The author would like to thank Talgo for their support in developing this article.
The state of the art in rolling stock has evolved rather quickly in the past few years, and high speed trains are probably the most innovative of all due to the very high service quality, speed and power involved, and complex technological advances such as:
- Advanced three-phase traction motors, usually induction motors, with very high power density and almost maintenance-free, water-cooled traction converters based on semiconductors (IGBT).
- Fully redundant train control and monitoring systems – consisting of highly complex computer networks interconnecting the different vehicles and systems within the train.
- Signaling systems which support the use of Automatic Train Protection as the ERTMS (“European Rail Traffic Management System”), etc.
To illustrate the complexity, train control and monitoring systems are, from the technological point of view, quite similar to those onboard commercial jets – with the obvious differences stemming from the need to control several interconnected vehicles belonging to the same unit.
However, up to now, high-speed services rely on drivers to operate the controls fitted in the driving cab for such purposes.
So the question is: can we expect driverless operation on high-speed trains in the future?
In this analysis we have to consider that in some rail environments, such as automatic metros and people movers, driverless operation has already been achieved successfully.
ERTMS Implementation on the Spanish Infrastructure
ERTMS signaling system was introduced into the Spanish rail infrastructure in order to achieve operations with the maximum levels of safety and reliability.
ERTMS levels 1 and 2 were simultaneously deployed on tracks. The high-speed trains run on level 2, and in case of failure fall back to level 1.
In level 1, traffic management is based on telegrams sent by balises placed on fixed points along the track (figures 2-3). The antennae located under the frame of the unit’s first vehicle receives the data and a computer (EVC – European Vital Computer) processes them (figure 4).
In level 2 such functionality remains operative, however the main bulk of information is exchanged via radio by means of a train-wayside data communication system called “GSM-R,” consisting on a GSM standard specifically intended for its use on railways (figure 5).
Driving modes of AVE trains
Most AVE trains – the Spanish brand for HSR – are fitted with several selectable driving modes. For instance AVE trains of class 102, manufactured by a consortium led by Talgo, are provided with three alternative driving modes: manual, semiautomatic (preset driving speed) and automatic - usually called “automatic train operation” (ATO).
In manual and semiautomatic driving modes, the driver is responsible for choosing the driving speed.
In semiautomatic mode the driver can select a speed and the train will maintain it, applying power or brake depending on the line gradient.
In automatic mode, the driving speed is provided in real time by the ERTMS. This speed is the permitted speed, calculated by the EVC of the ERTMS, working under full supervision mode. Figure 6 shows the ERTMS display (DMI – Driver Machine Interface). The bow indicator is the permitted speed (187.5 mph or 300 km/h in the picture). The needle indicator is the real speed (184.3 mph or 295 km/h in the picture).
Safety is always guaranteed by the ERTMS, which prevents the actual speed from going over the permitted limits regardless of the driving mode being used. The ERTMS system has been designed with the maximum safety integrity level (SIL); for this purpose the value is 4, in compliance with the European standards.
For the purposes of this article, the automatic driving mode (ATO) could be a starting point for implementing an “unattended train operation” (UTO) on high speed trains.
Automatic Train Operation “ATO” Implemented on High-Speed Trains Class 102
This driving mode is intended for an operation where the ATO function is automatically fed, in real time, by the on-board ERTMS, giving the maximum permitted speed.
The driver activates the ATO function by pressing a specific button placed on the driver’s desk (figure 7).
Additionally the driver has the freedom to set the highest allowed speed and the maximum power, by respectively setting the automatic speed control (ASC) handle and the master controller, in the desired positions; it is common to set both controllers (speed and power) to the maximum range value (figures 7-8).
The train control and monitoring system (TCMS) always takes the most restrictive speed value – the lowest one – between the speed values provided by the ERTMS and the ASC handle, and automatically calculates the tractive or braking effort required to respect such speed limit.
Unattended Train Operation (UTO)
Nowadays driverless operation has been successfully introduced in some rail environments such as metros or people movers; similar trends can be observed in other fields such as military aviation (e.g. unmanned aircraft intended for intelligence-gathering).
These experiences, along with the high degree of sophistication already in place in HSR applications, underlines the fact that we already own the required technology for driverless operation on high-speed trains, and it could be implemented provided that some changes be made on both the infrastructure and the rolling stock, as I explain below.
The existing requirements of the ERTMS do not foresee driverless operation, as concrete actions and acknowledgements are required from drivers when the train is running. ERTMS would have to be modified necessarily in order to enable driverless operation under this ATP signaling system.
Stopping at Platforms
ERTMS could bring the train to a halt at platforms by providing a maximum allowed speed of zero at the appropriate time – on a level 2 ERTMS this would be performed over the radio by the corresponding centralized traffic control (CTC). However, as the system stands nowadays, it cannot perform this action with the extremely high accuracy that would be required to stop the train in the exact place unless further changes are carried out.
The automatic metros have solved this problem by placing passive balises in the tracks near the stations, in order to let the train know its exact location as well as the precise place where the train has to stop at platforms.
Currently, the ERTMS uses position balises, but additional balises would be required for driverless operation.
Opening and Closing the Access Doors
An automatic door-unlocking system would be required when the train stopped at the stations, and passengers would then open the doors manually, as is implemented in metros and commuter trains.
The on-board access doors system would need to be informed in some way when the boarding and unboarding process has finished.
This is not easily solved using automatic systems: relying on a preset time for boarding/unboarding is simply not enough, since the associated variability for this operation is too wide in high-speed environments (e.g. very different demands depending on the particular date and time, impact of handling luggage on transfer times, etc.). A time criteria would lead to inefficiency or, even worst, unduly restricting passengers from boarding.
However such automation may not be required at all: the ticket controller could support this function by providing the “train ready to depart” signal when appropriate.
Other Aspects of High-Speed Environments
As mentioned before, high speed environments are dramatically less self-contained and controlled than those of driverless systems. Therefore, there are more factors that could impact operations, and in turn a wider variety of eventualities of a varied nature (e.g., a train stranded at an intermediate point, many miles away from the closest station).
From the rolling-stock point of view, additional redundancy levels should be added to the existing ones in order to boost its reliability. The train architecture should be modified to avoid any “no-go” condition, for both power and control-command systems. Monitoring should be increased to have complete information in a “control center” about the working state of the train. Additionally, the required means to provide remote technical assistance should be provided.
Concerning the infrastructure, similar measures should be taken accordingly to avoid failures and problems.
However, even after taking these measures, there is still a possibility of a train getting stranded because of external causes (e.g. overhead power supply failure, bad weather conditions, obstacles on track, etc.). Additional measures should be provided for early detection and remedy of these events.
Powerful communication capabilities would also be required to keep the passengers continuously and suitably informed – though information displays, intercom systems, CCTV systems, passenger alarms, etc.
The psychological factor on these environments is of paramount importance. Passengers must perceive, through several channels, that the term “unattended” does not apply to them at any rate; on the contrary, they should be clearly informed about what are, for them, the benefits of driverless operation: higher capacity, efficiency and comfortable rides free of human errors.
The Spanish high speed trains feature the highest technology. The automatic train operation (ATO) implemented onboard AVE trains is very close to driverless operation.
From the technology point of view, unattended train operation in high speed environments could be possible in the near future, provided that the required changes are adopted, as pointed out in this article.
However, for the time being, this operation model is not the most ideally suited for typical high-speed environments due to the large number of different scenarios that could arise and their particular nature.
Finally, the possibility of implanting driverless operation should be carefully studied, planned and designed for each specific case, taking into account the hazard log of the whole high-speed system, in order to prevent and avoid risks for passengers.
José A. Jiménez-Redondo, Ph.D is the rolling stock technical director for Renfe – Manufacturing and Maintenance General Directorate.