ISO/TR 8955:2025
(Main)Railway infrastructure — Track quality evaluation — Chord-based method
Railway infrastructure — Track quality evaluation — Chord-based method
This document describes the relationship between an inertial measurement system and a chord measurement system applying the chord-based method with different chord length and chord division. This document is applicable to 1 435 mm and wider track gauges. This document does not apply to urban/light rail systems, tramways and any track gauge narrower than 1 435 mm.
Applications ferroviaires — Qualité géométrique de la voie — Méthode sur la base du cordeau
General Information
Standards Content (Sample)
Technical
Report
ISO/TR 8955
First edition
Railway infrastructure — Track
2025-03
quality evaluation — Chord-
based method
Applications ferroviaires — Qualité géométrique de la voie —
Méthode sur la base du cordeau
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 2
5 Relationship of measuring systems and evaluation methods for longitudinal level and
alignment . 3
5.1 Measuring systems .3
5.2 Evaluation methods .4
5.3 Relationship of measuring systems and evaluation methods .4
6 Chord measurement system and chord-based method of longitudinal level and
alignment . 5
6.1 Chord measurement system . .5
6.1.1 General .5
6.1.2 Symmetrical chord method .5
6.1.3 Asymmetrical chord method .5
6.2 Transfer function .6
6.2.1 General .6
6.2.2 Ratio of the chord division .7
6.2.3 Chord length .10
6.3 Chord based method and chord length class .10
6.3.1 Chord based method .10
6.3.2 Chord length class .11
7 Colouring process .11
7.1 Definition of colouring process .11
7.2 Colouring method . 12
7.2.1 Digital filtering by FIR (finite impulse response) . 12
7.2.2 Digital filtering by IIR (infinite impulse response) .14
7.2.3 Space domain method .14
7.2.4 Frequency domain method .14
7.3 Verification of colouring process . 15
7.3.1 Introduction . 15
7.3.2 Verification with test signals .16
7.3.3 Verification with recorded track geometry data .17
8 Recolouring process .18
8.1 Definition of recolouring process .18
8.2 Recolouring method . 20
8.3 Verification of recolouring process . 20
9 Elimination of influence of track geometry layout.20
10 Usage of restored waveform .21
Annex A (informative) Example of colouring method in MATLAB language .22
Annex B (informative) Verification of colouring/decolouring .30
Bibliography .43
iii
Foreword
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iv
Introduction
ISO 23054-1 describes the wavelength range method and the chord-based method in parallel as methods
for evaluating track geometry quality. ISO 23054-1 specifies a detailed technique for obtaining the track
geometry in a desired wavelength range from the signal measured by an inertial measurement system
or the chord measurement system. ISO 23054-1 does not specify a technique for obtaining the signal by a
particular chord-based method from the signal measured by an inertial measurement system or a chord
measurement system with a different chord base.
The chord-based method is a method of managing the track geometry using an evaluation signal that
emphasizes the track geometry of a specific wavelength component, and is a method used in many countries.
The chord measurement system and the chord-based method are used to measure and evaluate the track
geometry parameters: alignment and longitudinal level.
This document provides information on the chord-based method for track geometry evaluation, looking
specifically at the relationship between an inertial measurement system and a chord measurement system
applying the chord-based method with different chord length and chord division. This document is intended
to be used in conjunction with ISO 23054-1.
v
Technical Report ISO/TR 8955:2025(en)
Railway infrastructure — Track quality evaluation — Chord-
based method
1 Scope
This document describes the relationship between an inertial measurement system and a chord
measurement system applying the chord-based method with different chord length and chord division.
This document is applicable to 1 435 mm and wider track gauges. This document does not apply to urban/
light rail systems, tramways and any track gauge narrower than 1 435 mm.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 23054-1, Railway applications — Track geometry quality — Part 1: Characterization of track geometry and
track geometry quality
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 23054-1 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
wavelength range method
evaluati
...
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