ISO 20138-2:2019

Overview

ISO 20138-2:2019 defines general algorithms for calculating braking performance of railway rolling stock using a step‑by‑step (time‑integration) method. The standard specifies methodologies that use instantaneous input values to compute stopping and slowing distances, deceleration, braking power and energy for vehicles or units. It is applicable across the lifecycle (design, manufacture, testing, verification, investigation) but does not prescribe acceptance criteria, design requirements or methods for wheel‑slide–induced extensions of stopping distance.

Key SEO keywords: ISO 20138-2:2019, railway braking performance, stopping distance, slowing distance, braking power, braking energy, step-by-step calculation, retarding force models, rolling stock.

Key technical topics and requirements

• Step‑by‑step numerical integration: Algorithms are based on time‑stepped integration where braking forces are assumed constant over each time step. Both fixed and adaptive time‑step schemes are considered.
• Instantaneous value inputs: Calculations use instantaneous retarding forces and system states (speed, time, etc.) to compute successive states (distance, speed, deceleration).
• Retarding force models: Mathematical models for brake types (e.g., magnetic track brakes, electrodynamic brakes) and external forces are described; disc and tread brake models are covered in ISO 20138‑1. Time, speed, load and temperature effects can be expressed as dimensionless factors (f(t), f(v), …) and combined multiplicatively.
• Time‑step control and accuracy: Procedures for determining appropriate time steps and equivalent system response time are included to ensure numerical accuracy.
• Supplementary dynamic outputs: Methods to calculate energy dissipated per brake type, instantaneous required wheel/rail adhesion, and maximum braking power.
• Operational considerations: Guidance on input data quality, initial/nominal conditions, wheel diameter, gradients, brake demand levels, degraded modes/conditions and available adhesion.
• Supporting materials: Annexes provide a kinetic calculation workflow, non‑stationary retarding force calculations and worked examples.

Practical applications and users

Who uses ISO 20138‑2:

• Railway vehicle designers and braking system engineers for performance assessment and simulation.
• Test engineers and verification teams to calculate expected stopping distances and braking energy during trials.
• Safety investigators and operators for post‑incident analysis and reconstruction of braking events.
• Standards bodies and consultants for harmonised calculation methods that enable consistent comparisons.

Typical applications:

• Predicting stopping/slowing distances for vehicle acceptance or investigation.
• Quantifying braking power/energy and required adhesion under defined scenarios.
• Comparing results from other braking performance methods and validating simulation tools.

Related standards

• ISO 20138‑1:2018 - complementary part covering mean‑value calculation methods and stationary braking examples; both parts should be considered when calculating stopping and slowing distances.