Capacity evaluation of mixed passenger–freight traffic on high-speed railway line

Abstract

The research analyzes the compatibility of railway circulation between High Speed passenger trains and freight trains operating on the same infrastructure, with particular reference to the estimation of line capacity according to International Union of Railways (UIC) methodologies. This represents a case of complex compatibility, dictated by the different mechanical and dynamic characteristics of the rolling stock involved. These differences strongly influence the heterotachicity that must be taken into account both in the design and in the operational management of the line, as well as in addressing the problem of calculating and optimizing the capacity of the railway corridor. The analysis is carried out using the Terzo Valico dei Giovi as a case study, which represents the first Italian High Speed/Capacity line where a truly mixed use of the railway infrastructure for both passenger and freight services is envisaged. The study has been developed by examining different scenarios of mixed traffic circulation through the application of UIC capacity assessment approaches, based on the evaluation of headways, occupation times and timetable stability margins, in line with the principles defined in UIC Leaflet 406. This process leads to the definition of an operational timetable for the line and to the quantification of the impacts on the available line capacity, as well as on train travel times and overall operational performance. The results show that freight capacity is highly sensitive to train mass, dropping from 160 paths (800 t) to 48 paths in other cases. The UIC 406 compression analysis confirms that on high-speed lines, freight train performance and traffic heterogeneity are the main determinants of capacity saturation, as heavier trains significantly increase infrastructure occupation time and quickly consume bottleneck capacity despite temporal separation and advanced signaling systems.