Abstract
This research presents a combined economic and environmental assessment tool for evaluating the economic and environmental performance of alternative maintenance strategies for optimising service life extension of old railway bridges. It is intended to assist bridge managers in identifying the best overall combination of both economic and environmental criteria in their decision making. An approach to assess the potential environmental effect of delaying maintenance work into the future, through the introduction of time-weighting of environmental impacts, is proposed. It is intended to aid railway asset managers to determine the potential benefit or dis-benefit of such ‘delaying’ options, in comparison with ‘non-delaying’ options. The methodology of the tool is based on life cycle analysis and accounts for the cost and environmental impacts that arise during the working life of different alternative maintenance strategies. The economic performance of the alternatives is analysed by using Life Cycle Costing (LCC) whilst the environmental performance is assessed based on Life Cycle Assessment (LCA). The tool addresses the potential unequal working lives of alternative maintenance strategies by evaluating cost and environmental performance through an ‘equivalent annual’ term. The combined economic and environmental performance of the alternatives is evaluated through a multi-criteria decision analysis (MCDA) technique called ‘Single Multi-Attribute Rating Technique using Swings’ (SMARTS). A case study based on typical maintenance plans for a U.K. railway bridge is presented to demonstrate the application of the developed methodology. The three alternative maintenance strategies assessed are deck replacement, standard deck restoration and minor deck restoration. Sensitivity analyses are conducted to account for limited knowledge in some of the input quantities. In summary, this research has shown that the developed combined economic and environmental assessment tool has the ability to identify the best overall performance bridge maintenance alternative and is capable of integrating economic and environmental inputs and presenting the overall performance output in a coherent and transparent way to aid towards decision making. It is believed that it can be of particular use in asset integrity management decisions for assets approaching the end of their original or design service life.