BEDELL CORPORATE TRUSTEES LIMITED AND ATRIUM TRUSTEES LIMITED AS JOINT TRUSTEES OF THE BURTON ROAD UNIT TRUST

Transcription

1 Branston Depot, Burton on Trent BEDELL CORPORATE TRUSTEES LIMITED AND ATRIUM TRUSTEES LIMITED AS JOINT TRUSTEES OF THE BURTON ROAD UNIT TRUST Technical Report 13-IAC002 February 13 Innovate Acoustics is a trading name of Innovate Partnership Limited. Registered office: Innovation Centre, University of Exeter, Rennes Drive, Exeter, EX4 4RN Registered in England No: i

2 Branston Depot, Burton on Trent BEDELL CORPORATE TRUSTEES LIMITED AND ATRIUM TRUSTEES LIMITED AS JOINT TRUSTEES OF THE BURTON ROAD UNIT TRUST Technical Report: 13-IAC002 Issue: 1 Author (signature): Project Manager (signature): Neil Morgan MSc MIOA Neil Morgan MSc MIOA Date: 31 st January 2013 This report has been prepared for the titled project or named part thereof and should not be used in whole or part and relied upon for any other project without the written authorisation of Innovate Acoustics. No responsibility or liability is accepted by Innovate Acoustics for the consequences of this document if it is used for a purpose other than that for which it was commissioned. Persons wishing to use or rely upon this report for other purposes must seek written authority to do so from the owner of this report and/or Innovate Acoustics and agree to indemnify Innovate Acoustics for any loss or damage resulting there from. Innovate Acoustics accepts no responsibility or liability for this document to any other party than the person by whom it was commissioned. The findings and opinions expressed are relevant to the dates of the site works and should not be relied upon to represent conditions at substantially later dates. Opinions included therein are based on information gathered during the study and from our experience. If additional information becomes available which may affect our comments, conclusions or recommendations, Innovate Acoustics reserves the right to review the information, reassess any new potential concerns and modify our opinions accordingly. VERSION CONTROL RECORD Release Description Date Reviewer Author 1 Assessment Principles Report 31/01/2013 KJF NAM ii

3 Table of Contents 1 INTRODUCTION SITE DESCRIPTION POLICY AND GUIDANCE... 4 APPENDIX A GLOSSARY OF ACOUSTIC TERMINOLOGY... 6 iii

4 1 INTRODUCTION 1.1 Innovate Acoustics has been commissioned by Framptons to assess the impact of noise at a site in Branston, Burton-on-Trent, in respect of the impact of predicted changes in road traffic levels along a proposed secondary access to the site, being a cul-de-sac known as Heather Close. 1.2 The exercise has not yet been carried out in full, due to the lack of appropriate weather conditions, during which to undertake the necessary on-site noise measurements; however, this interim document has been prepared to detail the assessment methodology and standards that will be applied. 1.3 Whilst every effort has been made to ensure that this report is easily understood, it is technical in nature; a glossary of terms is included in Appendix A to assist the reader. 1

5 2 SITE DESCRIPTION 2.1 The location and masterplan of the site is shown in Figure 1, which identifies the site in the context of its surroundings and also identifies the proposed secondary access along Heather Close, forming the focus of this assessment. 2.2 The development is residential-led and proposed to occupy a land-locked site, which currently accommodates four large warehouse units, which are to be demolished and replaced with up to 510 residential units. 2.3 The development proposals have progressed thus far on the basis of primary access being gained via Wall Road to the south of the site; however, in order to provide greater accessibility, flexibility and to distribute anticipated traffic impacts a secondary access has been proposed which utilises a cul-de-sac to the north-west of the site, known as Heather Close. This proposal will evidently increase traffic levels along Heather Close and this study, which has been requested by the Local Planning Authority, aims to provide a quantification and assessment of the likely level of change in received noise at receptors in the vicinity of Heather Close. 2

6 Figure 1 Site Plan 3

7 3 POLICY AND GUIDANCE Assessment of Change in Road Traffic Noise - Design Manual for Roads and Bridges. 3.1 The impact of any changes in L A10,18hour road traffic noise levels due to completed development traffic have been assessed in accordance with the principles and guidance presented within the Highways Agency Design Manual for Roads and Bridges (DMRB). 3.2 The DMRB states that The impact of a project at any location can be reported in terms of changes in absolute noise level. In the UK the standard index used for traffic noise is the L A10,18hour level, which is quoted in decibels". 3.3 In order to determine whether changes in traffic noise levels are likely to occur as a result of the Proposed Development, noise levels have been predicted in accordance with the methodology contained within the Calculation of Road Traffic Noise (CRTN) The calculation method uses a number of input variables to predict the L A10,18hour noise level for any receptor point at a given distance from the road. In this assessment however, the key factors are changes in traffic flows and the composition of the traffic (i.e. percentage HGVs). Therefore, the likely increase in road traffic noise levels as a direct result of the Proposed Development has been calculated in accordance with the BNL prediction method detailed in CRTN. This method considers the relative change in noise level for a notional road-side receptor at a distance of 10 m from the kerb and at a height of 1.5 m (free-field). 3.5 The DMRB presents an impact significance matrix for assessing the magnitude of changes in noise level, which is reproduced in Table 1 and has been utilised in this assessment to consider the impact of any changes in road traffic noise levels throughout the construction and demolition period and operation of the Proposed Development. 1 Department of Environment: 1988: Calculation of Road Traffic Noise, HMSO 4

8 TABLE 1 - ROAD TRAFFIC NOISE SIGNIFICANCE CRITERIA Change in Noise Level, db(a) Significance of Effect 0.0 No Change - No Impact Negligible Minor Moderate >5.0 Major Noise Model of Localised Level Change. 3.6 The above assessment will identify the change in generated noise level on specific road links; however, this, while useful, does not present the full picture of actual noise impact, as it does not consider the relative dominance of adjacent sources. 3.7 In order to counter this, the noise change experienced at properties on Heather Court is considered via a noise model, which takes account of the adjacent road traffic sources, as well as the traffic impact on Heather Court itself. The outcome of this assessment of actual change in received noise is represented graphically in the context of the impact significances set out in Table 1, above. 3.8 This assessment is also complemented by noise measurements at and around the receptor locations on Heather Court, so that it is considered in the context of the actual prevailing daytime ambient noise level in the locality. 5

9 APPENDIX A GLOSSARY OF ACOUSTIC TERMINOLOGY Sound Pressure Sound Pressure Level (Sound Level) Decibel (db) A-weighting, db(a) Noise Level Indices L eq,t L max,t L 90,T L 10,T Free-Field Facade Sound, or sound pressure, is a fluctuation in air pressure over the static ambient pressure. The sound level is the sound pressure relative to a standard reference pressure of 20 Pa (20x10-6 Pascals) on a decibel scale. A scale for comparing the ratios of two quantities, including sound pressure and sound power. The difference in level between two sounds s1 and s2 is given by 20 log10 ( s1 / s2 ). The decibel can also be used to measure absolute quantities by specifying a reference value that fixes one point on the scale. For sound pressure, the reference value is 20 Pa. The unit of sound level, weighted according to the A-scale, which takes into account the increased sensitivity of the human ear at some frequencies. Noise levels usually fluctuate over time, so it is often necessary to consider an average or statistical noise level. This can be done in several ways, so a number of different noise indices have been defined, according to how the averaging or statistics are carried out. A noise level index called the equivalent continuous noise level over the time period T. This is the level of a notional steady sound that would contain the same amount of sound energy as the actual, possibly fluctuating, sound that was recorded. A noise level index defined as the maximum noise level during the period T. L max is sometimes used for the assessment of occasional loud noises, which may have little effect on the overall L eq noise level but will still affect the noise environment. Unless described otherwise, it is measured using the 'fast' sound level meter response. A noise level index. The noise level exceeded for 90% of the time over the period T. L 90 can be considered to be the "average minimum" noise level and is often used to describe the background noise. A noise level index. The noise level exceeded for 10% of the time over the period T. L 10 can be considered to be the "average maximum" noise level. Generally used to describe road traffic noise. Far from the presence of sound reflecting objects (except the ground), usually taken to mean at least 3.5m At a distance of 1m in front of a large sound reflecting object such as a building façade. Fast Time Weighting An averaging time used in sound level meters. Defined in BS

10 In order to assist the understanding of acoustic terminology and the relative change in noise, the following background information is provided. The human ear can detect a very wide range of pressure fluctuations, which are perceived as sound. In order to express these fluctuations in a manageable way, a logarithmic scale called the decibel, or db scale is used. The decibel scale typically ranges from 0 db (the threshold of hearing) to over 120 db. An indication of the range of sound levels commonly found in the environment is given in the following table. TABLE A1: TYPICAL SOUND LEVELS FOUND IN THE ENVIRONMENT Sound Level Location 0dB(A) Threshold of hearing 20 to 30dB(A) Quiet bedroom at night 30 to 40dB(A) Living room during the day 40 to 50dB(A) Typical office 50 to 60dB(A) Inside a car 60 to 70dB(A) Typical high street 70 to 90dB(A) Inside factory 100 to 110dB(A) Burglar alarm at 1m away 110 to 130dB(A) Jet aircraft on take off 140dB(A) Threshold of Pain The ear is less sensitive to some frequencies than to others. The A-weighting scale is used to approximate the frequency response of the ear. Levels weighted using this scale are commonly identified by the notation db(a). In accordance with logarithmic addition, combining two sources with equal noise levels would result in an increase of 3 db(a) in the noise level from a single source. A change of 3 db(a) is generally regarded as the smallest change in broadband continuous noise which the human ear can detect (although in certain controlled circumstances a change of 1 db(a) is just perceptible). Therefore, a 2 db(a) increase would not be normally be perceptible. A 10 db(a) increase in noise represents a subjective doubling of loudness. A noise impact on a community is deemed to occur when a new noise is introduced that is out of character with the area, or when a significant increase above the pre-existing ambient noise level occurs. 7

11 For levels of noise that vary with time, it is necessary to employ a statistical index that allows for this variation. These statistical indices are expressed as the sound level that is exceeded for a percentage of the time period of interest. In the UK, traffic noise is measured as the L A10, the noise level exceeded for 10% of the measurement period. The L A90 is the level exceeded for 90% of the time and has been adopted to represent the background noise level in the absence of discrete events. An alternative way of assessing the time varying noise levels is to use the equivalent continuous sound level, L Aeq. This is a notional steady level that would, over a given period of time, deliver the same sound energy as the actual fluctuating sound. To put these quantities into context, where a receiver is predominantly affected by continuous flows of road traffic, a doubling or halving of the flows would result in a just perceptible change of 3 db, while an increase of more than 25%, or a decrease of more than 20%, in traffic flows represent changes of 1 db in traffic noise levels (assuming no alteration in the mix of traffic or flow speeds). Note that the time constant and the period of the noise measurement should be specified. For example, BS 4142 specifies background noise measurement periods of 1 hour during the day and 5 minutes during the night. The noise levels are commonly symbolised as L A90,1hour db and L A90,5mins db. The noise measurement should be recorded using a FAST time response equivalent to ms. 8