The Risks of Environmental Noise Assessments

1. The Risks of Environmental Noise Assessments Presented by Andrew Bullmore Hoare Lea AcousticsCo-authored by Justin Adcock

2. To inform the outcome of some decision making process … research strategic planning complaint resolution specification of noise control measures specification of building element performance compliance testing etc. …… Why undertake an environmental noise assessment?

3. Can noise data help? • the decision making process to be informed must have some ‘target’ outcome • would a knowledge of noise assist in the outcome of the decision making process? • noise may be one of many factors affecting the potential outcome • compared with the other controlling factors, is noise a significant factor? • do planning requirements necessitate the consideration of noise?

4. Specification of building elements External traffic noise levels– PPG24 NEC assessment? Internal noise levels– WHO, BS8233, BB93 etc?

5. but noise in general is not constant ….. second by second

6. …. hour by hour ….

7. …. or day by day ….

8. Source (emission) Receiver (immission) Transmission (propagation) Factors affecting received noise levels • variations in the source (e.g. traffic flows, wet roads) • variations in the propagation path (mainly distance and wind effects) • local effects at the receiver (including cumulative effects of all sources)

9. LAmax LA10,t LAeq,t LA90,t LAmin Accounting for temporal variability- noise measurement indices

10. Temporal variability of noise levels Despite extensive averaging, significant variability in environmental noise levels can still exist from day to day – be warned!

11. PPG24 Noise Exposure Categories (NEC) for traffic noise * N.B. daytime levels LAeq,16hr, night time levels LAeq,8hr

12. Measurement versus Calculation Calculated – constant level Measured – variable levels fourteen days

13. Assessment methodology – measurement • provides an absolute indication of the noise level existing attheprecisetimeandlocation of the measurement • provides a measure of the temporal variability of the sound field over the duration of the measurement period • does not isolate noise from the specific source under study from other extraneous sources • significance of trend changes can be less than natural variability

14. Assessment methodology – prediction • allows isolation of specific noise from other sources • allows trends due to specific source to be positively identified without problems of measurement variability • allows generation of results over wide areas • output results only as good as the input data

15. What is the risk? What if the ‘wrong’ decision were to be made due to ‘incorrect’ or ‘inadequate’ noise data? • money directed towards ineffective strategic .. noise mitigation measures • refusal of planning consent • over / under design of building performance • health implications to the exposed population • enforcement action The design and ‘accuracy’ requirements of any noise assessment should focus on the RISK associated with the outcome

16. What defines ‘accuracy’ in the context of environmental noise? • ‘accuracy’ should be driven by the need to manage ‘risk’ to the appropriate degree • ‘accuracy’ should not be driven by the desire to minimise ‘uncertainty’ at all costs • ‘accuracy’ requirements can therefore only be defined within the context of a particular assessment

17. Need to differentiate between … • variability • uncertainty • risk

18. Variability versus uncertainty Source (emission) Receiver (imission) Propagation • overall noise output level • noise character (tonal, impulsive) • cumulative effects of variable multiple sources • meteorological / seasonal changes (e.g wet roads, holiday traffic, etc.) • meteorological effects • ground effects • screening • mobile sources • cumulative effects of multiple sources in different directions • subjective response / reaction • measurement device accuracy • directional response • exposed population at home or work • windows opened or closed variable variable variable

19. Increased variability does not mean increased uncertainty … …… provided the causes of variability are known and can be quantifiede.g. measurement under light downwind conditions promotes slightly higher, morestable noise levelssupporting non-acoustic data can be as important as noise data ….

20. ISO 9613(based on typical downwind propagation conditions) 20m 200m Calculated noise level, dB 1000m Harmonoise PE model (based onannual measured meteorological conditions) Percentage of time below stated noise level, % Worst case principle adopted by many noise calculation methodologies(downwind propagation)

21. Increased uncertainty does not mean increased risk … Range of uncertainty

22. Noise measurements – summary • 5 x groups of 10 simultaneous measurements • groups arranged either side of main roads (major sources of noise) • simultaneous measurement of meteorological conditions

23. Comparison of measured noise levels 2001/2005

24. Measurement results 2001 2005

25. Measurements – 2001 versus 2005

26. Time of day – 06:00 to 23:00 Scenario 1 – road traffic noise clearly dominates at high level due to proximity of main road 80 75 70 65 60 55 50 45 40 Sound pressure level, dB(A)

27. Time of day – 06:00 to 23:00 Scenario 2 – road traffic noise still dominates, but because road more distant noise is at a lower and more variable level 80 75 70 65 60 55 50 45 40 Sound pressure level, dB(A)

28. In general, roadtrafficnoise demonstrates a strong inverse relationship between absolute noise level and the variability of measured noise levels (see also Alberola et al Forum Acousticum 2004) 80 75 70 65 60 55 50 45 40 Sound pressure level, dB(A) 0.5 1.5 2.5 3.5 4.5 5.5 Standard deviation, dB(A)

29. Time of day – 06:00 to 23:00 Scenario 3 – non- road traffic noise source dominate the overall measured noise levels 80 75 70 65 60 55 50 45 40 Sound pressure level, dB(A)

30. Corruption by non-road traffic noise sources can significantly affect the expected trend in variability 80 75 70 65 60 55 50 45 40 Sound pressure level, dB(A) 0.5 1.5 2.5 3.5 4.5 5.5 Standard deviation, dB(A)

31. Background Sound Variability Noise level, dB Distance from source

32. Industry Sound Variability Noise level, dB Distance from source

33. Uncertainty and Potential Risk critical region = risk Noise level, dB Distance from source

34. 1. Investigate requirement 2. Design Review strategy & potential risk 3. Execute 4. Analyse & Report Measurement Design Approach increasing site knowledge

35. Guidance…. Investigate requirement Design Survey Survey and Analyse

36. Investigate Measurement Requirement • understand the nature of the decision to be made • consider significance of noise in the context of the decision to be informed • understand the nature of the noise value to be derived • review availability of any existing data • review utility of noise measurements as part of a decision making tool

37. Design Measurement Strategy • systematically review all potential sources of temporal or spatial variablity – are they significant? • establish acoustic and non-acoustic information requirements & select appropriate survey method • liaise with commissioning body over potential risks • review requirements against available resources (time/cost/access/equipment/personel/ etc.)

38. Post Measurement Analysis • analyse according to assessment methodology and selected survey strategy • establish if uncertainty equates to risk • review requirement for further studies

39. Conclusions & Summary • always consider the relationship between uncertainty and risk BEFORE attempting any assessment • understand as far as possible the relationship between variability, uncertainty and risk • understanding and quantifying the causes of variability reduces uncertainty • tailor assessment strategies to address risk totheappropriatelevel (i.e. the ‘criticality’ of the outcome) and NOT to minimise uncertainty at all costs