Braking systems
The braking system decelerates a rail vehicle by converting kinetic energy into heat or electrical energy, and must maintain stopping performance under all track and load conditions within defined safety margins.
European rolling stock uses three primary braking modes, often combined in a blended control strategy. Friction braking acts directly on rotating elements — wheels or axle-mounted discs — through pads or blocks. Regenerative braking converts traction motor kinetic energy back to electricity during deceleration, returning it to the supply system or dissipating it in resistors.
Magnetic track brakes apply a direct electromagnetic force to the rail surface, independent of wheel–rail adhesion, and are used as supplementary emergency braking at high speed or on tram networks where adhesion is unreliable.
Each mode has an adhesion dependency profile: friction and regenerative braking depend on wheel–rail friction; magnetic track braking does not.
Air brake system
The automatic air brake, standardised under UIC 540, operates on the fail-safe principle: a continuous 5 bar pressure in the brake pipe holds brakes off; any reduction in pipe pressure — whether commanded or caused by a pipe break — applies the brakes across the train.
Each vehicle carries a distributor valve responding to pipe pressure, a reservoir, and brake cylinders. The system allows trains of several hundred metres to operate with consistent brake behaviour across all vehicles without electronic interconnection.
Electronic braking control systems layer on top of the pneumatic foundation in modern stock, enabling variable brake force distribution, blending between friction and regenerative modes, and integration with ETCS brake curve calculations.
Friction braking
Disc brakes are standard on mainline passenger stock above approximately 160 km/h, as tread blocks produce unacceptable polygonalisation and noise at high speed. Brake discs are produced from alloyed grey cast iron or steel; pad materials are sintered metal or organic composite selected for thermal capacity, noise, and wear rate.
Block brakes on cast-iron shoes remain in service on freight wagons and some regional stock, where their simplicity and low cost outweigh the profile-preservation advantage of disc braking.
Wheel slide protection
Wheel slide protection (WSP) is mandatory on all new rolling stock under EN 15595. WSP monitors individual wheelset speed during braking; when a wheel approaches lock-up, it modulates brake pressure to maintain rolling contact and maximise deceleration within adhesion limits.
WSP performance requirements specify minimum stopping distance penalties relative to ideal adhesion across defined contamination scenarios.
Magnetic and eddy current brakes
Magnetic track brakes are standard on trams and some regional diesel multiple units, and are required by infrastructure managers on certain lines as a condition of high-speed operation.
Eddy current brakes, which generate retarding force through electromagnetic induction in the rail without contact, are used on high-speed platforms where minimal wear is required; their use is restricted on some networks due to stray current and ballast heating effects. Brake force calculations covering all modes are governed by EN 14531.