Application of railway microsimulation models to evaluate investment strategies for single-track railway lines

Railway transport in Europe is currently experiencing a surge, driven by sustainable development strategies. However, rising demand poses significant challenges for infrastructure managers, particularly regarding single-track regional lines, which often constitute system bottlenecks. This article presents a methodology for evaluating and selecting optimal infrastructure investment variants using dynamic microsimulation, addressing the problem of limited capacity and traffic instability on single-track sections. The study utilises OpenTrack software to conduct stochastic microsimulations of railway traffic. The research focuses on a case study of the Poznań – Piła railway line (No. 354) in Poland. Six infrastructure variants were defined and analysed, ranging from the "do-nothing" base scenario, through the construction of passing loops and partial double-tracking, to full double-tracking. These variants were tested under two operational scenarios: a standard periodic timetable and an intensified high-frequency timetable (with a 30-minute interval), applying random primary delays to assess system resilience. Key performance indicators included secondary delays, infrastructure occupation, and delay dispersion. The simulation results demonstrate that the base variant is highly unstable and prone to delay propagation. The study revealed that targeted point investments, such as a strategically located passing loop, can effectively reduce secondary delays by approximately 50% under moderate traffic conditions, offering a high cost-benefit ratio. However, for high-frequency services, partial double-tracking proved insufficient, as it merely shifted bottlenecks to the remaining single-track sections rather than eliminating them. Only the full double-tracking variant guaranteed system stability and reliability under heavy traffic load. The research confirms that microsimulation is an indispensable tool in the investment decision-making process, enabling the identification of potential bottlenecks that static methods often fail to capture. The findings suggest that while partial modernisation is effective for immediate relief, long-term strategies for high-frequency regional connections require comprehensive infrastructure expansion. The study provides practical recommendations for planning the development of regional railway networks to ensure operational reliability.