Exploring virtual coupling: operational principles and capacity analysis

Author: Egidio Quaglietta
Co-author: Rob Goverde
Day: Aspect Day Two
Session: Innovation and Future Development (2)

The ever-increasing railway transport demand of passengers and goods has been significantly challenging infrastructure managers in increasing the capacity of existing networks which are already close to saturation. Infrastructure upgrades are costly and not always feasible, especially in densely built-up areas. The railway industry is therefore opting to deploy next-generation signalling concepts which can better utilise existing infrastructure by overcoming traditional fixed-block separation so to let trains move closer to each other. Signalling technologies like ETCS Level 3 are being developed to allow separating trains by an absolute-braking distance (i.e. the distance needed to reach a standstill from current speed) by replacing vital track-side equipment with onboard devices for integrity monitoring and dynamic braking supervision. Capacity benefits provided by such a system are however limited for high-speed lines, where distances between trains can reach up to 4-5 km when operating at speeds around 300 km/h. The concept of Virtual Coupling is hence gaining in popularity since it builds on the principle of separating trains by a relative-braking distance, i.e. the distance needed to slow down to the speed of the train ahead. Trains are envisaged to directly communicate to each other via a Vehicle-to-Vehicle (V2V) communication to keep a safety distance and move synchronously in platoons (here called convoys) which can be treated as a single train at junctions to gain capacity. Similar setups have been tested in the road sector for automated cars under cooperative adaptive cruise control, however non-negligible safety issues arise for railways that could compromise capacity benefits of Virtual Coupling in interlocking areas. Safety risks are especially at diverging junctions where points might not have enough time to safely be moved and locked in between consecutive trains. Principles to safely regulate convoy merging/diverging operations under Virtual Coupling have not been defined yet and only little research has been done to identify impact of safety constraints on capacity benefits of Virtual Coupling. This paper contributes to a wider understanding of this signalling concept by introducing preliminary operational principles for safe train operations under Virtual Coupling and analysing potential impacts on capacity. An infrastructure occupation capacity model for Virtual Coupling has been developed by extending the blocking time theory with defined operational principles. The model has been implemented in the microscopic railway traffic simulation tool EGTRAIN for a detailed capacity computation by means of the UIC Code 406 method. Capacity gains provided by Virtual Coupling have been compared to ETCS Level 3 for different service scenarios. Results obtained for a railway corridor on the South West Main Line in the UK provide useful insights for the railway industry to support early investment decisions on V2V-based railway technologies.