ETCS and its implementation have been discussed for a long time. So far, installation on the ground and on-board trains has been limited to ETCS level 2. But for regional lines, ETCS level 3 could be a solution.
It is recalled that ETCS level 2 implies that the driver follows the movement autorisations via a screen on board the train called DMI (Driving Interface Machine), and no longer via the lateral signalling. The speed ranges, slowing down and braking to be carried out appear around the speed dial, and a « target speed » arranged as shown below on the left. It allows the driver to visualise at what point he will have to reach the requested speed or stop.
However, ETCS level 2 still requires operation in sections of 1500 or 2000m or more, in which only one train can be present. ETCS level 2 therefore requires the maintenance of track circuits and axle counters, which are indispensable for train detection, and a large number of kilometres of trackside cables.
The cost issues
A recurring problem in the implementation of ETCS is the need to maintain a transitional period where national signalling systems and ETCS coexist. However, the low-traffic lines are mainly fitted with obsolete national interlockings and traffic management systems (TMS), which are usually expensive to maintain. Railways want to improve performance and safety of regional lines using technological solutions able to reduce life cycle costs.
In Sweden, it took almost seven years to develop, install, test and validate a regional ERTMS, which was built by Bombardier based on Interflo 550 equipment, and was demonstrated in 2012 on the 132 km stretch between the Borlänge railway junction and the small town of Malung on the Västerdalsbanan. Important lessons were learned, including the sometimes-abrupt transition between the Swedish national system and ETCS Level 3, which had to be dealt with.
What was most revealing about the Swedish experience was that the emphasis on intelligent trains rather than intelligent infrastructure instructing trains. This is indicative of a future shift in the basic concept of signalling. The onboard system has been equipped with the normal ERTMS system and was exploited without any changes to the existing system. Compared to normal interlocking and ETCS Level 1 and Level 2, one of the biggest advantages of the regional solution is that the interlocking functions and RBC (Radio Block Centre) are integrated.
This led to the development of new specifications which, at the time, has been designed according to Cenelec norms and fulfils Cenelec SIL 4 requirements with a SIL 3 safety classification.
A few years ago, RFI in Italy started a riskanalysis to draft the ERTMSspecification for regional lines. To reach an ERTMS deployment programme less costly without overlap to legacy systems, the CCSp Regional programme would be the best answer. The « Regional » context refers to secondary lines with medium/low traffic, often single track and electrified or not with « multi-station » operating rules and automatic supervision of the train traffic. ‘Pure’ means the system does not overlap with the national train control and traditional interlocking systems and is based on fixed virtual blocks and virtual track circuits with the option to deploy moving block to increase capacity.
The CCSp Regional system is technically based both ETCS Level 2 combined with multi-station electronic interlockings, with traditional trackside train detection systems (track circuits in the stations and axles counter on the line), and applications based on ETCS levels 2 and 3 with the train integrity function provided by ETCS onboard. This combination of level 2 and level 3 makes it possible to keep track circuits in small stations and to remove them between stations, sometimes over long distances. This means that there is a minimum of equipment to maintain.
Unlike ETCS level 3 on main lines, the ERTMS Regional scheme is not supposed to operate with moving blocks. Instead it uses radio-based interlocking to lower the amount of track-release signalling devices.
Under ETCS Level 3, the trains report their position to the traffic control every 6 sec, using on-board odometry which is reset by balises at intervals, and receive movement authorities in return.
Although ERTMS is designed for moving block, the Regional’ version is specified a ‘virtual fixed block’ application to simplify the changes to its operating rules. Pairs of balises and marker boards are provided at each station, with intermediate balises every 5 km along the line, allowing trains to follow each other through a single line section.
The objective of the italian’s tests with the CCSp Regional system based on ETCS Level 3 without a traditional train detection system was to gain confidence with the operational and technical feasibility of the system, which introduces important innovations in rail traffic management. It also sought to test the switch-over procedures between the existing electromechanical interlocking and axle counters and the new CCSp Regional system. Test were made on the RFI’s 80km Avezzano – Roccasecca line, a non-electrified single-track low traffic line still equipped with an electromechanical interlocking and axle counter treadles.
The RFI “Regional” program includes as a further step too for the introduction of the satellite technology that will allow, through the concept of “virtual balise”, to minimise the number of the physical eurobalises, so substantially contributing to additional decrease of Opex and Capex of the regional signalling system. The measurements acquired in Sardinia within the project ERSAT, developed in collaboration with Ansaldo and the European Space Agency, have shown the maturity of the sat based train localisation approach. The line Pinerolo-Sangone has been already identified as the pilot site where the sat based ERTMS will be put into operation for the first time.
Finally, the adoption of digital radio communication in the rail signalling environment, paired with the removal of the greater part of CCS field devices, means to use 5G and the FRMCS technology under development. While the vision for FRMCS is to be functional without stipulating a particular technology, it is evident that 5G will be its foundational communications technology. Previous technologies such as GSM-R will be migrated to FRMCS. Therefore, the ERTMS L3 Regional system represents a step forward that goes well beyond the digitalisation of rail signalling: it addresses a new way of thinking about railway operations, whilst maintaining the safety standards guaranteed by the most advanced train protection system available on the market, reducing costs and complexity at the same time.
03/10/2021 – By Frédéric de Kemmeter – Railway signalling
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