent-based bridge asset management model and an integrated system of performance measures. By creating the new model, the use of agent-based asset management models is furthered, as the new model focuses on bridge strength rather than pavement condition. The new model also incorporates a national highway network, which was not present in the existing agent-based asset management models. The addition of a national highway network also furthers the development of bridge asset management models, as these models have typically only incorporated small numbers of bridges on a localised network. The bridge model comprises a set of bridge agents, haulier agents and a decision-making agent. In the model, the haulier agents adapt to the bridge strengthening strategies proposed by the decision-making agent. This adaptation, in combination with a newly developed genetic algorithm, is then used to identify bridge strengthening strategies that maximise the highway network’s functionality. Using the model, the maximum identified benefit-cost ratio was achieved for a budget 94 % less than the budget identified by the planning agency. Alternatively, when the same budget as the planning agency was used, the model increased the benefit-cost ratio by 250 %. Thus, the model provides valuable new insights in to potential network level bridge strengthening strategies. To support the implementation of the identified bridge strengthening strategies, the bridge asset management model was used as the basis for deriving a system of performance measures. By integrating the computational model with a system of performance measures, an organisation can use the integrated framework to rationally identify bridge strengthening strategies and can subsequently monitor the success of the identified strategies. Consequently, the integrated bridge management framework provides a solution for managing the world’s functionally obsolete bridges.