Advanced Protection System - tomorrow’s safety technology

In addition to the costly construction of new lines, Deutsche Bahn is primarily focusing on running more trains on the existing network. In today's system, however, the maximum number of trains is limited by conventional technology: To guarantee safe train traffic, trains must maintain a safe distance from each other due to their long braking distance. For this purpose, a route is nowadays divided into stationary, physical block sections, which are closed to the following train as long as the preceding train has not yet left them. With the Advanced Protection System (APS), Digitale Schiene Deutschland is therefore working with European partners to develop a train-centric safety technology that breaks away from securing train traffic via fixed blocks and introduces a new type of safety logic. This results in more capacity, more flexible operations and simplified trackside equipment. 


The Advanced Protection System - train-centric safety technology of tomorrow

Paradigm shift in safety technology 

In simple terms, railroad safety technology has two tasks: securing the track and securing the train. The route protection is responsible for ensuring that the train's route is correctly set and secured. In this way, switches are set into the correct position, flank protection is provided to prevent lateral collisions of trains, and journey information is transmitted to the train by signal. This is the task of the interlockings, of which in Germany mainly relay interlockings and electronic interlockings are in use, but also mechanical interlockings, some of which are relics from the imperial era.  

The train control system, in turn, ensures that the train does not exceed specified speed limits and automatically brakes it in the event of deviations, so that hazards are minimized. There are around 20 different train control systems in Europe, three of which are in use in Germany. 


Both trackside protection (interlockings) and train control systems are currently being modernized by Digital Rail Germany with ETCS Level 2 without signals and digital interlockings (DSTW). This already brings a noticeable increase in capacity and efficiency into the railway system and creates a uniform technical basis, although it requires a large number of additional field elements such as axle counters. The full potential can only be developed with a safety technology that breaks away from the limiting block logic and introduces a train-centric safety logic. Together with other European Rail Infrastructure Managers, the Advanced Protection System (APS) is being designed as a harmonized and standardized control and safety technology that focuses on the train or the individual train journey. This is a paradigm shift from block-centric to train-centric safety technology. 

The advantages of the Advanced Protection System result from the dissolution of fixed blocks and the introduction of a new type of safety logic

With the introduction of train-centric safety technology, the safety distance between trains is no longer controlled statically via block sections on a line, but via distances before and after the moving train, depending on its speed and braking curve (so-called absolute braking distance). 

Trains can then run in optimal headway (known as "moving block"), allowing more trains to be operated on the same line. For this purpose, new train localization technologies are used which, in contrast to today's localization systems, are no longer installed as field elements in the track bed but are installed on each train. Complex infrastructure, such as trackside train detection systems, which determine the occupancy of blocks by considering the train position, is no longer required and maintenance costs are reduced. The generically designed safety logic no longer has to rely on routes that have been defined once but is capable of always securing a train during its journey from any starting point to any destination. This allows significantly more flexibility in operations management, simplifies operational processes, and enables significantly faster project planning for lines to be equipped. 

 Moving Block increases rail capacity  Moving Block increases rail capacity
Moving Block increases rail capacity

How does the Advanced Protection System (APS) work?

APS can be described as a modern interlocking system which, in contrast to today's Control, Command & Signalling (CCS), combines functionalities of route protection and of the trackside components of train control in a single system. On the train side, APS uses ETCS L3 as the European standard for train control. For APS to do its job, it also needs to work with other systems, just like today's CCS. One important instance is traffic management. During ongoing traffic, disruptions occur from time to time to which the traffic management system must respond. Today, these reactions are carried out manually. In the future, with even denser traffic, this will become increasingly difficult. In parallel with the development of the APS, Digitale Schiene Deutschland is therefore developing the Capacity & Traffic Management System (CTMS), which will use Artificial Intelligence (AI) to manage traffic in the future. The digital ‘brain’ of the rail system determines the optimal timetable and route for each train across every train journey. In the future digital rail system, CTMS communicates its movement permission requests to the APS. APS checks according to the highest safety integrity level (SIL 4) whether routes can be made safe and then transmits the corresponding actuation commands to the track elements and the movement authority (ETCS Movement Authority) to the train. 


APS receives the data basis required for these processes, such as information on topology, infrastructure and vehicle profiles, from the Digital Register (DR) system component. For APS to be able to implement the CTMS request, this data basis must be enriched with current information about the train position and movement. The train must be able to determine its own train position (train front), speed and train integrity (for derivation of the train end) at any time in order to become independent of trackside location systems (f.e. trackside train detection systems) or route markers (f.e. balises) and to place the train at the center of attention. APS receives this information from the train-side systems Train Localization and Train Integrity Monitoring (TIM). This means that the start and end of each train are known and the following train can optimally orient itself to the preceding train. The TIM system is already being implemented in multiple units in the vehicles of the Digital Node Stuttgart. The data is transmitted by radio, either using the conventional GSM-R radio standard or its successor, the Future Railway Mobile Communication System (FRMCS). 

Logical architecture of the Advanced Protection System in interaction with other systems Logical architecture of the Advanced Protection System in interaction with other systems
Logical architecture of the Advanced Protection System in interaction with other systems

The requirements for train and infrastructure equipment are changing 

By moving the train detection functionalities to the train and using moving block logic, the required trackside field equipment is reduced. The amount of balises, axle counters and cable routes is reduced proportionally, which significantly lowers construction and maintenance costs. In addition, signals for communication with the train driver are no longer necessary here either, thanks to the direct connection between interlocking and train as with ETCS L2 without signals. Disturbances of field elements of this kind are one of the main reasons for delays and cancellations in train traffic today.   

Despite the strong focus on the train, the requirements of APS on the on-board equipment are comparatively low: trains must be equipped with ETCS L3, i.e., in addition to the standard equipment with an ETCS onboard unit, another component for determining train integrity is mandatory on the on-board side in order to achieve the maximum possible capacity effects with APS through ‘moving block’. The additional equipment with train localization enables independence from further trackside equipment. The following applies: The more trains are equipped with ETCS L3, the greater the effects.   

The adaptability of the Advanced Protection System facilitates migration to the target image 

Furthermore, APS is downwards compatible. The full potentials are exploited with AI-based traffic management and exclusively with ETCS L3-equipped trains. However, APS is designed in such a way that it can also be connected to a conventional traffic management system or can also secure ETCS L2-equipped trains (without on-board train detection and integrity information) and thus realize hybrid operation. Although APS works without trackside train detection, it can also easily integrate information from balises and axle counters - if available. APS can use GSM-R or FRMCS as radio standard. This high flexibility of APS significantly facilitates migration. 

The Advanced Protection System enables hybrid operation with ETCS L2 and ETCS L3 The Advanced Protection System enables hybrid operation with ETCS L2 and ETCS L3
The Advanced Protection System enables hybrid operation with ETCS L2 and ETCS L3

The Advanced Protection System creates more flexibility through generic and geometric safety logic 

The safety logic of today's interlocking systems is route related. Despite a generic core, each route and its characteristics must be individually planned and elaborately created in the interlocking software, the so-called data preparation. Due to the high safety requirements, the safe implementation of a route must be extensively tested again before it is put into operation. Nowadays, the route is statically determined at the time of planning, changes can only be incorporated afterwards with great effort. In contrast, APS is based on a so-called generic safety logic: The algorithm behind it only needs to be programmed and approved once and can be used on any track without further adjustments. Only the exact track network is recorded (incl. permitted speed, inclination, curve radii). Elements such as track sections or routes are no longer required to be configured at all.  As a common data basis together with systems such as TMS and ATO, the safety logic uses the digital register, thus considerably reducing the data preparation effort for a new line. New routes or route changes (such as the installation of an additional switch connection) only need to be safely included in the Digital Register; no adaptation and re-approval of the APS software is required. 


In addition, the safety logic is designed geometrically, i.e. APS is capable of always securing a train during its journey from any starting point to any destination point and this depending on the current operating situation (e.g. permitted speed depending on available safety buffers). Due to the omission of blocks as safety objects and thus the superfluousness of routes, a geometric consideration of train movements (exclusion of overlaps) is used for front-to-rear collision prevention, front-to-front collision prevention and flank protection. A movement permission only includes the request for a movement from any start point to any destination point of a movement. This movement permission is continuously extended and requested by the Traffic Management System and granted by APS as Movement Authority. Today's security technology does not allow this due to the routes defined statically during data preparation (i.e. pre-planned secured routes that can be used for train operation). APS solves this limiting factor.   

Geometric view of the train movements Geometric view of the train movements
Geometric view of the train movements

The Advanced Protection System simplifies operational processes 

The paradigm shift towards train-centric CCS and the introduction of a generic, geometric safety logic also brings operational benefits. This simplifies operational rules and improves train operation.   


Fewer incidents in rail operations 

APS reduces the number of operational incidents by removing sources of disturbances from the very beginning. Many incidents in today's operations can be traced back to the separation of communication from the interlocking to the track and the interlocking to the train and must be solved manually at great expense. APS dissolves this separation and integrates the instructions for setting the switchable field elements and sending Movement Authorities to the train in one system. As a result, many of the previously described disruptions no longer exist. In addition, less trackside field elements lead to less failures that could disrupt rail operations.   


Less complexity in operations management 

As a general rule, all train movements in the area secured by APS are under full supervision and movement permissions can be granted flexibly. Today, a distinction is made between different operation modes. Thus, in addition to the normal train ride, there is the shunting of trains. Today, such shunting movements are not monitored by a system, but have to be coordinated through complex communication between the dispatcher and the train driver. APS secures all train and shunting movements with the necessary level of safety, thus making manual coordination obsolete as a rule. In addition to increasing safety, this also reduces the workload of operational personnel and enhances train operations. Only in case of malfunction the automatic backup is gradually supplemented by manual backup.   

As described above, APS is no longer dependent on the data preparation of routes due to the geometric safety logic. This significantly increases flexibility in operation management. For example, variable travel paths and overlaps can be used; it is possible to move up to a platform; and tracks can be used in both directions - without any additional data preparation effort. 


The Advanced Protection System solves today's diversity of technologies with a harmonized and standardized European solution from the very beginning  

APS is not a national custom-made product, but a European harmonized uniform platform with few, but sufficient configuration options for national adaptations. Within the framework of RCA (Reference CCS Architecture, an initiative of EUG and EULYNX), a standardized control and safety technology with APS as its core is being redesigned together with other European Infrastructure Managers. Through standardized interfaces, harmonized technology and harmonized operational rules, APS supports the desired European interoperability. The publication of RCA BL1 R0 in September 2022 marks the transition to Europe's Rail System Pillar in which joint standardization by railways and industries will take place. 

RCA is based on the principles of the ERTMS User Group and EULYNX RCA is based on the principles of the ERTMS User Group and EULYNX
RCA is based on the principles of the ERTMS User Group and EULYNX

The Advanced Protection System (APS) fulfills the the mission of Digitale Schiene Deutschland to make the rail system more efficient with a modern control and safety technology. The development and prototyping of APS and other system components has begun. The goal is to have an approved system with the basic functions of APS providing safety for a selected route by the early 2030s. Based on this, APS is to be developed until it is ready for series production and then used as a standard for all new CCS projects.