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

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. ……

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?

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

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

…. hour by hour ….

…. or day by day ….

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)

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

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

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 - 23:00 < 55 55 - 63 63 - 72 > 72 23:00 - 07:00 < 45 45 - 57 57 - 66 > 66 * N.B. daytime levels LAeq,16hr, night time levels LAeq,8hr

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

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

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

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

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

Need to differentiate between … variability uncertainty risk

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

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 ….

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

Increased uncertainty does not mean increased risk … Range of uncertainty

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

Comparison of measured noise levels 2001/2005

Measurement results 2001 2005

Measurements – 2001 versus 2005

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

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

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) 0.5 1.5 2.5 3.5 4.5 5.5 Standard deviation, dB(A)

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

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) 0.5 1.5 2.5 3.5 4.5 5.5 Standard deviation, dB(A)

Background Sound Variability Noise level, dB Distance from source

Industry Sound Variability Noise level, dB Distance from source

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

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

Guidance…. Investigate requirement Design Survey Survey and Analyse

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

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.)

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

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