deliverable d4.1 12m acl

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QCITY issued: 31-01-06

Deliverable D4.1_12M_ACL.doc

DELIVERABLE D 4.1 CONTRACT N° TIP4-CT-2005-516420

PROJECT N° FP6-516420 ACRONYM QCITY

TITLE Quiet City Transport Subproject 4 Noise propagation and receiver perception Work Package

4.1 Quantify influence of screening effects

Description of benefits from various screening techniques

Written by H Malker ACL N Å Nilsson ACL Date of issue of this report 2006-01-31

PROJECT CO-ORDINATOR Acoustic Control ACL SE PARTNERS Accon ACC DE

Akron AKR BE Amec Spie Rail AMEC FR Alfa Products & Technologies APT BE Banverket BAN SE Composite Damping Material CDM BE Havenbedrijf Oostende HOOS BE Frateur de Pourcq FDP BE Goodyear GOOD LU Head Acoustics HAC SE Heijmans Infra HEIJ BE Royal Institute of Technology KTH SE Vlaamse Vervoersmaatschappij DE LIJN LIJN BE Lucchini Sidermeccanica LUC IT NCC Roads NCC SE Stockholm Environmental & Health Administration SEA SE Société des Transports Intercommunaux de Bruxelles STIB BE Netherlands Organisation for Applied Scientific Research TNO NL Trafikkontoret Göteborg TRAF SE Tram SA TRAM GR TT&E Consultants TTE GR University of Cambridge UCAM UK University of Thessaly UTH GR Voestalpine Schienen VAS AU Zbloc Norden ZBN SE Union of European Railway Industries UNIFE BE

PROJECT START DATE February 1, 2005 DURATION 48 months

Project funded by the European Community under the SIXTH FRAMEWORK PROGRAMME PRIORITY 6 Sustainable development, global change & ecosystems

This deliverable has been quality checked and approved by the QCITY Coordinator Nils-Åke Nilsson

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E X E C U T I V E S U M M A R Y This deliverable presents a number of noise reduction tools in the form of new and existing screening techniques. The presented new screening concepts are intended for creating increased propagation attenuation between the noise source and the receiver. Absorbing cylindrical screen top element A full-scale test of absorbing cylindrical screen top elements has been performed north of Stockholm. The new tested screen top element has been supplied with porous sound absorbing material of twin layer type. This means that the sound absorbing material consists of two layers where the outer porous layer has very low flow resistance while the inner layer has a flow resistance that is 2-4 times higher compared to the outer layer. This new design increases the sound reduction due to reduced diffraction and absorption at the screen top edge. The test shows an increased insertion loss due to the screen top elements of 3-5 dB(A).

Acoustic Gallery An Acoustic Gallery is a tunnel-like covering of the entire road just leaving enough openings for ventilation and daylight. In some situations where there are residents close to a road with dense traffic, normal sound reducing measures like screens may not be enough. In order to reach design goals of Lden ≤ 55-60 dB(A) for such cases, it can be advantageous to apply the Acoustic Gallery concept.

Calculations in ray tracing have been performed to investigate the sound reducing performance of the Acoustic Gallery concept. The calculation results show an increased sound reduction of 10-15 dB(A) compared to normal roadside screens.

Train and tram screens - sound absorption for elimination of “climbing” reflexes Because of the “climbing” reflexes between the screen and the train/tram car body, the screen sound absorption has extra effect in the case of train and tram applications compared to e.g. road traffic screens. The effect of efficient absorption on screens for trains and trams has been studied by ray tracing calculations. Calculation results show that for screens at a distance > 3.5 m from the track centre, added absorption results in an increased sound reduction of 5-10 dB(A).

Furthermore it is shown that models NOT including the reflexes between the train car body and screen (common for the prediction models of today e.g. the Nordic Prediction model) will underestimate the sound reducing effect of added absorption. For screens at distances > 3 m from track the underestimation is about 2 dB(A) and for screens at distances < 3 m from track the underestimation can be as much as 6 dB(A). For single sided screens including the effects of the train car body in the model is most important to correctly estimate the effect of added efficient absorption as a sound reduction treatment.

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Lane screens Tyre/road noise is the dominating sound source of today’s road traffic. Tyre/road noise has a very low source height of typically 2-5 cm above the road surface. This low source height opens up new possibilities for using low screens close to the vehicle to create substantial noise reduction.

Lane screens are absorbing low screens located on the lane markings separating lanes. Because the lane screens are located close to the sound source they can achieve a sound reduction comparable with a much higher screen at the roadside. Calculations with CadnaA have been performed to evaluate the sound reducing effect of the Lane screens. The calculation results show that Lane screens of 0.5 m height gives the same sound reduction as 1.8 m high roadside screens.

Prototypes of Lane screens in polyurethane bounded rubber granulate have been manufactured by QCITY Partner CDM in Belgium. Sound measurements on the prototype is planned to be performed in the period 12M – 18M.

Combined noise treatment and crash protection Existing crash protections of concrete or wire fence designs can, for a small extra cost, be redesigned to also work as a noise reduction treatment. This deliverable presents some examples for designs.

Low close-fitting track screens for railways For some years now a new concept on reducing noise from train traffic has been utilized. The concept is to install a low screen only 700 mm high very close to the track, only 1700 mm from the track centreline. One example of a manufacturer of such screens is one of the partners in the QCITY project, Z-BLOC. They have delivered these screens to a large number of installations and the measured insertion loss have been up to 11 dB(A). Due to safety reasons, these close-fitting track screens have only been allowed to be mounted on one side of the track. The two main safety reasons have been:

1. The workers performing track maintenance must have a possibility to escape quickly and safely from the track area.

2. It should be possible to evacuate passengers from a train that has to make an emergency stop between stations

This deliverable presents new designs that are close to resolving these safety questions.

In addition to these close-fitting low screens for trains this deliverable presents new designs adapted for tram traffic. Prototypes of these very low (300-400 mm) close-fitting screens for trams (also called “Platform” screens) have been tested in Athens. The measured insertion loss was 6-8.5 dB(A).

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Medium high transparent reflective noise screens A transparent reflective noise screen of 1.7 m height and placed 3 m from the external rail has been tested in the Athens tram network. The noise screen was especially chosen for its esthetical appearance. The measured average insertion loss was 9-10 dB(A).

In the table below a summary of the investigated screening techniques are presented.

Technique for noise reduction Application

Noise reduction dB(A)

Estimated Cost Euro Comments.

Normal non-absorbing screens

Road and rail traffic 3-15 dB(A)

200 €/m2 height < 3m

300 €/m2 height > 3m

At heights > 3 m the foundations for the screen gets much more complicated which increases the cost.

Absorbing cylindrical screen top elements

Road and rail traffic

3-5 dB (in addition to the existing reduction for sharp edged screen)

200 €/meter The diameter of the cylinder must be at least 500 mm

Acoustic Gallery Road traffic >10 dB(A) increase compared to normal roadside screens

300 €/m2

or typically 5000 €/m

road

Absorption added to normal screens

Tram and train traffic

5-10 dB(A) increase of sound reduction compared to non-absorbing screens

50-100 €/m2 (only the absorbing material)

The screen is assumed to be mounted 4-6 metres from the track centreline. For screens closer than 4 m from the track centreline, the effect can be much higher. This effect is underestimated by normal standard prediction models but can be more correctly predicted e.g. by including the train car body.

Lane screens Road traffic 4-6 dB(A) 650 €/meter (4 lane motorway)

(The combined noise treatment/crash protection can replace the two lane screens closest to the road centerline)

Combined noise treatment and crash protection

Road traffic 1-2 dB(A) as stand-alone measure. by itself

200 €/meter Only the additional porous rubber sheets

Works well as a complement to the lane screens

“Platform screens” (screens, 300-400 mm high, close to track)

Tram lines 6-8.5 dB(A) 200 €/meter

“Platform screens” (screens, 700 mm high, close to track)

Train traffic 6-11 dB(A) 480 €/meter Only one-sided screens are presently allowed

Medium high transparent noise screen


70-75 €/m2 (only the material cost) appr. 140 €/m2 (all costs included)

Can be chosen when the esthetical apperance is important and absorbing screens therefore not possible.

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T A B L E O F C O N T E N T S 1 Objectives and scope of work.............................................................................................. 6 2 Cylindrical, sound absorbing screen top elements........................................................... 7

2.1 The test site for a new type of screen top element ................................................... 7 2.2 Twin Layer technique ...................................................................................................... 7 2.3 Measurement results........................................................................................................ 8

3 Acoustic Galleries.................................................................................................................... 9 3.1 Ray tracing calculations and results........................................................................... 10 3.2 Some basic conclusions based on the ray-tracing calculations. ......................... 12 3.3 Other examples on how the Acoustic Gallery concept could be applied........ 13

4 train and tram screens - sound absorption for elimination of climbing reflexes ........ 15 4.1 Background .................................................................................................................... 15 4.2 “CLIMBING” REFLEXES.................................................................................................... 15 4.3 The sound absorbing material of twin layer type..................................................... 16 4.4 Calculations with aid of ray tracing ........................................................................... 18 4.5 Benefits of railway screen sound absorption compared to estimated cost ....... 27

5 Lane screens .......................................................................................................................... 28 5.1 background to the lane screen concept ................................................................. 28 5.2 Theoretical background............................................................................................... 29 5.3 Design .............................................................................................................................. 31 5.4 Calculations .................................................................................................................... 33 5.5 Benefits compared to estimated cost ....................................................................... 36

6 Combining crash protection and noise treatment ......................................................... 37 6.1 Background. ................................................................................................................... 37 6.2 Supplementing concrete protection devices with sound absorbing rubber granulate designs...................................................................................................................... 37 6.3 Supplementing crash protecting wire fences with sound insulating and sound absorbing rubber granulate designs. .................................................................................... 38

7 Low close fitting track Screens – platform screens......................................................... 40 7.1 Introduction to low close fitting track screens. ......................................................... 40 7.2 Theoretical background............................................................................................... 40 7.3 Low track-screens aimed for train traffic ................................................................... 41

7.3.1 Upgrading the track screen design to meet safety requirements ................ 41 7.3.2 Measured insertion loss of the low close-fitting track screen.......................... 44

7.4 Low close-fitting track screens aimed for tram traffic. ............................................ 47 7.5 Benefits compared to estimated cost ....................................................................... 50

7.5.1 Close fitting track screens for trains..................................................................... 50 7.5.2 Close fitting track screens for trams. ................................................................... 50

8 Medium High Transperent Reflective Noise Screen ........................................................ 51 9 benefits compared to estimated cost for investigated screening techniques ......... 53

Appendix 1 Calculation results on the effect of absorption on screens for trains and trams Appendix 2 Calculation results, Lane screens

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1 O B J E C T I V E S A N D S C O P E O F W O R K The purpose of this delivery is to provide a number of noise reduction tools in form of new screen design concepts. The presented screen concepts are intended for creating increased propagation attenuation between the noise source and the receiver.

The various tools and concepts will be studied and evaluated in connection to the elaboration of Noise Action Plans in urban areas for various noise hot spots in selected sites within the QCITY project. These studies, which will be performed later downstream in the project, will also reveal the applicability and cost effectiveness of each screen design solution reported in this delivery.

Some information regarding the expected costs in comparison to the calculated noise reduction effect is provided in Table 3.

Basic underlying physical principles applied in the presented new designs are e.g.

• Maintaining or increasing the extended propagation path in relation to the unscreened path (i.e. maintaining the Fresnel number) by low screens close to the source (platform screens for trains and trams; lane screens for road vehicles)

• Decreasing diffraction (cylindrical screen top element)

• Introducing sound absorption for elimination of reflections at the source or receiver side. (e.g. mounting sound absorption on the screen inside to avoid “climbing reflexes” between the screen and the train (or tram) car body side)

Each chapter below will describe one separate new screen design solution or a new way to apply already well known physical principles for creating noise reduction by creating excess attenuation in the propagation path between the source and the receiver.

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2 C Y L I N D R I C A L , S O U N D A B S O R B I N G S C R E E N T O P E L E M E N T S

2.1 THE TEST SITE FOR A NEW TYPE OF SCREEN TOP ELEMENT An experimental study has been performed in Stockholm on a new type of cylindrical sound absorbing screen top element. The measurements have been performed with the aim to determine the insertion loss with and without the screen top element. The found insertion loss is caused by reduced diffraction and absorption. Figure 1 below shows the cylindrical screen top elements mounted at the test site in Stockholm.

A separate delivery D 4.2 presents the experimental study more in detail. Below is presented a short summary.

Figure 1. Picture of the test site with cylindrical sound absorbing screen top element mounted onto an already existing (but newly installed) screen project at Täby/Lahäll 15 km northeast of Stockholm.

2.2 TWIN LAYER TECHNIQUE The investigated cylindrical absorbing screen top element has been supplied with porous sound absorbing material of twin layer type (see Figure 1 above). This means that the sound absorbing material consists of two layers where the outer porous layer has very low flow resistance while the inner layer has a flow resistance that is 2-4 times higher compared to the outer layer. By the twin layer technique we ensure that we create an increased refractive characteristic (decreased speed of sound along the depth of the absorbing layer) so that the sound entering the sound absorbing material will be efficiently absorbed. This is desirable since sound transmission along the surface of the absorber should be avoided.

Screen top element

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2.3 MEASUREMENT RESULTS Measurements of the insertion loss with aid of a loudspeaker sound source providing 1/3 octave band filtered noise was performed the night before and after mounting the screen top element. The average insertion loss for the screen top element in each 1/3-octave band is shown in Figure 2 below. The insertion loss in dB(A) when using a typical traffic noise spectrum was found to be about four (3.5-4.5) dB(A). One year after the screen top was mounted, the same measurements were performed, giving about the same results (4.0-5.0 dB(A) reduction). This means that there are no negative environmental long-term effects (from e.g. rain, snow, dust etc.) on the function of the sound absorbing screen top elements.

Total averaged Insertion Loss for the sound absorbing screen top element for the distances 6, 12 and 18 metres from the screen

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Figure 2. The Insertion loss of the cylindrical absorbing screen top element in each 1/3-octave band.

The insertion loss has also been determined for existing traffic noise measured by a logging device during several days. The measured mean value of the insertion loss was about 2 (1.9) dB(A) or about half of what was measured with loudspeaker as sound source. This lower insertion loss is due to the fact that the screen top test section has been too short: The leakage effects due to sound transmitted via the parts of the screen which have not been equipped with the sound absorbing screen top have been simulated. This simulation has been performed using the software CadnaA®. The simulations show that if a longer section had been equipped with the sound reducing screen top, the traffic noise would give the same (about 4-5 dB(A)) extra screen reduction that has been measured with the loudspeaker as sound source.

The technology reported in this delivery seems to be well worth to be further developed and tested in a larger scale.

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3 A C O U S T I C G A L L E R I E S In some situations where there are residents close to a road with dense traffic, normal sound reducing measures like screens may not be enough.

Examples of such situations could e.g. be a four lane highway with allowed vehicle speeds of 90-120 km/h, a traffic density of 40000 vehicles/day and with residents 15-20 m from the road edge. In order to reach design goals of Lden ≤ 55-60 dB(A) for such cases it can be advantageous to apply the Acoustic Gallery concept

An Acoustic Gallery is a tunnel-like covering of the entire road just leaving enough openings for ventilation and daylight. Inside the Acoustic Gallery a diffuse sound field is generated. The material on the inside surfaces of the screens and “ceiling” are lined with sound absorbing material thus creating a chamber attenuation effect. The absorption inside the Acoustic Gallery will then reduce the total radiated sound power from the road (which is not the case for a non-absorbing normal screen installation). The emitted sound from the opening will have a distinct vertical directivity, which in turn further enhances the attenuation perceived by the nearby residents.

Figure 3 below shows a conceptual sketch of an Acoustic Gallery solution. Of course It is important to create the necessary free height to the overhang. For overhang of several meters the mechanical load support could also be provided by bars or girders between the edges of the overhang.

Figure 3. Conceptual sketch of the an Acoustic Gallery solution.

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3.1 RAY TRACING CALCULATIONS AND RESULTS 3D-models with normal roadside screens and with an Acoustical Gallery have been created. The 3D-model for the Acoustical Gallery is seen in Figure 4 below. The traffic noise is modelled with two line sources for each lane (one line source for each wheel).

Figure 4 A view of the 3D model used for ray-tracing calculations of the excess noise reduction due to the Acoustic Gallery overhang.

Ray tracing calculation results for the Acoustic Gallery concept is presented in Figure 5. Figure 6 presents ray tracing calculation for normal non-absorbing screens and Figure 7 presents the calculated difference between normal roadside screens and the Acoustical Gallery.

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Figure 5. Sound levels from a highway with 58000 vehicles/day with a 4 m high screen with 5 m overhang. Sound absorbing material of twin layer typ assumed mounted on the inside. Calculation with aid of ray-tracing technique.

Note the efficient shadow zone with equivalent sound levels below 50 dB(A) shown in Figure 5. Note also the strong vertical directivity that can be seen for the sound emitted from the top of the enclosure

Figure 6. Sound levels from a highway with 58000 vehicles/day with a 4 m high screen without overhang. Sound absorbing material of twin layer typ assumed mounted on the inside of the screen. Calculation with aid of ray-tracing technique.

35 42.5 57.550 65 72.5 80 87.5 95

Overall A-weighted sound pressure level [dB(A)]

35 42.5 57.550 65 72.5 80 87.5 95

Overall A-weighted sound pressure level [dB(A)]

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Figure 7. Sound levels difference from an Acoustic Gallery with 5 m overhang relative to the normal screen 4 m high without overhand. Sound absorbing material of twin layer typ assumed mounted on the inside of the screen and inside of overhang. Calculations performed with the aid of ray-tracing technique.

Note the high excess attenuation due to the overhang shown in Figure 7. The difference at the ground level is of size-order 10 dB(A)-units. Above the 4 metre level the difference is higher with excess attenuations of 15 dB(A)-units. The Acoustic Gallery concept seems to be a good technique to ensure low sound levels also for the upper floors in multi-storey buildings.

3.2 SOME BASIC CONCLUSIONS BASED ON THE RAY-TRACING CALCULATIONS. From the ray-tracing calculations can be seen that:

• An Acoustic Gallery with 5 metre overhang will give 10-15 dB(A) more noise reduction relative a normal screen without any overhang. 10 dB(A) is obtained at the ground level while up to 15 dB(A) can be achieved at 4-7 meters above ground.

• The overhang creates high excess attenuation also at higher levels above ground, 4-7 metres from the ground level. This is an important effect since all noise maps produced in compliance to the EC Directive 2002/49 shall state the Lden levels in dB(A) at 4 metres above ground.

• The Acoustic Gallery supplied with efficient sound absorption will also give a reduction of the total emitted sound power from the road. This may result in a lowering of sound levels also at greater distances from the road at unfavourable wind and temperature gradients.

• The sound emission from the opening of the Acoustic Gallery has a marked vertical directivity which further enhances the excess attenuation at low wind and temperature gradients.

• The excess screen attenuation given by the Acoustic Gallery overhang would also call for an increase of the sound reduction index for air-borne sound through the screen material (not to be mixed up with the diffracted sound at the screen top). For a screen giving 15-20 dB(A) as insertion loss a sound reduction index R´w of 25-30 dB would be required. However for a further increase of the insertion loss

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Difference in Overall A-weighted sound pressure level [dB(A)]

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due to Acoustic Gallery installations the sound reduction index should be at least 35 – 40 dB. This would normally require some attention to the design of the wall structure in order to ensure that the desired sound reduction index is actually reached.

3.3 OTHER EXAMPLES ON HOW THE ACOUSTIC GALLERY CONCEPT COULD BE APPLIED. The use of buildings to provide screening of traffic noise will be subject to special studies in the QCITY WP 4.2. However buildings near noisy primary roads could preferably be designed with overhang and sound absorbing façade surfaces in order to create extra high excess noise attenuation to the shadow zones behind the buildings.

Below is given an architects view of how Acoustic Gallery effects could be implemented by special design of office buildings and a parking house. The examples are shown in Figure 8 and Figure 9 below.

Figure 8. Various layouts of office buildings surrounding a densely trafficed arterial road in order to create the Acoustic Gallery effect. The inside surfaces toward the road shall be covered by sound absorbing façade materials.

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Figure 9. The overhang part of the buildings over the road can be used as e.g. parking house. If the inside surfaces towards the road are covered by with sound absorbing façade materials. Thereby an efficient noise reduction mitigation method is created.

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4 T R A I N A N D T R A M S C R E E N S - S O U N D A B S O R P T I O N F O R E L I M I N A T I O N O F C L I M B I N G R E F L E X E S

4.1 BACKGROUND In many standard calculation models for predicting noise from railway lines (e.g. the Nordic prediction model for train noise) the influence of the train itself is neglected. For many cases this simplification has little effect on the precision in the calculation of the sound level at nearby houses.

However in the case of flat screens without sound absorption, the absence of the train car body can cause substantial calculation errors. The error is caused by repeated reflexes between the screen side and the train car body side. In order to bring this problem to attention for those who are going to create noise action plans we decided to include a study of the phenomenon with the aim to quantify the order magnitude of the error.

The effect of efficient absorption on screens for trains and trams has been studied by ray tracing calculations. Because of the climbing reflexes between the screen and the train/tram car body, the screen sound absorption has extra effect in case of train and tram applications compared to e.g. road traffic screens1.

4.2 “CLIMBING” REFLEXES Climbing reflexes (see Figure 10) between the reflecting inner side of the screen and the train or tram car body will cause the sound energy to pass the screen edge with smaller angles (a more horizontal direction) compared to the direct sound propagation path. This means that climbing reflexes would affect sound levels at the 2nd or the 3rd floors in multi-storey buildings. The influence from diffraction at the screen edge could also be more unfavourable with respect to sound levels in close positions behind the screen.

1 In connection with road traffic climbing reflexes can also occur for trucks with huge flat car body sides.

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Figure 10. The effect of climbing reflexes shown in a ray tracing calculation (the ray is marked green in the picture). The train model used in these calculations are the train at “Roslagsbanan” which is a narrow track network in serving at the northeastern part of greater Stockholm.

4.3 THE SOUND ABSORBING MATERIAL OF TWIN LAYER TYPE. The reference screens assumed in the calculations are a standard wooden design without sound absorption material on the traffic side. The absorption material assumed for the screens in the calculations are a twin layer design (see Figure 11) in which the material combination has been optimized for a maximum of sound absorption and weather resistance.

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Figure 11. Picture of the tested twin-layer sound absorbing material.

The absorption factor of the two layer absorptive material has been measured in an impedance tube with the two microphone method, see Figure 12.

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Figure 12. Measured absorption factor of the twin layer absorption material aimed for covering of the screen inside. The twin layer design consists of 1 Rockdelta mineral wool board 80 mm thick of density 140 kg/m3 2 Paroc 1303 mineral wool board 45 mm thick and of density appr 50 kg/m3

• Plastic net with high percentage open area for mechanical protection.

• Outer layer of absorber with low flow resistance

• Inner layer of absorbing material with high flow resistance.

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4.4 CALCULATIONS WITH AID OF RAY TRACING A 3D-model of the local train (Roslagsbanan (Rb) operating on the SL narrow track network in the north east area of greater Stockholm) was used to perform the ray tracing calculations. The ray tracing software RayNoise from LMS has been used for the calculations. The 3D-model built for calculations with aid of RayNoise is supplied with screens on both sides of the track as shown in Figure 13.

Figure 13. The 3D-model for calculations with aid of RayNoise with screens on both sides of the track. The blue circles indicate the location of the sound sources. See Figure 14 for more details and better resolution.

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Figure 14. Locations of the sound sources in the 3D-model for calculation of the sound emission from a train passage. Axi-symmetry is utilzed in the calculations. We therefore use sources only at one side of the model.

The source locations and sound power levels have been fine-tuned to fit to measured sound pressure levels at train passages 10 m from track centre at the “Roslagsbanan” network north of Stockholm. The source strengths are presented in Table 1 below.

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Table 1. Sound sources used in the 3D-model to simulate a train passage.

Linear Sound Power Level [dB re 1pW] in octave bands

Octave band centre frequency [Hz]

Sound sources 63 125 250 500 1k 2k 4k 8k

Sound sources on wheel discs. 3 sources on each disc.

94.6 86.7 87.9 95.8 94.5 88.9 84.2 78.9

Sound sources on the rail. 5 source positions 91.1 83.1 84.4 92.3 91 85.4 80.6 75.3

In order to get a clear picture on the sound propagation over a screen with and without sound absorbing material on the screen inside we show the sound levels on a receiver mesh located as a cross section through the screen and the train in the middle of the wheel bogie as shown in Figure 15 below.

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Figure 15. Sound levels are displayed on a receiver mesh perpendicular to the screen through the train at the middle of the wheel bogie.

Screens of 2.5 m height above the rail have been added to the 3D-model at different distances from the track. Calculations have been performed with normal wooden non absorbing screens. In other calculations sound absorbing material has been added to the screen. Sound absorption factors according to measurements presented in Figure 12 above has then been used. Appendix 1 presents calculated sound pressure levels in dB(A) as cross section colour plots for screens with and without added absorption located 2 meters, 4 meters and 6 meters from the track centre. The sound reducing effect of added absorption as a function of the distance between the track centre and the screen is plotted in Figure 16 and Figure 17 below.

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The sound reducing effect of adding absorption to double sided screens placed at different distances from the track. Receiver position 10 m from track centre.

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Figure 16 Sound reduction due to added absorption to the source side of the screen as a function of the distance between the screen and the track centre. Receiver position 10 m from track centre.

If, for example, a double-sided screen is located 4 metres from the track centre, and the source side of the screen are covered by sound absorbing material, the extra sound reduction is about 8 dB(A) if the receiver position is 4 m above ground.

Note also that even at the greater distance of 6 m the effect is still 3-4 dB(A). This may in many cases be a substantial part of the total insertion loss of the screen at the respective distances.

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Figure 17 Sound reduction due to sound absorption added to the source side of the screen as a function of the distance between screen track. Receiver position 20 m from track centre.

Figure 16 and Figure 17 show that the closer the screens are located relative to the track, the more sound reduction is achieved by the added absorption. It is also revealed that if the screens are closer than about 3.5 m from the track centre (which corresponds to a distance between the car body and the screen of about 2 m), the effect of adding sound absorption increases almost exponentially.

Ray tracing calculations without the train car body in the 3D-model has also been performed. This simulates the effect calculated by e.g. the Nordic prediction model which, as mentioned before, does not take the car body into account. Figure 18 and Figure 19 presents ray tracing calculation results with and without a train car body in the 3D-model. Results from the Nordic Prediction model calculated with aid of the software CadnaA is also presented.

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The Nordic Prediction model in CadnaA

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Figure 18. Comparison of calculation results for screens installed on both sides of the track and with and without the train car body present. Receiver position 10 m from track centre and 4 m above the ground.

Note the good agreement of the absorption effect between the Nordic Prediction method and Ray-Tracing for no train present shown in Figure 18. Note also that the difference in absorption effect, calculated with aid of ray-tracing with and without the train present, is about 2 dB(A) for distances > 3 metres. For distances < 3 metres the effect of including the car body is increased up to as much as 7 dB(A).

Receiver position 4 m above ground.

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Nordic Prediction model in CadnaA, double sidedscreens, 20m

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The Nordic Prediction model in CadnaA

Figure 19. Calculation results for models with and without the train car body, double sided screens. Receiver position 20 m from track centre and 4 m above the ground.

Figure 18 and Figure 19 show that the ray tracing model without a train car body gives similar results as the Nordic Prediction model (which does not include the train car body). When the train car body is taken into account, the sound reducing affect of added absorption increases with about 2 dB(A) for screens at distances > 3 m from the track centre and can be more than 6 dB(A) for screens at distances < 3 m from the track centre. In other words, for screens closer than 3 m from the track centre it is important to include the train car body to correctly calculate the sound reducing effect of adding absorption to the screens.

For a situation with residential areas only on one side of the screen, the Nordic Prediction model will strongly underestimate the effect of added efficient absorption to the screen. Figure 20 and Figure 21 below presents calculation results with the Nordic Prediction model for single and double sided screens.


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The sound reducing effect of adding absorption to screens placed at different distances from the track. Receiver position 10 m from track centre.

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The Nordic Prediction model in CadnaADouble sided screens

The Nordic Prediction model in CadnaASingle sided screens

Figure 20. Calculation results for single- and double sided screen performed with the Nordic Prediction model. Receiver 10 m from track centre.

The sound reducing effect of adding absorption to screens placed at different distances from the track. Receiver position 20 m from track centre.

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The Nordic Prediction model in CadnaASingle sided screens

Figure 21. Calculation results for single- and double sided screen performed with the Nordic Prediction model. Receiver 20 m from track centre.



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The Nordic Prediction model calculates the screening effect by Fresnel theory. If a screen is non-absorbing, the screen attenuation is reduced by 1-5/3d1; d1 is the distance between track and screen. This is why a single sided screen still gives a small sound reducing affect from adding absorption to the screen. The model including the train car body will though give the same high extra sound reducing affect as for double sided screens, since the sound is absorbed when reflecting between the train car body and the screen.

4.5 BENEFITS OF RAILWAY SCREEN SOUND ABSORPTION COMPARED TO ESTIMATED COST This study has shown that 5-10 dB(A) (screens not closer than 3.5 m from the track centre), extra sound reduction compared to normal non-absorbing screens can be achieved by adding efficient sound absorbing material to the source side of flat screens.

The extra cost for this measure is approximately 50-100 €/m2. Bearing in mind that the total noise reduction effect of a screen of this type is 6-10 dB(A) at a cost of 500-800 €/m it appears to be affordable to almost double the screen insertion loss at an additional cost of only 10 – 15 %.

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5 L A N E S C R E E N S

5.1 BACKGROUND TO THE LANE SCREEN CONCEPT It is well known that the key parameter determining the sound attenuation produced by a screen is proportional to the extended screened propagation path compared to the unscreened sound propagation path.

This means that if the screen is mounted close to the sound source then the efficiency of the screen may be high even if the screen is low.

Tyre/road noise is the dominating sound source of today’s road traffic. For passenger cars it dominates typically from 30 km/h and for trucks typically from 40-50 km/h. Since the source height of the tyre/road noise is very low (typically 2-5 cm above the road surface) new possibilities opens up of using low screens close to the vehicle to create substantial noise reduction. Since there is a risk of climbing reflexes between the car and the screen it is important that the screens are given also a sound absorbing function. With sound absorbing screens close to the vehicle the total emitted sound power from the traffic is also reduced.

So, if low absorbing screens are mounted on each side of a lane on e.g. a motorway then sound reduction comparable to a much higher screen at the roadside could be achieved. Low screens located on the lane markings separating lanes will in the continuation be called “Lane Screens”.

Lane Screens are intended to be installed in a noisy hot spot area (a limited area with high traffic noise levels) during a road section typically 100 - 500 metres long. Like many road work sections with lanes separated by low screens for the purpose of redirecting the traffic a road section treated with lane screens will not allow vehicles to change lane.

Lane Screens could be of interest e.g. when

• ordinary screens for appearance reasons is judged not possible or

• where it for any other reason is not possible to mount ordinary roadside screens

• when a low cost alternative to traffic noise reduction is needed

• when the road administration wants to give a rapid response to a noise complaint. We believe that Lane Screens can be installed very quickly both on a permanent and temporary basis.

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5.2 THEORETICAL BACKGROUND The attenuation caused by a screen is generally governed by the extension δ, of the sound path caused by the screen. In the Figure 22 below can be seen how the sound path over the screen is B+C+D and the unscreened path is A. The lengthening of the pathway due to the screen can then be written δ = (B+C+D)-A.

Figure 22. Sketch of unscreened path and prolonged screened path resulting in a sound reduction by the screen.

The sound attenuation caused by the screen in a certain receiver position can be determined by the Fresnel number according to the equation below.

Where:

N = Fresnel number

δ = the prolongation of sound propagation path caused by the screen compared to the unscreened propagation path.

λ = wavelength of sound = c / f where c is the wave speed in air and f is the frequency.

As can be seen from the above equation the Fresnel number is dependent also of the wavelength. This means that for a certain prolongation of the sound path due to the screen we obtain decreased attenuation towards lower frequencies as can be seen from the diagram in Figure 23 below.

A unscreened path

D Path over the screen B Path over

the screen

C Prolonged pathway δ

Source

δλ⋅=

2N

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Figure 23. Attenuation caused by a screen as function of the Fresnel number.

As can be seen from the above figures we would get a high δ if the screen is located either very close to the source or close to the receiver. This knowledge can be utilized by using lower screens located near the source instead of higher screens at greater distances from the source. The sketch in Figure 24 below tries to convey the point that a low screen may in some cases be just as efficient as a much higher screen at some distance.

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1,55

The HIGH screen gives a prolonged path δ = 4.79+0.10+3.90-8.64 = 0.15 m The LOW screen gives the same prolonged path δ = 0.62+0.1+8,07-8.64 = 0.15 m

Figure 24. In this example the low screen and the high screen gives the same δ. This means that the low and the high screen will give the same sound level reduction.

5.3 DESIGN Lane screens might preferably be manufactured by rubber granulate (crumb rubber) from old tyres bound with polyurethane. Manufacturing in polyurethane bounded rubber granulate gives both good sound absorption and good screening. Figure 25 and Figure 26 illustrate how these lane screens can be designed and mounted in a lane. For higher lane screens (0,5 -1,2 metres) a sound insulating core e.g. of 1 mm steel sheet may be necessary.

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Figure 25. Design sketch of 0.4 m high lane screens. Note the rounded shape of the screen edge in order to minimize the diffraction. The Lane Screen can preferrably be manufactured of polyurethane bonded rubber granulate. This gives simulataneously both sound absorption, sound insulation and an impact protection.

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Figure 26. Sketch of multi-lane separated by lane screens. The Lane Screens shown are 40 cm high. In order to generate the same noise reduction by a roadside screen it needs to be at least 1.7 metres high.

5.4 CALCULATIONS In order to evaluate the concept of lane screens, calculations with aid of the software CadnaA has been performed using the Nordic Prediction model for Road Traffic Noise. The calculations have comprised five different heights of lane screens. In the calculations the lane screens have been given an absorption factor of 0.9. Appendix 2 presents calculation results for different configurations of lane screens, centre screen and normal road side screens. Table 2 below presents a summary of sound reduction for lane screens with different heights and the corresponding height for normal roadside screens giving the same sound reduction. Calculations reveal that a lane screen of height 0.5 m would give so high noise reduction that it takes a 1.8 m high non-absorbing roadside screen (placed 4 m from the lane), to give the same sound reduction. This may sound strange at first but the example above where the sound paths for a low lane screen and a high roadside screen are compared should contribute to the credibility of the concept. Furthermore it is the combination of this low screen close to the source and the efficient sound absorption that results in a reduction of the total sound power emitted from the traffic.

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Table 2. Summary of calculation results for lane screens of different heights compared to road side screens giving the same sound reduction.

Lane screen Height [m]

Sound reduction [dB(A)-units]

Equivalent road side screen (4 m from road side) Height [m]

0.1 3 dB(A) 1.2 m

0.2 4 dB(A) 1.35 m

0.3 4 dB(A) 1.5 m

0.4 5 dB(A) 1.65 m

0.5 6 dB(A) 1.8 m Figure 27 below shows the simple 3D-model used for the calculations, with aid of the software CadnaA, of the noise reduction from lane screens compared to roadside screens. In appendix 2 page 4 it is also shown that the two lane screens close to the middle can be replaced by one middle screen of 1.2 m height.

Figure 27. 3D-model in CadnaA for calculation of insertion loss for the lane screens.

Lane screens

Middle screen

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Figure 28 below shows a picture of a manufactured prototype lane screen in polyurethane bounded rubber granulate. Sound measurements on the prototype is planned to be performed in the period 12M – 18M.

Figure 28. Prototype of lane screen manufactured in polyurethane bounded rubber granulate by QCITY Partner CDM in Belgium.

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5.5 BENEFITS COMPARED TO ESTIMATED COST As seen above a 1.8 m high roadside screen would be required to give the same noise reduction compared to 0.5 m high Lane Screens. The roadside screen 1.8 m high would cost approximately 600-800 €/m only on one side of the road and 1200-1600 €/m for the screen installed on both sides of the road.

The costs for Lane Screens manufactured as polyurethane bonded rubber granulate (crumb rubber) could be estimated to about 110 €/m. For a motorway with four lanes there would be required 6 rows of lane screens. The numbers could be reduced to four if a higher middle screen (height 1.2 m) is installed. This middle screen would probably cost just as much as two lane screens. So the total cost is here estimated to about 650 €/m independently of if there will be a middle screen installed or not.

So for an application where the screen is only needed on one side of the motorway then the cost for the lane screens and the roadside screen should be approximately equal. Still lane screens could be of interest because it is more easy and quick to install and because of the unobstructed sight for nearby residents.

If noise protective screens are needed on both sides of the motorway then the lane screens will be off a noise reduction solution at about half the cost compared to roadside screens.

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6 C O M B I N I N G C R A S H P R O T E C T I O N A N D N O I S E T R E A T M E N T

6.1 BACKGROUND. In many cases crash protection devices of different designs are already installed on many motorways and highways. Below is shown how these already installed crash protection devices could be converted into a fully functional noise screen. This middle noise screen could then be supplemented by lane screens described in chapter 5 above.

6.2 SUPPLEMENTING CONCRETE PROTECTION DEVICES WITH SOUND ABSORBING RUBBER GRANULATE DESIGNS. Crash protection for cars with added rubber granulate for absorption could be a good way of getting noise treatments of “lane screen” concept type, smoothly implemented. Vertically ribbed rubber granulate plates will both add to the safety in the way of adding friction and thus slowing down a car crashing into the protection as well as further increasing the sound absorption and thereby increase the noise reduction. In Figure 29 below is shown a sketch of the conceptual idea.

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Figure 29. A conceptual sketch of a combined noise screen and crash protection. The core of concrete is covered with a mat of rubber granulate bounded by e.g. polyurethane in order that a sound absorbing function is achieved. The rubber mat will serve to further enhance the crash protection capability.

6.3 SUPPLEMENTING CRASH PROTECTING WIRE FENCES WITH SOUND INSULATING AND SOUND ABSORBING RUBBER GRANULATE DESIGNS. Another very common form of crash protection is the wire fences. The wire fences are not very protective for the motorcyclists. In Figure 30 below a sketch of an idea for converting those wire fences to a sound absorbing noise screen is presented. At the same time the new upgraded design will be safer both for passenger car drivers and motorcyclists.

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Figure 30. The above solution for sound absorbing screen can be used to upgrade a wire crash protection device (has become very common e.g. in Sweden in recent years) to a sound reducing screen. The rubber granulate mats will further increase the shock absorbing capability of the combined crash and sound protection device.

We believe that the upgrading of already existing crash protection devices to be a fully functional noise screen could be a cost effective way of providing noise reduction in urban areas. Special effectiveness could be achieved if those upgraded noise screens could be combined with the lane screen concept. An additional feature achieved by updating the wire fences as shown in Figure 30 is that reflections in the road surface from the headlights of oncoming traffic is shielded.

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7 L O W C L O S E F I T T I N G T R A C K S C R E E N S – P L A T F O R M S C R E E N S

7.1 INTRODUCTION TO LOW CLOSE FITTING TRACK SCREENS. For some years now a new concept on reducing noise from train traffic has been utilized. The concept is to install a low screen only 700 mm high very close to the track, only 1700 mm from the track centreline. One example of manufacturer of such screens is one of the partners in the QCITY project, Z-BLOC. They have delivered these screens to a large number of installations, for further information see www.zblocnorden.com).

So the technology is not new though the applications and installations have been regionally limited to Sweden. We think that the technology would deserve a more widespread use.

7.2 THEORETICAL BACKGROUND Just as for the lane screens the attenuation for a close-fitting track screen is generally governed by the path lengthening, δ, of the sound path caused by the screen. See chapter 5 on Lane Screens.

The example in Figure 31 below shows with realistic proportions how a low screen close to the track (1 m high, 0.79 m from track) can be as efficient as a much higher screen at some distance (2.2 m high, 4.25 m from track).

Figure 31. Sketch showing an example with a low screen close to the track and a high screen some distance from the track with the same δ. This means that the low screen close the track/train and the high screen will give the same sound level reduction.

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On top of the pure screening effect governed by the Fresnel number the railway screen will also give other effects that contribute to the excess noise reduction. Among those is e.g. the duct attenuation effect as illustrated in Figure 32.

Figure 32. Conceptual sketch on how a sound attenuating duct is created between the low close-fitting screen and the car body side.

7.3 LOW TRACK-SCREENS AIMED FOR TRAIN TRAFFIC As mentioned before the low close-fitting track screens are already in use in almost ten installation sites in Sweden. So there is by now some experiences on obtained noise reduction as well as a lot of experiences regarding maintenance and operations available.

In the next chapter is reported the measured insertion loss for the Skogås installation in south of Stockholm.

7.3.1 Upgrading the track screen design to meet safety requirements One problem with the close-fitting track screen is that for safety reasons it is not allowed to mount the screen on both sides of the track. There are two main reasons for the limitations:

3. The workers performing track maintenance must have a possibility to escape quickly and safely from the track area. For the previous designs it has been judged that this can only be fulfilled with single sided low track screens.

4. It should be possible to evacuate passengers from a train that has to make an emergency stop between stations

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Since it is believed that the applicability and efficiency of the technology would be much greater if there would be possibilities to mount also double sided low track-screens whenever needed. In order to get permission to do that the above mentioned safety problems must by solved.

Therefore we have upgraded the low close-fitting track screen with escape doors for quick evacuation of the workers from the track area, see Figure 33.

Figure 33. The illustration shows the redesigned low close-fitting track screen with escape doors for quick evacuation of workers from the track area.

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In order to handle evacuation from a train performing emergency stop the top area of the screen has been modified. The screen has now been redesigned so that it has a flat surface on the top like a platform but more narrow, see Figure 34.

Figure 34. The illustration shows the redesigned low close-fitting track screen with a flat upper surface. Note also the stairs enable the passengers to safely step down to the side of the track.

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7.3.2 Measured insertion loss of the low close-fitting track screen. In connection to the planning of a new high school in Skogås south of Stockholm it was revealed that the sound levels on the school yard from a nearby railway line would be too high. Therefore a calculation of the possible noise reduction effect from a low track screen from Z-Bloc was performed.

The calculation revealed that a reduction of 6-7 dB(A) could be expected after installation of the low close-fitting track screens, see Figure 36. Since the railway track was located in a hilly area, as can be seen in Figure 35, the installation of a normal high screen was not an option. Such a screen would have to be 6-8 meter high!

Figure 35. The 3D terrain model used for computer calculations of the sound levels from train traffic. Note also the low track screen marked in the model.

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Figure 36. Calculated insertion loss from the low track screen at the school area. The calculated insertion loss for the school yard was 6-8 dB( A) units. As can be seen in Figure 37 the measured insertion low was found to be substantially higher.

Insertion Loss

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Figure 37. Measured sound levels from passing suburban train. Before and after installation of a low close-fitting track screen. Note that the insertion loss was found to be 11 dB(A). Calculated insertion loss with aid of the software CadnaA and the Nordic Prediction model for train noise was about 7 dB(A). The excess noise attenuation can be due to e.g duct effects and other effects which cannot be handled in the Nordic Prediction model.

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7.4 LOW CLOSE-FITTING TRACK SCREENS AIMED FOR TRAM TRAFFIC. Modern trams with so called low level floors normally also have a car body that covers the bogie area and extends down to just 5-10 cm above the upper edge of the rail.

This new feature of modern trams offers a possibility to mount a very low screen typically not higher than the normal platforms. This type of screen should be supplied with sound absorbing material on the surface towards the tram and be mounted with as small slot toward the tram car body as possible. Normally 2-3 cm greater distance than those of a normal platform has been accepted. It is expected that a total insertion loss of 4-8 dB(A) could be achieved by this design. An artist’s view of the Athens tram with the low tram screen mounted is shown in Figure 38.

This type of noise screens has up to now not been utilized. Therefore a prototype of such a low close-fitting tram screen has been developed, see Figure 39.

Figure 38. An artist’s view of a close-fitting low screen for the Athens tram.

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Figure 39. Measurement site in Athens tram network for testing prototype of low close-fitting tram screens manufactured by Z-bloc. Measurements already completed (see deliverable D 4.3).

The prototype shown in Figure 39 has been tested at TRAM in Athens, see deliverable D 4.3. The measured insertion loss was in the range 6-8.5 dB(A).

These low close-fitting tram screens can be implemented everywhere on the tramline where the normal traffic is not crossing the tram track. Some of the many examples of suitable implementation sites at the Athens tram network for the low close-fitting tram screens are shown in Figure 40. Everywhere where there is grass between the tracks the low close-fitting screens could be mounted.

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Figure 40. Some of the many examples of suitable installation sites for low close-fitting screens at the Athens tram network.

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7.5 BENEFITS COMPARED TO ESTIMATED COST

7.5.1 Close fitting track screens for trains. The cost for the train screen shown here (existing Z-Bloc design) is about 480 €/m. This is about half the cost for a screen 2 m high and 4 m from the track centre.

7.5.2 Close fitting track screens for trams. The cost for the tram screen shown here is about 200 €/m. This is less than half of the cost for a screen 4 m from the track centre giving the same insertion loss.

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8 M E D I U M H I G H T R A N S P E R E N T R E F L E C T I V E N O I S E S C R E E N A reflective transparent screen of a maximum height of appr. 1.7 metres, have been installed on a length of 60m. The installation site was a typical urban area of the network at Glyfada Athens in order to evaluate the relevant noise attenuation characteristics in real commercial operation conditions at constant sped of approx. 20 Km/h. The installation site, measurement procedure etc. is in detail presented in deliverable D 4.3.

Figure 41 below shows the installation site for the medium high transparent noise screens in Glyfada Athens. Figure 42 shows picture from the installation site.

Figure 41. Conceptual sketch showing the Medium Height Transperent Reflective Noise Screen test site

d=3,0m from ext. rail

Channels 3 & 4 15 m from ext. rail 1,2 and 4 m above rail

Channel 2 7.5 m from ext. rail 1,2 above rail

Channel 1 1.0 m from ext. rail 1,2 above rail

Measurement axis

Transparent reflective screen L=60 m

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Figure 42. Pictures of the installation site with some microphone positions.

For this transparent reflective noise screen of appr. 1.7 m height and placed 3 m from the external rail the measured average insertion loss was appr. 9-10 dB(A).

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9 B E N E F I T S C O M P A R E D T O E S T I M A T E D C O S T F O R I N V E S T I G A T E D S C R E E N I N G T E C H N I Q U E S The Table 1 below summarizes cost and performance information for the investigated screening techniques.

Table 3 Performance benefits compared to estimated cost for the investigated screening techniques.

Technique for noise reduction Application

Noise reduction dB(A)

Estimated Cost Euro Comments.

Normal non-absorbing screens


200 €/m2 height < 3m

300 €/m2 height > 3m

At heights > 3 m the foundations for the screen gets much more complicated which increases the cost.

Absorbing cylindrical screen top elements

Road and rail traffic

3-5 dB (in addition to the existing reduction for sharp edged screen)

200 €/meter The diameter of the cylinder must be at least 500 mm

Acoustic Gallery Road traffic >10 dB(A) increase compared to normal roadside screens

300 €/m2

or typically 5000 €/m

road

Absorption added to normal screens

Tram and train traffic

5-10 dB(A) increase of sound reduction compared to non-absorbing screens

50-100 €/m2 (only the absorbing material)

The screen is assumed to be mounted 4-6 metres from the track centreline. For screens closer than 4 m from the track centreline, the effect can be much higher. This effect is underestimated by normal standard prediction models but can be more correctly predicted e.g. by including the train car body.

Lane screens Road traffic 4-6 dB(A) 650 €/meter (4 lane motorway)

(The combined noise treatment/crash protection can replace the two lane screens closest to the road centerline)

Combined noise treatment and crash protection

Road traffic 1-2 dB(A) as stand-alone measure. by itself

200 €/meter Only the additional porous rubber sheets

Works well as a complement to the lane screens

“Platform screens” (screens, 300-400 mm high, close to track)

Tram lines 6-8.5 dB(A) 200 €/meter

“Platform screens” (screens, 700 mm high, close to track)

Train traffic 6-11 dB(A) 480 €/meter Only one-sided screens are presently allowed

Medium high transparent noise screen


70-75 €/m2 (only the material cost) appr. 140 €/m2 (all costs included)

Can be chosen when the esthetical apperance is important and absorbing screens therefore not possible.

deliverable d4.1 12m acl

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