SAT Seminar Feedback Road Noise Study Renaldo Lorio Adrian Jongens Gerrie van Zyl Emile Du Preez

Background 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

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

Scope Study Need Dissemination of information Understand road noise Requirements Effect of different surfacing types Measures to reduce noise levels on N2/6 Recommend strategy Dissemination of information SAT Seminars Summary report after review

Sources of traffic related noise

Summary Understanding road noise Propulsion noise ( Engine, gearbox etc.) Rolling Noise Radial vibrations Air pumping Slip-stick (High frequency effect of tyre on smooth floor)

Summary Rolling noise amplification Horn effect Texture

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 distance Doubling the distance - reduce 3dBA Noise barriers Expensive Partially effective

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 A-weighted sound spectrum levels Sum sound intensities at each frequency

Existing surfacings investigated Existing (old) surfacing types measured 9,5 mm UTFC 13,2 mm UTFC 6,7 mm UTFC 9,5 mm SMA Continuous graded asphalt CGA with rolled-in chips (13,2 mm) 9,5 mm Single seal 13,2 mm Single seal 13,2 + 6,7 mm Double seal

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

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 texture Negative texture

Ideal Affordability ? Microflex 0/6 Porosity 15% Thickness 2.5 cm Twinlay 4/8 – 11/16

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

Existing 19/9 – No loss (Reference) 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

N2/6 Results – Noise Improvement Trials 4.7 dBA

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 improvement Slurry option LAeq = 4.7 dBA (significant reduction)

Strategy Forward Noise mitigation Combined responsibility Land use planning Cost of noise barriers Surfacing type selection Improve rolling noise at source

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