renaldo lorio adrian jongens gerrie van zyl emile du preez sat seminar feedback road noise study

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Renaldo LorioAdrian JongensGerrie van ZylEmile Du Preez

SAT Seminar Feedback

Road Noise Study

MYCUBE ASSET MANAGEMENTSYSTEMS (PTY) LTDMYCUBE ASSET MANAGEMENTSYSTEMS (PTY) LTDBackground

• National road network a generally high speed road network

• Many sections of the national road network traverse in close proximity to residential areas (noise sensitive areas)Development crept closer to the national roads

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Background

• More complaints are being received of late (Mossel Bay, Colchester amongst others)

• In the past road noise was dealt with intuitively (use of OGA and UTFC in close proximity to noise sensitive areas)

• Did not properly understand the properties of the materials w.r.t. noise

• Somewhat averse due to high L.C.C.• Initiated road noise study in 2012

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Scope

• Study Need Understand road noise RequirementsEffect of different surfacing typesMeasures to reduce noise levels on N2/6Recommend strategy

• Dissemination of informationSAT SeminarsSummary report after review

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Sources of traffic related noise

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Summary

• Understanding road noisePropulsion noise ( Engine, gearbox etc.)Rolling Noise

• Radial vibrations

• Air pumping

• Slip-stick (High frequency effect of tyre on smooth floor)

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Summary

• Rolling noise amplificationHorn effect

• Texture

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Noise mitigation

• Minimise at source (most effective)• Speed reduction (e.g.120km/h to 100km/h)

Not significant effect• Half the speed - 2dBA noise reduction

• Separation distanceDoubling the distance - reduce 3dBA

• Noise barriersExpensivePartially effective

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Road noise measurements

• Measurement methods Close Proximity Method

• Cannot be used to calculate LAeq

Statistical Pass-by Method• 7.5 – 10m from lane• 1.4m high

• Results LAmax

Calculation • LAeq

Microphone

Microphone pre-amplifiers

Sum sound intensities at each frequency

A-weighted sound spectrum levels

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Existing surfacings investigated

• Existing (old) surfacing types measured9,5 mm UTFC13,2 mm UTFC6,7 mm UTFC9,5 mm SMAContinuous graded asphaltCGA with rolled-in chips (13,2 mm)9,5 mm Single seal13,2 mm Single seal13,2 + 6,7 mm Double seal

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Results

Note: Values represent only single surveys – Not a representative sample

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Ideal

• Reduce road noise at source Reduce texture depth

• (Within safety limits)

Short & equal wave length (Aggregate size <8mm) Negative texture as far as possible

• Aggregate shape• Construction e.g. Rolling practices

Increase porosity/ interconnected voids and thickness Binder type (Bitumen rubber)

Positive textureNegative texture

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Ideal

Microflex 0/6

Porosity 15% Thickness 2.5 cm

2.5cm

4.5cm

Twinlay 4/8 – 11/16

• Affordability ?

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Seal trials to reduce noise N2-6

• Resealed with 19/9 double seal • Increase in road noise after reseal of N2/6• Complaints• Purpose of this experiment

Improve road noise through seal treatments Measure impact on road noise Measure texture depth and skid resistance

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Treatments

Existing 19/9 – No loss (Reference) 19/9 + Grit 19/9 + 6.7mm

19/9 + Fine Slurry 19/9 Close packing 19/9/9 Split seal

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N2/6 Results – Noise Improvement Trials

4.7 dBA

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Conclusions

• Only one surfacing with LAeq less than 65 dBA

• Seals generally Higher LAeq than paved asphalt

• 9.5 UTFC not performing as expected• Speed does not make a big difference• More measurements required

To determine longer term effects and ranges• N2/6 trials

All trials showed improvementSlurry option LAeq = 4.7 dBA (significant reduction)

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Strategy Forward

• Noise mitigationCombined responsibility

• Land use planning • Cost of noise barriers

Surfacing type selectionImprove rolling noise at source

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