Explaining Cost Overrun Causation in Transport Projects: Drawing on Evidential Pluralism to Develop Theory

Cost overruns in transport projects are a problem for governments worldwide. Despite the wealth of research that has sought to explain cost overrun causation, with theories such as the Planning Fallacy and Fifth Hand being propagated, they fall short in being able to substantiate their causal claims. However, a theory’s robustness and reliability depend on the quality of evidence used to cultivate its development and scope, which prevailing cost overrun theories propagated in the literature fall short of providing. In this paper, it is suggested that Evidential Pluralism—a theory about the epistemology of causation—whereby the evidence of mechanisms and correlation are treated equally to assess causality, is needed to build a stronger epistemic foundation for prevailing theories of cost overrun causation in transport projects and enable the development of new ones to emerge. Thus, this paper contributes to establishing the need for a comprehensive and well-supported evidence-based theory of cost overrun causation, enabling policymakers to confidentially make better decisions to manage the risk and uncertainty associated with their transport project costs.