Overview
ISO 24221:2024 - Railway applications - Braking system - General requirements defines the general principles and lifecycle requirements for brake systems on rail vehicles. Applicable to all rolling stock with metal‑on‑metal wheel/rail contact regardless of speed classification, the standard covers design, safety, verification and operational requirements for the main brake system (service, emergency and stationary/parking brakes). It does not prescribe specific braking performance criteria but establishes the functional, safety and compatibility framework to be used during design and throughout a vehicle’s lifetime.
Key topics and technical requirements
- Scope and applicability
- Applies to all types of rolling stock during design and whole lifetime (metal‑to‑metal wheel/rail contact).
- Does not set stopping‑distance or performance targets.
- Main brake system functions
- Must provide service, emergency and stationary brake application and release.
- Trainwide control devices, brake demand devices, control lines, local controllers, brake units, monitoring and distributed energy storage are core elements.
- Safety and redundancy
- A single failure in the main brake system shall not cause loss of more than 50% of total train braking force.
- Emergency brake function must be automatic; loss of integrity (e.g., unintended separation) must trigger an emergency application.
- Emergency brake control signal propagation speed requirement: ≥ 250 m/s.
- Emergency demands override traction; cancellation does not auto‑release brakes - intentional action required to release.
- Energy and inexhaustibility
- Sufficient on‑board energy (distributed along the train) must be available for at least one emergency stop from maximum speed in any loading up to maximum braking load; local energy must consider Wheel Slide Protection (WSP) consumption under degraded conditions.
- Operational modes and degradations
- Definitions and handling for normal, degraded mode (component failures) and degraded condition (external factors such as low adhesion).
- Includes requirements for brake management / brake blending, additional brakes (independent dynamic/direct brakes), wheel slide protection and adhesion enhancement.
- Design and calculation topics
- Covers verification, testing, thermal capacity, stopping distance extension, duty cycles and service braking calculations (see ISO 20138 references).
Practical applications and users
This standard is essential for:
- Rolling stock designers and OEMs specifying brake architecture and safety redundancy
- Railway operators and fleet engineers managing lifecycle requirements and maintenance strategies
- Systems integrators implementing trainwide brake control, WSP and brake blending
- Certification bodies, safety assessors and regulators assessing compliance and interoperability
- Infrastructure managers and rescue planners verifying compatibility for rescue purposes
Related standards
ISO 24221:2024 provides the high‑level, safety‑focused framework for brake system design and operation; pair it with performance and calculation standards (e.g., ISO 20138) for a complete braking specification and compliance strategy.