ISO/TS 14837-34:2024

Technical
Specification
ISO/TS 14837-34
First edition
Mechanical vibration — Ground-
2024-11
borne noise and vibration arising
from rail systems —
Part 34:
Characterizing irregularity of the
running surfaces with respect to
vibration excitation
Vibrations mécaniques — Vibrations et bruits initiés au sol dus à
des lignes ferroviaires —
Partie 34: Caractérisation des irrégularités de surface de
roulement associées à l'exitation vibratoire
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Characterizing roughness related to vibration excitation . 3
4.1 Roughness and noise or vibration phenomena .3
4.2 Roughness spectrum .3
4.3 Roughness level .3
4.4 Roughness wavelength range .4
4.5 Characterization of roughness .5
5 Principles of measurement and analysis . 5
Annex A (informative) Characterization of localized geometrical features . 8
Annex B (informative) Measuring equipment . 9
Annex C (informative) Processing of roughness profiles in site-specific cases .12
Bibliography .13

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and condition
monitoring, Subcommittee SC 2, Measurement and evaluation of mechanical vibration and shock as applied to
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iv
Introduction
The mechanisms of excitation of ground-borne noise and vibration from railway systems are listed in
ISO 14837-1:2005, 4.2.2, which identifies five excitation mechanisms acting at the wheel-rail interface. These
mechanisms include
a) moving loads (quasistatic) excitation,
b) excitation caused by wheel or rail roughness,
c) parametric excitation,
d) wheel or rail defects, and
e) discontinuities of the track.
This document is concerned with excitation by roughness. The aim of this document is to
f) define the term roughness used in connection with the source of ground vibration from railways,
g) provide guidance regarding the procedures that can be used for roughness excitation measurement and
analysis, and
h) provide guidance regarding the equipment that can be used to measure roughness excitation.
The term acoustic roughness is already defined by common use and in EN 15610. The mechanism by which
acoustic roughness generates vibration, leading to noise in the range f = 50 Hz to f = 6 kHz, is essentially
the same as that which is a source of ground vibration in the frequency ranges of approximately f = 1 Hz to
f = 80 Hz and approximately f = 20 Hz to f = 250 Hz, that leads to ground-borne or structure-borne noise.
This document therefore draws upon the established definitions, methods of measurement and methods
of analysis for acoustic roughness to provide guidance for the measurement and analysis of the roughness
pertaining to ground-borne vibration and ground-borne noise.

v
Technical Specification ISO/TS 14837-34:2024(en)
Mechanical vibration — Ground-borne noise and vibration
arising from rail systems —
Part 34:
Characterizing irregularity of the running surfaces with
respect to vibration excitation
1 Scope
This document specifies methods for measuring and analysing irregularities of running surfaces for use
in the prediction and assessment of ground-borne noise and vibration arising from railway systems. This
document
a) defines the data that can be described as rail or wheel roughness and that can be used to quantify a
source term for the generation of the dynamic forces that can lead to ground-borne vibration from
railway vehicles,
b) gives guidance regarding the types of equipment that can be used to measure roughness as a variation
of height along the running direction of the rail surface or wheel parameter,
c) gives guidance regarding the methods that can be used to obtain an estimate of the roughness wavelength
spectrum from measurement records taken over a length of rail head or wheel perimeter, and
d) gives guidance regarding the presentation of a roughness spectrum representing the condition of a
length of rail or of a wheel related to its ability to generate vibration.
This document does not
e) give guidance regarding the characterization of localized geometrical features (e.g. switches, crossings,
rail squats, occasional rail joints and localized geometrical defects of the running surface). These features
are likely to produce dynamic forces that are not linear with their amplitude because of the change of
geometry at the wheel-rail contact. Hence these features are not characterized by methods of analysis
defined within this document. Annex A provides further information regarding the characterization of
localized geometrical features,
f) give guidance regarding the specification or testing of roughness measurement equipment that can be
used. Annex B provides an overview of measuring equipment,
g) give guidance regarding the measurement or analysis of track quality for any other purpose than the
assessment of ground-borne vibration,
h) present any example of roughness spectra intended to represent typical roughness. Roughness levels
vary greatly between track sites and any examples used in this document have not been selected on any
other basis than their usefulness for the purpose of demonstrating the principles of analysis,
i) promote any particular make, model or manufacturer of measurement equipment, and
j) recommend or promote software for the implementation of the analysis procedure.
2 Normative references
There are no normative references in this document.

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. For an explanation of
roughness-related terms, see Clause 4.
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
running surface
part of the wheel tread or the rail head, along which the wheel-rail contact passes during rolling
Note 1 to entry: In the case of the rail this is the bright band of the surface of the rail head that contains all the running
positions of the wheel-rail contact.
[SOURCE: EN 15610:2019, 3.9]
3.2
roughness
variation in height of the rail or wheel running surface associated with a particular noise or vibration
phenomenon
3.3
roughness spectrum
amplitude of the roughness expressed as a function of the roughness wavelength λ
[SOURCE: EN 15610:2019, 3.2, modified — “acoustic” has been deleted in the term and the definition.]
3.4
roughness level
L
r
level expressed in decibels, given by the following formula:
r
RMS
L =⋅10 log
r 10
r
where
L is the roughness level in dB;
r
r is the root mean square roughness in μm; and
RMS
r is the reference roughness with r = 1 μm
0 0
Note 1 to entry: This definition applies to values measured either in the form of a roughness wavelength spectrum or
for a specific roughness wavelength band.
[SOURCE: EN 15610:2019, 3.3, modified — “acoustic” has been deleted in the term and the definition and
Note 1 to entry has been replaced.]
3.5
roughness wavelength
λ
ratio expressed in m given by the following formula:
λ=vf/
where
f is the frequency in Hz
v is the train speed in m/s
4 Characterizing roughness related to vibration excitation
4.1 Roughness and noise or vibration phenomena
Roughness is the variation in the height of the rail or wheel running surface. Therefore,
a) acoustic roughness is the roughness associated with the excitation of rolling noise,
b) ground-borne noise roughness is roughness associated with the excitation of ground-borne or structure-
borne noise, and
c) ground-borne vibration roughness is roughness associated with the excitation of low-frequency ground
vibration.
The vehicle-track interaction equation for the excitation of force by vertical profile irregularities in the height
of the rail and/or wheel running surfaces is the same for 4.1 a), b) and c). Only the roughness wavelength
range changes.
4.2 Roughness spectrum
The roughness spectrum is an estimation of the statistical properties of the roughness record over the length
of measurement. A roughness spectrum represents the general geometrical condition of the running surface
and does not represent the geometry of localized features (e.g. a crossing nose, rail joint, dipped joint or
certain kinds of track or rail or wheel defect) that do not occur with sufficient frequency in a measurement
record to be part of its statistical summary of the condition of the track or running surface.
4.3 Roughness level
Figure 1 shows an example of a measured roughness spectrum. It is presented in accordance with the
requirements of EN 15610 but with the roughness wavelength range extended to λ = 4 m to include the
roughness associated with the excitation of low-frequency ground vibration and ground-borne noise. The
presentation is given in logarithmically scaled one-third-octave bands, with the roughness level as a function
of the roughness wavelength, in decreasing order. The default upper limit for a test section specified in
ISO 3095:—, Figure 5 is shown as a reference. This limit is specified to λ = 0,4 m. For the range λ = 0,032 m to
λ = 0,4 m the limit increases at a rate of 20 dB/decade.

Key
X roughness wavelength λ in m, logarithmically scaled
Y roughness level L in dB in one-third octave bands
r
1 measured roughness spectrum
2 ISO 3095:—, Figure 5 upper limit
Figure 1 — Example of a roughness spectrum presented in accordance with the guidance given in
EN 15610
4.4 Roughness wavelength range
Table 1 illustrates the relationship between roughness wavelength, train speed and the resulting excitation
frequency. The shaded cells indicate the range of roughness wavelengths defined as acoustic roughness
in EN 15610. Roughness wavelengths that lead to low-frequency ground-borne vibration (approximately
f = 1 Hz to f = 80 Hz) or ground-borne and structure-borne noise (approximately f = 20 Hz to f = 250 Hz)
require a roughness definition which includes data to longer roughness wavelengths than for acoustic
roughness.
At short roughness wavelengths (e.g. λ < 1 m), roughness is defined by the wear patterns of the running
surfaces of the wheels and the rails. At long roughness wavelengths (e.g. λ ≥ 1 m) roughness is defined by
the vertical alignment of the track. Long roughness wavelengths are therefore affected by the construction
quality, the construction method and the condition of the track substructure and ballast.

Long roughness wavelengths are not usually relevant for low-frequency ground-borne noise unless the train
is travelling at high speed (e.g. v > 160 km/h in Table 1). Long roughness wavelengths are relevant to low-
frequency ground-borne vibration for all train speeds.
The maximum roughness wavelength for the running surfaces of wheels is limited by the wheel
circumference.
Table 1 — Relationship between excitation frequency, train speed and roughness wavelength
Frequency, f Roughness wavelength, λ, in metres for a given train speed, v
40 km/h 80 km/h 160 km/h 315 km/h
Hz
(11,11 m/s) (22,22 m/s) (44,44 m/s) (87,5 m/s)
1 11,11 22,22 44,44 87,50
2 5,56 11,11 22,22 43,75
4 2,78 5,56 11,11 21,88
8 1,39 2,78 5,56 10,94
16 0,69 1,39 2,78 5,47
31,5 0,35 0,71 1,41 2,78
63 0,18 0,35 0,71 1,39
125 0,09 0,18 0,36 0,70
250 0,04 0,09 0,18 0,35
NOTE Grey shaded cells indicate the wavelength range of “acoustic roughness” as defined in EN 15610.
4.5 Characterization of roughness
Roughness spectra (see Figure 1), summarize the variation in roughness of a running surface with regard to
its roughness wavelength and severity. Localised peaks are apparent, such as those arising from fastening
spacing and from reprofiling operations (e.g. rail grinding). If a limit such as that from ISO 3095:—, Figure 5
is also shown, this demonstrates, for example, that the irregularities shown are of a relatively small
amplitude throughout the roughness wavelength range relevant to both air-borne and ground-borne noise
and vibration (see Table 1).
For some purposes, investigating variations in the measured roughness spectrum from a limit line (such as
the one shown in ISO 3095:—, Figure 5) can be useful. For example the investigation can highlight and give
the correct weight to areas of periodicity throughout the roughness wavelength range of interest.
Spectra (see Figure 1) are not used for rail reprofiling or track maintenance. For these purposes the
roughness wavelength range of interest is divided into intervals that are significantly larger than one-third
octave bands. For example, in EN 13231-2 the ranges of interest are λ = 10 mm to λ = 30 mm, λ = 30 mm to
λ = 100 mm, λ = 100 mm to λ = 300 mm and λ = 300 mm to λ = 1 000 mm whereas in EN 13848-1 the ranges
are λ = 3 m to λ = 25 m, λ = 25 m to λ = 70 m and λ = 70 m to λ = 150 m. Different methods of presenting
the measurements are considered in EN 13231-2 and EN 13848-1 (e.g. peak-to-peak and root-mean-square
(RMS) amplitudes). Measurements undertaken in accordance with the requirements of EN 13231-2 and
EN 13848-1 are appropriate for the purposes which the maintenance is being undertaken and the equipment
that is being used to monitor the work and its quality.
The most detailed presentation of roughness is as measured displacement as a function of distance along
the track. If such a presentation method is used to represent roughness wavelengths pertinent to ISO 3095
as well as roughness wavelengths relevant to ground-borne noise and vibration, the required resolution of
displacement measurements is approximately 0,01 μm.
5 Principles of measurement and analysis
EN 15610 describes the measurement and analysis of acoustic roughness and sets principles of measurement
and analysis that can be applied to roughness associated with the generation of low-frequency ground-borne

vibration and ground-borne noise. EN 15610 should be referred to in order to understand the principles to
be used in the measurement and analysis of acoustic roughness.
EN 15610 defines roughness as a one-third-octave spectrum versus roughness wavelength range from
λ = 3 mm (for different train speeds) to λ = 0,25 m. Acoustic roughness is the origin of rolling noise between
f = 50 Hz and f = 6 kHz. ISO 3095 refers to the requirements in EN 15610 for the measurement and analysis
of roughness and compares the measured spectrum against a limit of up to λ = 0,4 m. The requirements
of EN 15610 were tested before being finalized. This was achieved by having different teams applying
its requirements to two track sections and comparing their test results. The results from both teams are
reported in CEN/TR 15874 which gives further insight into the analysis of roughness data.
Some of the principles of measurement and analysis of acoustic roughness are universal and shall be applied
to measurement and analysis of roughness for ground-borne noise and vibration. Other principles in
EN 15610 are neither necessary nor practical for ground-borne noise and vibration applications.
The universal roughness measurement principles described in EN 15610 include:
a) the ratio of the measured sample record length to the longest roughness wavelength being recorded
should be greater than 60. To obtain a roughness spectrum for λ = 2 m, the sample record should be
a minimum of 120 m for the statistical variance limit to be met. For very long roughness wavelengths
relevant to low frequency ground vibration from high speed trains (e.g. λ > 10 m) it can be difficult to
meet the statistical variance limit due to the long sample record that would be required;
b) the appropriate lateral sample record (number of measurement lines and their spacing across the
running surface) which is dependent on the width of the running surface;
c) the analysis methods that can be used are Fast Fourier Transforms (FFT) and digital filtering. Both
are acceptable for roughness wavelengths associated with ground vibration and ground-borne noise.
However, digital filtering is more appropriate for the sample record lengths that are usually required
for roughness wavelengths relevant to ground-borne noise and vibration; and
d) presentation as one-third-octave roughness spectrum in dB with a reference of 1 µm to characterize the
full sample record (i.e. not including local geometrical features).
Aspects of EN 15610, which are not always necessary for the calculation of ground vibration or ground-
borne noise, include:
— processing to remove pits and spikes from the sample record. These features in the sample record
only affect roughness wavelengths with λ < 50 mm. Hence they are out of the range of interest for low-
frequency ground vibration or ground-borne noise;
— keeping a log of all defects being edited from the record. This is not practical on such long records and
automated removal of defects shall be allowed.
Other requirements for characterizing the irregularity of the running surfaces with respect to vibration
excitation include:
e) any roughness spectrum shall be qualified by the data processing used;
f) reporting of roughness data shall clearly state:
1) the type of measurement device used;
2)
...