Train detection: A snapshot
Modern train detection systems use different approaches. Franz Pointner, Frauscher RAMS Director, analyses various options in terms of their ability to meet current requirements.
Digital possibilities change the concepts of train detection.
What are the core functions of signaling systems? They should guarantee effective traffic management and prevent collisions and derailments. For this, the systems need one thing in particular: information which is as up-to-date and reliable as possible about all trains in the track sections being monitored. Train detection systems are used for this purpose. They confirm the presence of a train and continuously update the details of its position. Train detection systems hereby enable the safe and efficient operation to be maintained and relevant information to be passed on to passengers and other persons, e.g workers on the line.
Based on practical experience, a whole range of requirements can be defined for such systems. This includes for instance meeting the technical prerequisites to be able to detect stationary and moving trains and their integrity in accordance with CENELEC safety standards through to SIL 4. The actual detection speed itself is a key factor, particularly in the vicinity of level crossings. The local accuracy with which trains are precisely detected plays a significant role, for example in railway stations and for shunting operations. The ability to detect and report broken rails is also becoming more important. Automated or intelligent functions that can take over repetitive tasks in particular can guard against human error. Other determining factors include high availability, easy maintenance, an attractive cost structure and minimised risks to personnel.
The system that a railway operator ultimately chooses also always depends on their strategic requirements. After all, in view of the diversity of the different factors, it is very unlikely that a single system can optimally cover all parameters. Instead, each solution will demonstrate particular strengths – even if the aim of all developments is to implement as many of the requirements as possible.
[cf.: Marc Antoni | Director of the Rail System Department, UIC: What will digitization bring for train detection? – Paper at Wheel Detection Forum 2017, pp. 1-2]
State of the art
Based on inductive wheel sensors, axle counters provide reliable and precise data.
Axle counters and track circuits currently represent the state of the art in train detection. Since both approaches are already well-established, a detailed description of their function would be superfluous here. In light of their high availability and due to significantly lower life cycle costs compared with track circuits, axle counters continue to be on the rise throughout the world. They can therefore be regarded as the more sustainable of the two technologies. While both systems are in principle suitable for the fail-safe output of clear/occupied status of a section of track, they only detect the train in restricted track sections and so do not facilitate the continuous tracking of trains.
Trend: Continuous train tracking
It is precisely these continuous train detection systems which are attractive to many railway operators; by enabling a greater train frequency rate, they allow better utilisation of the lines. With this in mind, a whole host of new approaches has already been developed for the recording and transmission of the relevant data. Besides continuous train detection, the aim of these systems is also often to reduce the number of components installed along the lines.
These solutions include the European Train Control System programme (ETCS) and other systems which are based on satellite positioning, trainto-train communication or detection by means of glass-fibre optics, and a combination of these and other technologies.
European Train Control System (ETCS)
European train control system: ETCS Level 1 and 2 combine on-board equipment and trackside installations. The latter shall no longer be required in Level 3.
The ETCS includes three system expansion stages which, owing to long-existing concepts, can also be included in the established train detection methods. They are based on a combination of innovative onboard equipment for trains and the communication of different parts of the operational system via wireless networks.
When ETCS is being used, each railway vehicle needs antennae for radio communication: for the exchange of data with balises or loops and for distance measuring devices, such as odometric systems or Doppler radars. In addition to this, trains are equipped with a separate computer, the European Vital Computer (EVC). It calculates speed profiles, stores train and route data, and controls the operation. The information collected for the train driver is output via a Driver Machine Interface (DMI).
Balises transmit information to passing trains.
Trackside, ETCS systems need balises. These are installed in the track and transmit the data stored on them to passing trains. Two balises are always needed per signal for direction detection. In addition to this, the system needs transmitter masts for GSM-R-based communication with the Radio Block Centre (RBC).
Whilst additional lineside safety systems such as axle counters are used for ETCS Level 1 and 2, the aim of the development of Level 3 is to completely forego the need for corresponding components. Furthermore, the integration of satellite positioning enables virtual balises to be established, which should reduce the number of physical Eurobalises in the track.
Fixed block sections are to be substituted by socalled moving blocks, which allow the seamless control of the distances between trains and thus – at least theoretically – enable travel at an absolute stopping distance. Each train transmits its own position via the RBC and in return receives information about the current position of the train ahead of it, allowing for optimized brake and acceleration control. The distance to the next braking point, the speed and the dynamically calculated speed reduction are displayed via the DMI.
Satellite-based train detection: Trains located by satellite have additional on-board equipment and communicate their current position to the Traffic Control Centre.
A point of criticism which is often cited in conjunction with the ETCS program are the costs for the relevant equipping of trains. In light of the growing demand for cost-effective alternatives for continuous train detection, the EU has also promoted research projects such as SATLOC. This is a train positioning solution based on the Global Navigation Satellite System (GNSS) and public mobile networks, which has been and continues to be specifically developed for lines with simpler operating conditions. In this system, the Radio Block Centre (RBC) and the Control Centre from the ETCS merge with a Traffic Control Centre (TCC).
Rolling stock is located using GNSS, odometers and balises, and transmit the corresponding data to the operation control centre via public mobile networks. Train detection systems and signaling devices with this solution are made largely obsolete. Communication takes place via mobile radio modems with dual-SIM, which allows the use of two networks, thereby providing increased availability.
Successful journeys have already been completed on a test track with good conditions for recording trains via satellite and communication via mobile networks. The system works in compliance with the European Rail Traffic Management System (ERTMS) and supports the necessary ETCS modes and telegrams.
Even the “Train Integrated Safety Satellite System” 3InSat has the aim of reducing trackside components. Using SatNav and SatCom should mean that the majority of physical balises are no longer needed. Instead, a satellite-based train tracking solution should be used which can be integrated into ERTMS systems. These systems should become more affordable, especially on less-frequented lines such as branch lines, regional lines and freight links.
A corresponding presentation by Ansaldo STS at the Wheel Detection Forum 2017 in Vienna gave a hint of how far these approaches have already progressed.
Train-to-train communication via 5G radio networks
Train-to-train communication: Powerful radio networks to 5G standard enable trains to be networked.
5G is a new mobile communication standard which is intended for a new market with new requirements. The objectives are to use higher frequency ranges than 4G and other predecessors, latency times of under 1 millisecond, compatibility with machines and devices and to reduce the energy consumption per bit transmitted.
The principle of closely meshed links should allow individual points in the communication network to be simultaneously connected to several or potentially with all other available points. Highly efficient connections can therefore be established between moving trains. This also enables information about speed, position and acceleration to be passed on to subsequent trains. Another benefit provided are additional options for the moving block approach of ETCS Level 3 mentioned above, for example on highly frequented high-speed lines.
Data relating to possible sources of danger can also be provided effectively. This is obtained via train-to‑X‑communication – i.e. communication between trains and any objects – and transmitted directly, allowing journey characteristics and operation as a whole to be significantly optimised.
The greatest challenges when introducing 5G is the increased data throughput, reduced latency and – particularly crucial to the railway sector – maximum availability and safety.
Glass-fibre optics: Using systems based on glass-fibre optics for train detection reduces the retrofitting costs for trains to a minimum.
Unlike the solutions described above, which are geared towards a reduction in trackside components, systems based on glass-fibre optics focus on minimizing retrofitting costs on trains. Origin, design and a technical inventory of the rolling stock are insignificant when it comes to detection, since this is exclusively realized across fibre optic cables along the track. For this, only a single fibre of these cables has to be charged with laser pulses. The light of the pulses is reflected at a number of points within the glass-fibre and the reflections are captured at the transmitting unit.
If vibration or sound waves hit the fibres, the reflected light only changes slightly. This produces a signature which can be evaluated with the relevant algorithms and assigned to specific events at a specific location. A variety of information can be deduced from the possible recordings from rolling stock along a monitored section of track. The number of systems and components needed for continuous train detection can hereby be reduced to a minimum, whilst operational efficiency and interoperability are increased significantly.
Each of the approaches described here has the potential – as a stand-alone solution or in combination with other technologies – to increase the train frequency rate on certain lines. Depending on the characteristics and costs, the individual concepts are suitable for use in different segments, such as freight routes, highly frequented lines, or branch lines with little traffic.
On the outskirts of sensitive areas especially, such as at level crossings or in railway stations where several sections of track run directly side by side, various points still need to be clarified for the options described here. This applies in particular to applicable standards concerning safety. The requirements regarding redundancy, precision and availability must also be met. There are therefore still many challenges when it comes to developing new train detection systems.
Progress is already clearly noticeable, not least because of the increasing digitisation of the railway sector. New impetus can also be found outside of the railway industry, e.g. from new ways to record – and in particular transmit – data.
Operators and system integrators shall face major challenges in future in light of this dynamic and the diversity of the topic. They will have to come to grips with the strengths and weaknesses of individual solutions (or in the case of the ETCS, its expansion stages) and balance the conflicting priorities of safety criteria and cost-effectiveness. They can therefore decide which approach is the best one for them, depending on the individual requirements, actual or planned train frequencies, condition and status of the track infrastructure, geographical conditions and other criteria.
Close collaboration between component manufacturers, system integrators and railway operators shall therefore be more important in the future than ever before. Only then can the complex challenges in the triangle of technical possibilities, normative requirements and individual parameters be met.
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