BASELINE NOISE MEASUREMENTS Different Techniques Different Results

BASELINE NOISE MEASUREMENTS Different Techniques Different Results

Assessment Type & Methodology?

Individual Methodologies: BS 4142 PPG 24 BB93 CRTN/DMRB/Road Noise Insulation Regulations CRN/Railway & Guided Transport Systems Insulation Regulations Wind Farm Noise (ETSU-R-97) Noise Act Annex 2 of MPS 2

Multiple Methodologies Required: Environmental Statements Nuisance Investigations World Heath Organisation Guidelines BS 8233

No Established Methodology: Construction Noise AL-72 Perhaps?

Baseline Assessment of Critical Importance for Comparative as opposed to Absolute Assessment Criteria

Individual Methodologies: BS 4142: Almost Exclusively Comparative PPG 24: Absolute BB93: Absolute CRTN/DMRB/Road NIR: Elements of Both CRN/Railway NIR: Elements of Both Wind Farm Noise (ETSU-R-97): Elements of Both Noise Act: Elements of Both Annex 2 of MPS 2: Elements of Both

BS 4142 Index: L A90,T measured using time-weighting F expressed to the nearest decibel Ensure Time Interval sufficient to obtain a representative value May be necessary to repeat the measurements on a number of occasions to obtain a representative sample (especially if meteorological factors potentially significant) Background to be measured at a time typical of that when source will be operating

BS 4142 continued Index: L A90,T measured using time-weighting F expressed to the nearest decibel Clear? Yes Both L Aeq and L A90 rounded in BS 4142 (see 3.1 and 3.10) In reality consultants often reluctant to round L A90 s & L Aeq s where the assessment result critical e.g. Rating Level 49.5 & Background 45.4 is the margin 5 db (rounded) or 4.1 (unrounded)?

BS 4142 continued Ensure Time Interval sufficient to obtain a representative value Under 6 Specific Noise Level, clear Reference Time Intervals are given - 1 Hour during the day and 5 minutes during the night for the Specific Noise Level There is no similar guidance on the Reference Time Interval for Background Noise Level In the absence of guidance many people assume the same Reference Time Interval Is appropriate for both the Specific Noise Level and the Background Noise Level In the absence of any specific guidance it Reasonable to Use the L A90 1 hour And the L A90, 5 minutes at night? for daytime

Measurement Period and L A90 Not Established Industry Practice to do Long Measurement Periods (e.g. 8 hours) No Analytically Correct Way of Combining Percentiles In practice 1 hour, 15 minute or 5 minute L A90 measurements generally taken Average or Minimum 1 hour, 15 minute or 5 minute used for assessment

Measurement Period and L A90 8 hour L A90 significantly lower than Average (shorter period) L A90 s Minimum shorter period L A90 s significantly lower than 8 Hour L A90 The shorter the measurement period, the higher the average L A90 (~ 1dB 5min vs 1hr) The shorter the measurement period, the lower the minimum L A90 The shorter the measurement period, the higher the maximum L A90

Conclusions: Measurement Period and L A90 No Clear Quantitative Guidance on Measurement Period in BS 4142 The Measurement Period for L A90 affects the results Shorter Measurement Periods Give Higher Average L A90 s and Lower Minima L A90 s

BS 4142 continued May be necessary to repeat the measurements on a number of occasions to obtain a representative sample (especially if meteorological factors potentially significant) Wind L Position L Amax Direction Aeq L A10 L A90 F W 66.3 71.3 67.5 64.6 5 SE 57.0 62.5 58.1 55.7 Difference 9.3 8.8 9.4 8.9 Wind Position L Direction Aeq L Amax F L A10 L A90 W 67.7 72.8 69.0 65.9 6 SE 57.3 62.5 59.0 55.5 Difference 10.4 10.3 10.0 10.4

BS 4142 continued Background to be measured at a time typical of that when source will be operating Figure 2: Long-Term Noise Measurement Results 100 90 80 70 60 LAeq Lamax F LA10 LA90 50 Thur 9/9/04 Fri 10/9/04 Sat 11/9/04 40 30 12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00 10:00 12:00

BS 4142 continued Background to be measured at a time typical of that when source will be operating What s Typical when Background Levels Vary with: Time of Day Weather Day of the Week Time of the Year Time Interval Chosen for L A90 Measurements At no point does BS 4142 advise on the use of minimum rather than typical levels

BS 4142 continued Measured at the assessment position(s) or other positions assumed equivalent Positions that are Outside Buildings Representative of the noise level at buildings where people likely to be affected Free-Field Preferred Measurement Height 1.2 1.5m Where measurements above ground floor necessary - 1 metre from facade Apart from measurements having to be made outside buildings there is considerable latitude for interpretation

BS 4142 continued Does the uncertainty regarding background measurement position matter? Is the free-field level representative of the background level at the building? 2 Busy Road 1 Receptor

BS 4142 continued Does the uncertainty regarding background measurement position matter? Is the free-field level representative of the background level at the building (contd)? Background Noise - Many Distant Sources Specific Noise Facade removes 50% of Soundfield 3 db reduction in background Reflection gives up to 3 db Increase Diffuse Field Equal Probability of Sound Arriving from any Direction Predominantly From a Specific Direction Reflection gives up to 3 db Increase Facade Background Lower than Free-Field Facade Rating Level Higher than Free-Field

Baseline for BS 4142: Summary Critical Element of the Assessment Methodology Considerable Variation Can be Obtained in a Specific Location due to: Measurement Position Measurement Time Interval Weather Conditions The way the Results are Processed and Interpreted

PPG 24 ASSESSMENT FOR RESIDENTIAL DEVELOPMENT More Straightforward than BS 4142 Principally Uses L Aeq Difficulty Arises with Specified Measurement Position in Urban Locations Measurements Often Have to be Taken in Elevated Positions (security) 3 db Facade Correction can Result in Apparently Low Free-Field Levels Likely level at the time of application and any increase that may reasonably be expected in the foreseeable future to be determined Measured Noise Levels should be representative of typical conditions

PPG 24 ASSESSMENT FOR RESIDENTIAL DEVELOPMENT Measured Noise Levels should be representative of typical conditions Usually taken to mean mid-week Usually taken to mean dry with light or no wind No Specific Guidance on Measurement Duration Para 8 of Annex 1 confuses some people ( the arithmetic average of recorded readings should be rounded up ) I take this to mean the average of several days readings (not the arithmetic average of short-term L Aeq noise levels to be arithmetically averaged to give the L Aeq, 07:00 23:00 and L Aeq, 23:00 07:00 )

PPG 24 ASSESSMENT FOR RESIDENTIAL DEVELOPMENT NEC noise bands source-specific Additional Requirements Must be able to identify principle influences on daytime & night-time L Aeq Need to know how many events exceed 82 db L Amax S at night Unless dominant noise sources indisputable, requires either: Attended daytime and night-time measurements or periodic audio recordings to enable the principle noise sources to be identified and the capturing of events which exceed 82 db L Amax S at night Question: should the 82 db L Amax S criterion be applied to emergency services sirens in urban locations?

STRATEGIES FOR BASELINE ASSESSMENTS Calculations/Modelling Measurements Combination of Measurements & Calculations Most Baseline Assessments Need an Element of both Measurement & Calculation

CALCULATING BASELINE NOISE LEVELS Requires the Availability of: Source Information A validated model Most Applicable to Transportation Noise

CALCULATING BASELINE NOISE LEVELS Limitations: Availability/validity of traffic data Models generally predict only L Aeq or L A10 (no L Amax for PPG 24 or L A90 for 4142) Most applicable where receptors abut a road or railway for instance Difficult to apply to complex situations (multiple sources/traffic lights/junctions) Doesn t take into account other sources which may affect ambients/backgrounds

BASELINE NOISE MEASUREMENTS Most Reliable Longterm Attended Measurements Attended Samples Reliable but only a Very Limited Snapshot Unattended Longterm Measurements Better Picture of Data over a longer period but Doubt Over Identification of Sources

BASELINE NOISE MEASUREMENTS A Practicable Compromise Establish the Diurnal Pattern of Noise Levels with a Long-Term Unattended Monitor (preferably with periodic and event audio recording) Take sample measurements simultaneously at satellite locations Apply the Diurnal Variation from the Long-Term Measurements to the Sample Noise Measurement Results to obtain an Estimate of the Daytime & Night-Time Noise Levels at each Satellite Location

Period Mon 23 Tue 24 Wed 25 Thu 26 Average L Aeq, 07:00 23:00-57.1 55.9 56.0 56.3 L Aeq, 23:00 07:00 51.1 51.7 51.3-51.4 Table 3.1: Daytime and Night-time L Aeq Noise Levels at the Long-term Measurement Position Sample Long- Daytime Night-Time Time L Aeq L Amax S L A10 L A90 Term Position L Aeq L Aeq, 07 :00 23:0 0 L Aeq, 23:00 07:00 12:15 54.8 60.5 57.1 51.9-1.9 54.4 (A) 49.5 (B) Table 3.2: Noise Levels at Position 1 at a Height of 1.5m Sample Long- Daytime Night-Time Time L Aeq L Amax S L A10 L A90 Term Position L Aeq L Aeq, 07 :00 23:0 0 L Aeq, 23:00 07:00 12:45 54.4 61.7 56.0 51.6-1.6 54.7(A) 49.8(B) Table 3.3: Noise Levels at Position 2 at a Height of 1.5m Time L Aeq L Amax S L A10 L Sample Long- Daytime Night-Time A90 Term Position L Aeq L Aeq, 07 :00 23:0 0 L Aeq, 2 3:00 07 :00 13:20 54.7 60.3 56.3 52.6-1.5 54.8 (A) 49.9(B) Table 3.4: Noise Levels at Position 3 at a Height of 1.5m Sample Long- Daytime Night-Time Time L Aeq L Amax S L A10 L A90 Term Position L Aeq L Aeq, 07 :00 23:0 0 L Aeq, 2 3:00 07 :00 14:00 54.6 59.8 56.4 52.3-1.4 54.9(A) 49.5(B) Table 3.5: Noise Levels at Position 4 at a Height of 1.5m Sample Long- Daytime Night-Time Time L Aeq L Amax S L A10 L A90 Term Position L Aeq L Aeq, 07 :00 23:0 0 L Aeq, 23:00 07:00 15:00 54.5 58.6 55.8 52.6-1.6 54.7(A) 49.8(A) Table 3.6: Noise Levels at Position 5 at a Height of 1.5m

BASELINE NOISE MEASUREMENTS Long-Term Plus Satellites Implicit Assumptions & Cautionary Notes The same noise sources must be the principal influence on the indices being assessed The danger of there being extraneous noise events at the unattended location n.b. Birdsong can play havoc with A-weighted SPLs Be aware of the different attenuation rates of different indices Consider a Road:-

BASELINE NOISE MEASUREMENTS L Aeq /L A10 Line Source L Amax /(L A1?) Point Source - 10 log (distance) i.e. 3 db per doubling of distance - 20 log (distance) i.e. 6 db per doubling of distance

BASELINE NOISE MEASUREMENTS Levels ~ 20m from A-Road Levels ~ 100m from A Road

BASELINE NOISE MEASUREMENTS As you get further from a Line Source (e.g. Road) The Noise Indices get Closer Together The Diurnal Variation of the L A90 Decreases The diurnal pattern of the other indices less distinct (influence of local sources) Long-term Position and Satellite Positions should therefore ideally be comparable distances from the main noise source