DAC - The Digital Automatic Coupler
Today the screw coupling is still the standard for freight trains in European countries. Climbing between wagons to hook and un-hook the coupler is a physically demanding manual operation in a hazardous environment. The Digital Automatic Coupler (DAC) is an enabler to create a modern, more efficient, sustainable and competitive European railway freight system that meets the needs of rising transport volumes in a climate protective way.
DAC enables further digitalisation and automation of the European rail system. DAC is considered to revolutionise European rail freight transport by increasing the capacity for shifting freight transport to rail through new technologies and innovations, thus providing a foundation for climate protection and economic growth.
The Digital Automatic Coupling is a prerequisite for an increased railway capacity.
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Automatic (de)coupling/shunting
The basic idea of the couple is to remove time consuming and hazardous labour to begin the journey of making rail freight transportation competitive and more flexible.
Removing the manual labour connected to the shunting of train wagons will also remove the dangerous and heavy process of working between wagons in the shunting yard. A trade of work that today is not very attractive.
Europe is one of the last continents to swap from screw couplers to automatic, something that has been a standard in, for example the United States of America since over 100 years. Attempts to switch the standard coupler in Europe have previously been made but without success.
Contrasting the previously used automatic couplers, the Europeans are attempting to further enhance the technology by including digital connections into the coupler. This is the key in enabling numerous applications which does not make DAC a stand-alone technology but the backbone for “full digital freight train operations” to achieve the ambitious transformation in European rail freight.
Reducing costs and process time
Today’s manual rail freight preparation processes include coupling and de-coupling, connection of air pipes and controlls of brakes, train composition and signals. It requires staff walking up and down the entire train length to do visual and practical inspections, tests and checks that all functions are connected and intact. This manual handling takes a long time which costs money and decreces efficency.
The introduction of the Digital Automatic Coupler allows for, as the name suggests, digital and automatic coupling as well as digital tests of brakes, train composition and signals. The automatization of these processes decreases preparation times which creates more capacity in the terminals. Calculations show that the implementation of DAC, together with the new standard European Rail Traffic Management System, is expected to increase the terminal efficiency by up to 40 % (Lipka, April 2024).
Removing the manual labour connected to the shunting of train wagons will also remove the dangerous and heavy process of working between wagons in the shunting yard.
DAC enables safer braking systems and process reliability
The digital automatic coupler allows the use of an Electro-Pneumatic (EP) braking system which shortens the trains braking distances drastically.
Today’s standard air brake system on freight trains relies on the transmission of air pressure along the brake pipe from the loco back to the last wagon in steps, one wagon at the time. The process takes time which causes the breaking of vehicles to happen at different times along the train. While wagons in the front are breaking, the ones in the back can still push at full speed. When releasing the brakes, the front of the train is pulling the rear, which is still braking, and causes stress to the rails and couplers. This imposes a considerable restraint on operation.
The new EP-braking system will give the train driver instant control over the whole train which greatly improves vehicle reaction time, since it activates the brakes on all wagons at the same time.
Paving the way to intelligent freight trains
With the Digital Automatic Coupler the locomotive’s electronics and energy supply connects through the entire length of the train. Equipped with “electronic intelligence” in the form of control systems, sensors and actuators, the coupler will be capable of acting as the key enabler for many possible future digitization and automation functions required by the rail freight industry.
Communication throughout the train gives the train driver control both during preparation and running time, which both shortens preparation times and gives the driver information to make good decisions while running. Together with sensors in and outside the wagons the driver can for example get alerts if a wheelset stops rotating, which can cause wheel flats, or if a temperate wagon is malfunctioning. Just as the truck today gets information if air is running low in one of the tires, or if the wagon load is uneven, these communication systems are enabled also for rail with DAC.
The full potential of the decided signaling system, European Rail Traffic Management System (ERTMS), is also unleashed with DAC. It gives the train driver and infrastructure manager better information flows to make more informed decisions for driving and for maintenance practices. This will result in more efficient use of the tracks, prevent stops in traffic and help faster and more precise maintenance of both tracks and wagons.
Moving blocks – increasing capacity on the tracks
Together with an electronic train control system of the highest level, the data connections in DAC enable “moving blocks”.
Moving blocks are a signaling block system where the length of a “safe zone” around each train, the blocks, are defined in real time by computers. This requires accurate information of the exact location and speed of all wagons at any given time. It also includes continual communication between the central signaling system and the train's cab signaling system.
Moving blocks allow trains to run closer to each other while maintaining required safety margins, thereby increasing the line's overall capacity.
It may be contrasted with today’s system: fixed block signaling. Fixed blocks are referring to pre-set safety zones where a train is not permitted to enter a section until that section, and most often even the section beyond it, is empty. With low information flows on where the end wagon is located this is effectively enforcing a space between trains of two blocks. The blocks can be a few hundred meters long and up to many kilometers depending on the frequency of trains, speed limits, gradients and so on. The system is built up on lineside signals, a dispatcher or signalman to indicate that the train may proceed or not.
With a better braking system that reacts instantly and simultaneously along with the moving block system, the safety distances could be shortened, and locos could pull heavier and longer trains. This would increase the European railway’s productivity since more rails can be used to drive on. This means that new capacity is released without the need for new infrastructure.
DAC is more than just a coupler. DAC is a key and an enabler for numerous applications. DAC is not a stand-alone technology but the backbone for “full digital freight train operations” to achieve the ambitious transformation in European rail freight. This will allow the DAC to enable even more use cases and to generate a maximal possible benefit.
The illustration shows the different DAC components.
