This research investigates the reliability and accuracy of the Environmental Cost Indicator (ECI) in predicting the long-term environmental impact of Dutch infrastructure projects, with a particular focus on the operation and maintenance (O\&M) phase of movable bridges. The ECI is used during tenders to estimate the environmental impact of a structure in a single monetary value, however its predictive accuracy over the asset's lifecycle remains uncertain. With help of a literature review, stakeholder interviews, case study analysis and a sensitivity analysis, this thesis aimed at addressing this knowledge gap.

The results revealed that the ECI provides a rough estimate of the actual O\&M impacts, with discrepancies ranging from 9-16\%, and up to 25\% when considering unplanned renovation. Key limitations of the ECI value included misalignment between time-based assumptions in ECI tools and the condition-based strategy used in practice, exclusion of minor maintenance, incomplete material databases and insufficient monitoring protocols. The results of this study had some limitations that included the small set of case studies and the need for assumptions due to missing data.

To improve the reliability of the ECI, the recommendations included incorporating minor maintenance in standard calculations, expanding material databases, requesting ECI ranges during tenders, improving documentation, integrating environmental impact into asset management methodologies and updating ECI tools to better reflect real-life maintenance strategies. Future research should explore the ECI reliability of other asset types, develop monitoring protocols and investigate the possibilities of an adaptive ECI tool. Improving the ECI's accuracy is critical for supporting sustainable infrastructure development in the Netherlands.