Table 3.
Identified critical aspects with regard to VCTS and suggested mitigation measures.
| Enabler | Critical aspect | Possible solution/mitigation measure |
|---|---|---|
| Brake system | Performance of current SIL4 braking systems insufficient for safe VCTS headway management | Development of SIL4 electronic braking system with improved modulation, accuracy and response time, utilization of closed loop control |
| Handling of low wheel-rail adhesion and brake failures | Utilization of real-time adhesion measurement, permanent brake monitoring and closed-loop brake control. Increased information accuracy to optimize safety margins | |
| Communications | Low latency requirements not achievable with current technology | Latency reduction with T2T communications or simplified fixed network structure. Low latency features promised by future V2X communication standards (e.g. IEEE 802.11bd) |
| Headway between high speed and freight trains requires long communication ranges | Increased transmission power or utilization of MIMO transmission to extend communication range. Simultaneous operation of different technologies to increase frequency specificity | |
| Increased retransmission data rates required, if threshold for the maximal tolerable packet error rate is exceeded | Increased transmission power or retransmission rates, utilization of MIMO transmission or error code correction by combination of several technologies | |
| Availability (marked readiness) of rail certified communication systems | Usage of adaptable communication systems (ACS): achieving redundancy by combination of different systems results in better coverage or optimized dimensioning to support high traffic and coverage | |
| Limited availability of spectrum bands | Utilization of license free spectrum bands (only reasonable in mmWave bands); shared ITS-band (5.9 GHz) usage for railway and road applications; acquisition of license for new railway exclusive bands; consideration of cognitive radio approach with primary and secondary user | |
| Field elements | Current switching technology not suitable for demanding VCTS operation | Development of fast point machines with instant status notification in order to allow general VCTS operation and coupling/de-coupling procedures |
| Level crossing | Technology adaptation to account for multiple consists along the level crossing | |
| Interoperability with existing signaling systems | New coupling scenarios and variable platoon length can be conflicting with current interlocking paradigm | Introduction of new communication protocols and software-based implementation of new scenarios into interlocking rules |
| Presence of two non-physically coupled trains in one section not foreseen in current railway signaling | Adaption of the ATP logic regarding VCTS functionality to prevent stopping of virtually coupled trains | |
| Platforms | Space restrictions at existing stations | Utilization of VC procedures (calling at multiple platforms); adaption of passenger steering to faster platform clearance; optimization or development of new platform layouts |
| Traffic management system | Functional architecture of VCTS and TMS interactions undefined | Software based definition of VCTS-TMS interactions |
| Train integrity | Currently long detection times for loss of train integrity | Novel solutions required to provide sufficiently low train integrity loss detection times |
| Train operation: MO, ATP and ATO | Slow reaction times in manual operation | Sufficient safety margins, operation in ATO mode where available |
| Interaction of ATO and ATP with VCTS undefined | Definition of VCTS interaction, software-based implementation | |
| Increasing complexity of on-board traction/brake control interfaces | Utilization of available interfaces or development of novel VCTS interface | |
| Train positioning | Current technology not accurate enough | Development of high accuracy train positioning solutions complemented by suitable redundant distance measuring |