Project complexity and cost escalations in the early design of railway megaprojects

Large railway projects suffer from major cost overruns and delays, partly due to project complexity. This study explores how such complexity emerges in the early design stages and affects the project outcomes. Data from 14 interviews were compared with four project complexity frameworks. The results indicate that complexity is mainly institutional rather than structural. Optimism bias, fragmented requirement governance, and weak coordination create self-reinforcing loops of cost growth, showing that governance and decision processes, not technical uncertainty, drive early-stage complexity.