Renaldo Lorio Adrian Jongens Gerrie van Zyl Emile Du Preez

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

2. 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

6. 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

7. Scope • Study Need • 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

8. Sources of traffic related noise

10. 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)

11. Summary • Rolling noise amplification • Horn effect • Texture

13. 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

14. Road noise measurements Microphone pre-amplifiers Microphone A-weighted sound spectrum levels Sum sound intensities at each frequency • 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

15. 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

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

18. Ideal Negative texture Positive texture • 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)

19. Ideal 2.5cm 4.5cm Microflex 0/6 Porosity 15% Thickness 2.5 cm Twinlay 4/8 – 11/16 Affordability ?

20. 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

21. Treatments 19/9 + 6.7mm Existing 19/9 – No loss (Reference) 19/9 + Grit 19/9 + Fine Slurry 19/9 Close packing 19/9/9 Split seal

22. N2/6 Results – Noise Improvement Trials 4.7 dBA

23. 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)

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

26. END