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 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

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
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

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 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

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

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