How reliable are estimates of infrastructure costs? A comparative analysis

Although the economic importance of adequate infrastructure is generally recognised, in practice decision-makers - faced with the judgement of new large infrastructure projects - are hesitant to approve such new projects because of the uncertainty in the related cost estimates. It is often argued by them that expost the actual costs of new infrastructure appear to be usually underestimated. Sometimes even the term 'strategic underestimation ' is used. This paper investigates the causes of misjudgement of infrastructure costs by distinguishing systematically various classes of miscalculations and misrepresentations of costs. Based on a comparative analysis of cost estimates of infrastructure projects in the Netherlands and Finland, the interesting conclusion is found that in general cost estimates tend to be rather reliable. Underestimations are - in addition to inflationary backgrounds caused by the delay of projects over a long time span - mainly the result of additional political wishes in the form of adjustments or extensions imposed during the preparation and implementation stage of projects and which lead to excessive cost rises.