ISO 2631-4:2001

Overview

ISO 2631-4:2001 is part of the ISO 2631 series on mechanical vibration and shock and gives guidelines for evaluating passenger and crew comfort in fixed-guideway transport systems (rail, light rail, MAGLEV, rubber-tyred metros and tilt-capable vehicles). It explains how to apply ISO 2631-1 (general whole‑body vibration evaluation) to the multi-axis motion environment of fixed‑guideway vehicles, focusing on relative ride comfort (comparisons between systems) rather than absolute comfort limits. The standard covers rectilinear accelerations (x, y, z) and rotational motion about body‑centred axes, and addresses very low‑frequency vertical motions (0.1–0.5 Hz) that can cause kinetosis (motion sickness).

Key topics and technical requirements

• Scope and applicability
  • Applies to people in normal health exposed to translational and rotational vibrations in fixed‑guideway systems.
  • Not intended for high‑amplitude single transients (accidents) or health‑affecting vibration.
• Motion characteristics
  • Describes semi‑random, periodic and quasi‑static motions produced by guideway, vehicle suspension and vehicle dynamics.
  • Notes frequency bands relevant to comfort (e.g., 0.1–2 Hz for curve transitions/roll; 0.5–10 Hz lateral/longitudinal; 0.5–20 Hz vertical).
• Measurement guidance
  • Preference for measurements at the seat/berth‑body interface but allows structural measurements when appropriate.
  • Use a human body‑centred coordinate system or basicentric axes per ISO 2631-1.
  • Measure at vehicle ends and middle (except longitudinal x-axis where one point may suffice); double‑deck vehicles require multiple locations.
  • Roll rate measurement: preferred via a rate gyroscope. Alternatively, roll acceleration (rad/s²) can be approximated by two vertical accelerometers spaced laterally: roll_accel = (a_z_left − a_z_right) / d.
• Analysis
  • Recommends appropriate weighting curves from ISO 2631-1 when evaluating vertical and other axes; highlights differences between weighting curves used in rail practice.
• Test conditions
  • Tests should document track/guideway and suspension condition, wheel wear, vehicle loading (empty and fully laden) and car position/direction.

Applications and who uses it

• Rail vehicle designers and vehicle‑system engineers assessing ride and suspension designs
• Transit agencies and operators specifying passenger comfort requirements
• Guideway/track engineers evaluating alignment, super‑elevation and transitions
• System procurers comparing comfort between vehicles or routes
• Vibration and human factors consultants performing ride comfort assessments and motion sickness analysis

Practical outcomes include better guideway geometry design, improved suspension and tilt strategies, and more informed procurement/specification decisions based on objective motion comparisons.

Related standards

• ISO 2631-1:1997 - General requirements for whole‑body vibration evaluation (normative reference)
• ISO 2631-2 - Vibration in buildings (related series)
• IEC 61260 - Octave‑band and fractional‑octave‑band filters (measurement filtering)

Keywords: ISO 2631-4, whole‑body vibration, fixed‑guideway transport, passenger comfort, rotational motion, ride comfort, kinetosis, rail vibration measurement.