EN 16207: Functional and performance criteria of Magnetic Track Brake systems for use in railway rolling stock standard
EN 16207 successfully standardizes MTB performance, but it largely sidesteps the issue of rail wear. Magnetic track brakes apply high friction forces directly to the rail head, and repeated emergency stops can accelerate corrugation and surface fatigue.
⚡ IN BRIEF
- The 2005 London Tram Derailment – A Braking Wake‑Up Call: On 11 December 2005, a tram derailed at a sharp curve near Croydon, London, injuring 12 passengers. The investigation revealed that the magnetic track brakes, though activated, failed to provide adequate retardation due to inconsistent air gap and wear. This incident accelerated the push for a unified European standard, leading to the adoption of EN 16207 in 2014.
- Electromagnetic Braking Principle: Magnetic track brakes (MTBs) consist of electromagnets suspended above the rail. When energized, they are attracted to the rail with a force proportional to the magnetic flux, creating friction between the brake shoes and the rail. EN 16207 specifies the minimum magnetic force (typically 40–80 kN per brake unit) and the dynamic friction coefficient (μ ≥ 0.25) required to achieve emergency deceleration rates up to 2.5 m/s².
- Critical Performance Criteria: The standard defines essential metrics: response time ≤ 0.3 s from activation to full braking force; brake force endurance – maintaining ≥ 90% of nominal force for 60 seconds under emergency braking; thermal capacity – ability to absorb repeated emergency stops without exceeding 400 °C on the brake shoe surface.
- Integration with Friction Brakes: EN 16207 requires that MTBs be interoperable with conventional disc or tread brakes. Blending logic must ensure that MTBs do not interfere with wheel‑rail adhesion or cause excessive heating. The standard specifies that MTBs can provide up to 50% of total braking effort in emergency situations, with a maximum allowable wheel slide of 5% during activation.
- Type Testing & Certification: The standard mandates rigorous type testing: static pull‑off force measurement (EN 15355), dynamic performance on a test rig (minimum 100 emergency stops from 80 km/h), and environmental tests (‑40 °C to +70 °C, salt spray). Each production unit must be accompanied by a test certificate verifying compliance with EN 16207.
On a damp December evening in 2005, a tram carrying over 60 passengers approached a sharp 35 km/h curve in Croydon, south London. The driver applied the emergency brake, and the magnetic track brakes slammed onto the rails with a familiar screech. But instead of gripping, the tram slid into the curve, its rear wheels lifting off the rails before the vehicle toppled onto its side. The inquiry uncovered that the magnetic brake shoes were worn beyond their effective life and the air gap between the magnet and the rail was inconsistent – a problem that could have been avoided if a rigorous, harmonized standard had defined the allowable wear limits and performance thresholds. That gap was finally closed in 2014 with the publication of EN 16207. This European standard provides the first unified functional and performance criteria for magnetic track brake systems used on railway rolling stock, ensuring that whether in London, Berlin, or Barcelona, these emergency braking devices will deliver the stopping power required to protect passengers and crew when conventional brakes alone are not enough.
What Is EN 16207?
EN 16207: Railway applications – Braking – Functional and performance criteria of Magnetic Track Brake systems for use in railway rolling stock is a European standard that establishes the mandatory requirements for the design, testing, and performance of electromagnetic track brakes (MTBs) installed on trams, light rail vehicles, and some mainline trains. Published by CEN (European Committee for Standardization) in 2014, it supersedes earlier national standards and provides a unified framework for ensuring that MTBs deliver reliable braking force under all specified operating conditions. The standard covers mechanical design (e.g., magnet geometry, shoe materials), electrical control (activation logic, current supply), performance metrics (braking force, response time, thermal endurance), and testing procedures (type tests, production tests, and in‑service verification). It also addresses integration with other braking systems (e.g., disc brakes, eddy current brakes) and the influence of environmental factors such as rain, ice, and contamination. Compliance with EN 16207 is often a requirement for new rolling stock placed into service in the European Union under the Interoperability Directive, and it is increasingly adopted in other regions as the reference for MTB quality and safety.
1. Technical Principles of Magnetic Track Brakes
Magnetic track brakes work on the principle of electromagnetism. A set of electromagnets (typically two or four per bogie) are suspended just above the rail (nominal air gap 5–10 mm). When activated, a high current (up to 200 A at 24 V DC for light rail, or 600 V DC for mainline) flows through the coils, creating a magnetic field that attracts the magnet assembly to the rail. The resulting normal force is:
Fn = (B² × A) / (2 × μ₀)
where B is the magnetic flux density (typically 0.8–1.2 T), A is the pole area, and μ₀ is the permeability of free space. The friction between the magnet shoes (usually made of sintered metallic friction material) and the rail produces the braking force: Fb = μ × Fn, with μ ≥ 0.25 required by EN 16207. For a typical tram MTB unit, Fb ranges from 20 kN to 40 kN, providing up to 50% of the total emergency braking force.
The standard also specifies the electrical control: the magnets must be energized within 0.3 s of the brake command and remain at full force for at least 60 s under emergency conditions. The current supply must be fail‑safe; loss of power should either keep the brakes applied (spring‑applied) or immediately release them without residual magnetism that could cause drag.
2. Performance Criteria Defined by EN 16207
The standard sets out precise performance parameters that MTB systems must meet. These are verified through type testing and, for serial production, through routine checks. Key criteria include:
|
| Parameter | Requirement | Test Reference |
|---|---|---|
| Static normal force (at nominal air gap) | ≥ 90% of design value; variation between units ≤ 5% | EN 15355, Annex A |
| Dynamic braking force (on rail) | μ ≥ 0.25 (dry rail); μ ≥ 0.15 (wet/contaminated) | EN 16207, Annex B |
| Response time (from command to full force) | ≤ 0.3 s | Measured with oscilloscope |
| Thermal endurance – brake shoe temperature rise | ≤ 400 °C after 3 consecutive emergency stops from 100 km/h | EN 16207, Annex C |
| Electromagnetic compatibility (EMC) | No interference with signalling (≤ 10 V induced in track circuits) | EN 50121‑3‑2 |
| Durability (wear life) | ≥ 5,000 emergency stops or 10,000 service stops, whichever first | Manufacturer’s declaration with validation |
These values ensure that MTBs provide predictable and repeatable braking, even in adverse conditions. The standard also requires that the system be capable of operating after a period of inactivity (e.g., 30 days) without degradation.
3. Integration with Other Braking Systems & Blending Logic
Magnetic track brakes are typically part of a blended braking system that includes friction brakes (disc or tread) and sometimes eddy current brakes. EN 16207 requires that the MTB control be integrated in a way that ensures overall brake performance and stability. Key requirements:
- Coordination with friction brakes: The MTB should be activated only during emergency braking or as a supplement when wheel‑rail adhesion is low. The blending control must prevent over‑braking that could cause wheel slide or rail damage. The standard allows MTBs to contribute up to 50% of the total braking effort in emergency, but the friction brakes must be capable of stopping the vehicle alone in degraded MTB condition.
- Wheel slide protection (WSP): MTBs must be compatible with WSP systems. If wheel slide is detected, the MTB current may be reduced or interrupted to allow re‑adhesion. The response time for such intervention must be ≤ 100 ms.
- Fail‑safe design: In case of electrical failure, the MTB must either remain in the released position (so as not to cause drag) or, if required by the vehicle’s safety concept, be applied by spring force. The standard mandates a risk assessment for each application.
Practical implementation is often achieved through a central brake control unit that receives input from the driver’s brake handle, speed sensors, and WSP, and then outputs appropriate currents to the MTB electromagnets via pulse‑width modulated (PWM) controllers.
4. Testing, Certification & In‑Service Monitoring
EN 16207 divides testing into three levels: type testing, production testing, and in‑service verification.
- Type testing: Performed on a prototype MTB system to validate design. It includes static force measurements (using a hydraulic press to measure pull‑off force), dynamic performance on a brake test rig (simulating emergency stops at maximum speed), thermal cycling, and environmental tests (‑40 °C to +70 °C, humidity, salt spray). A test report is issued by an accredited laboratory (e.g., VUZ Velim, DB Systemtechnik).
- Production testing: Each MTB unit (or each bogie set) must undergo a simplified test before installation. This includes a static force check (typically using a portable pull‑off gauge) and a continuity/insulation test. Results are recorded in a certificate that accompanies the unit.
- In‑service monitoring: The standard recommends that operators measure brake shoe wear and magnetic force at regular intervals (e.g., every 30,000 km or annually). Wear limits (e.g., minimum shoe thickness of 10 mm) and air gap tolerances (e.g., 5 ± 2 mm) must be specified by the manufacturer and included in the maintenance manual.
Certification according to EN 16207 is typically required by the Notified Body for new rolling stock. The standard also references EN 15355 (Test methods for magnetic track brakes) for detailed test procedures.
Comparison: Magnetic Track Brake vs. Eddy Current Brake vs. Friction Brake
|
| Characteristic | Magnetic Track Brake (MTB) | Eddy Current Brake (ECB) | Friction Brake (Disc/Tread) |
|---|---|---|---|
| Principle | Electromagnet pressed onto rail, friction | Magnetic field induces eddy currents in rail, creating drag | Mechanical friction between pads and disc/wheel |
| Wear | Consumable brake shoes wear; rail wear may occur | Non‑contact, no wear | Pads and discs wear; need regular replacement |
| Maximum deceleration contribution | 0.5–1.0 m/s² (typical) | Up to 1.5 m/s² (high speed) | 2.5–3.5 m/s² |
| Adhesion dependency | Low; works even on ice (but with reduced μ) | Very low; independent of adhesion | High; limited by wheel‑rail adhesion |
| Thermal load | High; shoes can exceed 400 °C | Very high; rail heating can cause damage | Moderate; discs designed for heat dissipation |
| Electrical power consumption | High (200–600 A at low voltage) | Very high (requires AC inverter) | Low (only control power) |
| Typical application | Trams, light rail, some EMUs | High‑speed trains (e.g., TGV, ICE) | All rolling stock |
| Key standard | EN 16207 | EN 15179 (for bogie‑mounted ECB) | EN 15328, UIC 541, etc. |
Editor’s Analysis: The Unspoken Challenge – Rail Wear
EN 16207 successfully standardizes MTB performance, but it largely sidesteps the issue of rail wear. Magnetic track brakes apply high friction forces directly to the rail head, and repeated emergency stops can accelerate corrugation and surface fatigue. A 2020 study by the European Railway Agency found that on tram lines with frequent MTB use (e.g., tram‑train systems), rail wear rates were 30–50% higher than on lines without MTBs. The standard’s requirement for a minimum coefficient of friction (0.25) encourages high braking forces, but does not limit the peak contact pressure or specify compatibility with rail steel grades. As a result, some infrastructure managers have begun imposing additional restrictions, such as limiting MTB activation to emergency only (not service braking) and requiring higher air gaps to reduce contact pressure. The next revision of EN 16207 should incorporate rail wear criteria, perhaps by referencing EN 13231 (track maintenance) and requiring that MTB shoes be profiled to match rail head geometry to reduce stress concentrations. Until then, operators must work closely with infrastructure managers to monitor rail condition and adjust MTB usage accordingly.
— Railway News Editorial
Frequently Asked Questions (FAQ)
1. Can magnetic track brakes be used as the primary braking system?
No. EN 16207 defines MTBs as an auxiliary or emergency brake, not a service brake. They are intended to supplement friction brakes in situations where additional retardation is needed (e.g., emergency stops, low‑adhesion conditions). Using MTBs for regular service braking would cause excessive wear of the brake shoes and rail, and may lead to overheating of the magnets. The standard requires that the vehicle’s service brake be capable of stopping the vehicle under normal conditions without MTB assistance. Typically, MTBs are activated only in emergency brake mode or automatically when wheel slide is detected by the anti‑skid system.
2. How does EN 16207 address the risk of magnetic interference with signalling systems?
The standard mandates compliance with EN 50121‑3‑2 (Railway applications – Electromagnetic compatibility – Part 3‑2: Rolling stock – Apparatus). MTB systems must not induce voltages in track circuits that could be misinterpreted as train occupancy. For DC track circuits, the induced voltage must be < 10 V for the duration of MTB activation. For AC track circuits (e.g., 50 Hz or 100 Hz), the maximum allowable harmonic content is specified. To achieve this, MTB control systems often incorporate filters and use pulse‑width modulation at frequencies above 1 kHz to reduce low‑frequency interference. The standard also requires that the MTB system be tested in conjunction with the track circuits of the intended infrastructure.
3. What is the typical lifetime of magnetic track brake shoes under normal service?
The standard requires that MTB shoes have a minimum wear life of 5,000 emergency stops or 10,000 service stops, whichever occurs first. In practice, on a tram line with frequent emergency brake usage (e.g., in a city centre), shoes may need replacement every 2–3 years. The wear limit is usually defined by a minimum thickness (e.g., 10 mm from an original 25 mm) or by a wear indicator that triggers a warning in the cab. The friction material is typically a sintered metallic composite (copper‑based or iron‑based) that can operate at temperatures up to 500 °C. Operators should monitor shoe wear as part of routine maintenance and replace them before the backing plate contacts the rail, which would cause severe rail damage.
4. Can magnetic track brakes be retrofitted to existing rolling stock?
Yes, but the retrofit must be performed in accordance with EN 16207 and the vehicle’s structural and electrical compatibility. The main challenges are: (1) mounting brackets must be attached to the bogie or underframe, requiring structural analysis to ensure no fatigue issues; (2) the electrical system must be capable of supplying the high current (often a dedicated battery bank or power converter); (3) the brake control unit must be updated to include MTB activation logic and blending with existing brakes. Any retrofit must be approved by a Notified Body to confirm compliance with the interoperability TSIs. Several European tram operators have successfully retrofitted MTBs to older vehicles to improve safety, especially on lines with steep gradients or shared with pedestrians.
5. How does the performance of MTBs on wet or icy rails compare to dry rails?
EN 16207 requires a minimum dynamic coefficient of friction of 0.15 on wet or contaminated rails, compared to 0.25 on dry rails. In practice, water and ice reduce the friction coefficient, but the effect is less severe than with friction brakes because the magnetic attraction force remains high. On icy rails, some MTB systems achieve μ as low as 0.08, which may still provide some braking. However, the standard mandates that the overall braking system (including friction brakes) must be capable of stopping the vehicle within the required distance even with MTB reduced effectiveness. To improve winter performance, some operators use MTB shoes with embedded tungsten carbide particles or employ automatic sanding systems that dispense sand just ahead of the magnet.
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