Is Additive Utility Function Always a Sufficient Method in the Project Prioritization Process? Bridge Management Perspective

The prioritization of maintenance activities in bridges has great importance in bridge asset management systems as they are mentioned in MAP-21. One of the most commonly used prioritization methodologies in bridge management systems is multi-attribute utility theory process. In this study, the problem is defined as using the additive functional form in this process without testing additive independence (AI) assumption, which is one of the properties of multi-attribute utility theory. This study aims to emphasize the strength of the use of multiplicative functional forms when the multiplicative form is proven to be more appropriate by AI assumption test. To demonstrate this vital point, mathematical expressions are derived for the feasible regions of indifference curves. Then, the optimum region for both additive and multiplicative approaches are calculated using these analytical expressions to demonstrate the difference between the two relation to maximizing utility. This comparison is aimed at preventing suboptimal decisions because of the use of the additive approach when the multiplicative approach is more representative of the actual decision-making process. The relevance of this claim is also demonstrated using a simple hypothetical scenario. Findings of the paper provide valuable insights to decision makers and policy makers about the importance of choosing the most appropriate functional form for utility functions employed in a prioritization. We hope that policy makers at state departments of transportation will use the comparative analysis of the effect of utility functions on the final project selection process presented in this paper as part of their routine decision-making process.