A railway coupling is the mechanical interface between adjacent vehicles in a train, transmitting longitudinal traction and braking forces, while side buffers on the legacy system carry the compressive forces and maintain a defined separation under all operating conditions.
Two coupling systems operate in parallel across the European network: the manual screw coupling with side buffers, and the automatic coupler.
The divide runs through vehicle design as much as operations — and on the freight side, the coupling is one of the few rolling stock components now targeted for fleet-wide replacement.
Screw coupling and buffers
The screw coupling with side buffers, standardised under UIC leaflet 520 (draw gear), is the legacy system used on mainline passenger coaches and the majority of freight wagons. It requires manual attachment by a shunter and provides no automatic electrical or pneumatic connection.
Tensile force passes through a threaded link and hook; compressive forces are carried by side buffers on each vehicle end.
For new-build vehicles, buffer characteristics are specified in EN 15551 and draw gear in EN 15566, both referenced by the TSI for freight wagons; UIC 526-1/2/3 cover the legacy buffer strokes of 105, 75 and 130 mm respectively. Buffer head diameter and height tolerances define compatibility across the legacy fleet.
The system is mature and in widespread use, but it imposes a hard operational constraint: trains cannot be combined or split without manual intervention, and no electrical signals pass between vehicles.
Automatic couplers
Automatic couplers using the Scharfenberg “Type 10” interface, defined mechanically and pneumatically under EN 16019, are standard on metros, trams, and electric multiple units across Europe. EN 16019 covers the mechanical and pneumatic connection; electrical connectors are added to the same interface but sit outside the standard’s scope.
Dellner is one of the manufacturers supplying couplers to this interface, alongside Scharfenberg itself.
Scharfenberg couplers align, engage, and lock automatically when two vehicle ends are brought together at low speed. The coupling head contains the mechanical connection, brake pipe and main reservoir connections, and multi-pin electrical connectors.
Dellner-built couplers to the same interface are common on high-speed and inter-city stock, with tensile strength ratings that vary by product variant rather than by manufacturer.
Both types allow rapid coupling and uncoupling from the cab, supporting multiple-unit working and station reversal without crew involvement.
The Digital Automatic Coupling programme
The Digital Automatic Coupling (DAC) programme aims to replace screw couplings across the freight wagon fleet with automatic couplers incorporating data and power connections.
DAC enables continuous train integrity monitoring, remote brake testing, and condition data transmission from each wagon — prerequisites for longer and faster freight trains and for automatic train operation (ATO) in freight.
The EU has co-funded DAC development and deployment studies through CEF and Horizon Europe, including DAC4EU, which completed technical validation in June 2026.
A mainline freight rollout by 2030 was the original EDDP framing; EU-Rail’s current partnership model runs investment from 2028 to 2034, with a second development phase set for 2027–2028, and industry sources now describe rollout extending into the 2030s rather than fitment complete by 2030.
Industry estimates put the wagon fleet requiring retrofit at several hundred thousand units across Europe; the precise figure varies by source and is not yet fixed by a binding EU register.