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

2. Why undertake an environmental noise assessment?
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. ……

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. Factors affecting received noise levels
Source
(emission)
Transmission
(propagation)
Receiver
(immission)
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. Accounting for temporal variability - noise measurement indices
LAeq,t
LA10,t
LAmax
LA90,t
LAmin

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
Time of Day/Night A B C D
Noise need not be considered
Noise should be accounted for with relevant conditions
Planning permission should not normally be given without good reason and conditions
Planning permission should normally be refused
07: :00
< 55
> 72
23: :00
< 45
> 66
* 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 at the precise time and location 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. variable variable variable 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 quantified e.g. measurement under light downwind conditions promotes slightly higher, more stable noise levels supporting non-acoustic data can be as important as noise data ….

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

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. Sound pressure level, dB(A)
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)
Time of day – 06:00 to 23:00

27. Sound pressure level, dB(A)
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)
Time of day – 06:00 to 23:00

28. Sound pressure level, dB(A) Standard deviation, dB(A)
In general, road traffic noise 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)
Standard deviation, dB(A)

29. Sound pressure level, dB(A)
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)
Time of day – 06:00 to 23:00

30. Sound pressure level, dB(A) Standard deviation, dB(A)
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)
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. Measurement Design Approach
1. Investigate requirement
2. Design
3. Execute
4. Analyse & Report
Review strategy & potential risk
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 to the appropriate level (i.e. the ‘criticality’ of the outcome) and NOT to minimise uncertainty at all costs