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A P P E N D I X A

Measurement of Train Pass-by Noise

A.1 MEASUREMENT QUANTITIES

Considering a notional time history of the noise during a train pass-by, shown inFigure A1, several different single number quantities are used to define the noise level.

Maximum level

This is the maximum A-weighted sound pressure level (with the averaging set tofast) over the pass-by, LAmax.

Commonly, the term maximum level is also used to refer to the average level ofthe plateau region during a pass-by. This is more useful than the actual maximum

level, which can be influenced by a single noisy wheel, but is less well defined.

SEL (sound exposure level)

The SEL is formed from the integral of the squared pressure over the whole pass-by (including the rising and falling parts), normalized to 1 second:

SEL 10log10

t2t1

p2t

p2refdt

(A1)

time

S

ound

pressure

level,dB

Tp

Lmax Leq,Tp

Leq,T20 dB

SEL

1 s

FIGURE A1 Notional time history of train pass-by noise indicating various quantities

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where p(t) is the pressure at time t, pref is the reference pressure and the times t1 andt2 are chosen to include the whole pass-by, or more practically they are usuallydefined as the points at which the level is 10 or 20 dB below the maximum level, asshown in Figure A1. As the passage time is usually longer than 1 s this will give a level

that is higher than the maximum level. The SEL can readily be used as input toa calculation of long-term noise exposure based on equivalent sound levels, LAeq.

Short-term equivalent levels

The short-term equivalent levels, LAeq,Tare defined in a similar way to long-termLeq values. These have the form

LAeq;T 10log101

T

t2

t1

p2t

p

2

ref

dt (A2)

where T t2 t1. The duration Tmay be chosen to represent the length of a vehicleor of the whole train (Tp, the length of the train over buffers, divided by its speed) orit may be the time between points at which the level is 10 or 20 dB below themaximum level.

For a train of similar vehicles, LAeq,Tp, the equivalent pass-by level, is a moreformalized means of measuring the average level during the pass-by. However, itdoes not take account of the rising and falling parts of the measurement and so itdoes not include the whole energy of the train pass-by. This makes it less suitablefor calculating long-term Leq values. On the other hand, the equivalent level overthe 10 or 20 dB points takes account of the whole pass-by but presents a levelthat is lower than the LAeq,Tp and which is sensitive to the duration included inthe average.

TEL (transit exposure level)

The TEL is formed from the same integral as the SEL, i.e. over the whole pass-by,but is normalized by the passage time Tp rather than the measurement time:

TEL 10log10

1

Tp

t2t1

p2t

p2refdt

(A3)

Since Tp< t2 t1, again the TEL may be greater than the maximum level. The TELresults measured for various high speed trains [A1] were found to be between 0.5 and1.5 dB higher than the corresponding LAeq,Tp results.

A.2 MEASUREMENT PROCEDURES

ISO 3095-1975

Since 1975, ISO 3095 provided a standard method of measuring train pass-bynoise [A2]. This was based on a measurement location at 25 m from the centre of the

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track. The measurement quantity was the maximum A-weighted sound pressurelevel (with the averaging set to fast) over the pass-by, LAmax.

The principal difficulties with ISO 3095-1975 were that the track condition wasnot defined other than that it should be in good condition. Large variations can be

found for a given vehicle depending on the test location.

ISO 3095:2005

A modified standard was under development for a considerable time and wasfinally approved in 2005, ISO 3095:2005 [A3]. This includes a limit on the railroughness and definition of the track in terms of decay rates. These are intended toensure that the measurement is influenced as little as possible by the track, andmainly determined by the properties of the vehicle (both its roughness and its vibro-acoustic properties). The noise level is defined in terms of the TEL for the whole train

or the LAeq,Tp for parts of the train.

TSI High Speed Trains 2002

The Technical Specifications for Interoperability (TSI) were produced for theEuropean Union following Directives and include requirements for noise levels.These define their own measurement procedure and also set limit values fortrains. The TSI for High Speed Trains [A4] came into effect in 2002. It includesa limit curve for roughness which is more strict than that in ISO 3095:2005. Thetrack was defined in terms of its type of rails, sleepers and pad stiffness. The noiselevel is defined in terms of the TEL for the whole train or the LAeq,Tp for parts ofthe train, as in ISO 3095:2005. However, the TSI-HS is undergoing revision andthese requirements are likely to change to bring them into line with the TSI forConventional Rail.

TSI Conventional Rail 2004

The TSI for railway vehicles intended to operate at conventional speeds (up to190 km/h) was introduced subsequent to that for high speed trains [A5]. Conse-quently, the measurement procedure defined was updated. The track specification,referred to as ATSI, includes a different rail roughness specification and the track wasdefined in terms of its decay rate rather than the pad stiffness. The measurementquantity is now LAeq,Tp for the whole train as well as individual vehicles or parts ofthe train.

A.3 THE NOEMIE PROJECT

The European NOEMIE test campaign provided trackside noise emission values

of several high speed trains at speeds up to 320 km/h including comparisons ofmeasurements on the same train made in different countries [A1]. Operationaltracks were chosen in five European countries, intended to satisfy the conditions forthe TSIs and were ground to ensure low roughness. The roughness levels of these andseveral other tracks considered are shown in Figure A2 along with the limit values ofISO 3095:2005, TSI-HS and ATSI (TSI-CR).

APPENDIX A Measurement of Train Pass-by Noise 487

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Finally, an alternative limit was proposed referred to as TSI+

which correspondsto the original TSI limit at short wavelengths and the ATSI limit at long wavelengths,which was intended to be more readily achievable. Most of the tracks can be seen tosatisfy this limit in most frequency bands, although the effect of grinding can be seenin some cases at a wavelength of 25 mm. In contrast, the TSI rail roughness limit wasmet in some cases, but the ATSI limit appeared to be too demanding for the existingoperational rail grinding techniques [A1].

In addition, a revised limit for track decay rates was proposed in the TSI+ speci-fications intended to reduce further the potential influence of the track in themeasurements [A1].

REFERENCES

[A1] P. Fodiman and M. Staiger. Improvement of the noise technical specifications for interoperability:

the input of the Noemie project. Journal of Sound and Vibration, 293, 475484, 2006.

[A2] International standard Acoustics Measurements of noise emitted by railbound vehicles,

ISO 30951975.

[A3] International standard Railway applications Acoustics Measurements of noise emitted by

railbound vehicles, ISO 3095:2005.

[A4] Commission decision of 30 May 2002 concerning the technical specification for interoperability

relating to the rolling stock subsystem of the trans-European high-speed rail system referred to in

Article 6(1) of Directive 96/48/EC, reference 2002/735/EC. Official Journal of the European Com-munities, 12, September 2002.

[A5] Directive 2001/16/EC of the European parliament and of the Council of 19 March 2001 on the

interoperability of the trans-European conventional rail system. Official Journal of the European

Communities, 2, April 2001.

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-15

-10

-5

0

5

10

15

20

0.0040.0080.0160.03150.0630.1250.250.5

Wavelength, m

1/3oct

avebandroughnesslevel,d

Bre1m Italy

SpainGermanyGermany (ZW900)France

CR (Toury)Belgium (South)Belgium (North)TSIISO limitATSITSI+

FIGURE A2 Roughness measured at test sites in NOEMIE along with various limit values (from [A1])

488 RAILWAY NOISE AND VIBRATION