The application of Building Information Modelling (BIM) in tunnel construction is increasingly widespread, yet the impact of varying Levels of Detail (LoD) on project performance remains insufficiently understood. This paper explores how different LoD stages influence tunnel design, cost estimation, and construction efficiency. Through a quantitative analysis, the study highlights the challenges of balancing detailed modelling with the extra time and resource demands it entails. Results indicate that while higher LoD enhances decision-making, it also introduces greater complexity, especially during early design phases. A staged approach is therefore proposed, beginning with simpler models and gradually incorporating more detailed ones as the project advances. The research also underscores BIM’s role in fostering collaboration and minimizing errors. The paper concludes by advocating for phased LoD adoption, targeted BIM training, and coordinated efforts across the industry to develop the best practices for managing BIM and LoD in tunnel projects. This strategy aims to improve project efficiency and mitigate risks such as cost overruns and schedule delays.