Measurements of Effectiveness of Noise Barriers in Route Sections A to G December 2016 www.erm.com The business of sustainability
Network Rail / Chiltern Railways Measurements of Effectiveness of Noise Barriers in Route Sections A to G December 2016 Reference: 0221083/11/A-G-01 Author: Jack Latham Technical Reviewer: Mike Fraser For and on behalf of Environmental Resources Management Approved by: Ian Gilder Signed: Position: Head of Planning Date: 21/12/2016 This report has been prepared by Environmental Resources Management the trading name of Environmental Resources Management Limited, with all reasonable skill, care and diligence within the terms of the Contract with the client, incorporating our General Terms and Conditions of Business and taking account of the resources devoted to it by agreement with the client. We disclaim any responsibility to the client and others in respect of any matters outside the scope of the above. This report is confidential to the client and we accept no responsibility of whatsoever nature to third parties to whom this report, or any part thereof, is made known. Any such party relies on the report at their own risk. Environmental Resources Management Limited Incorporated in the United Kingdom with registration number 1014622 Registered Office: 2 nd Floor, Exchequer Crt, 33 St Mary Axe, London, EC3A 8AA
CONTENTS 1 INTRODUCTION 1 1.1 SCOPE OF THE ASSESSMENT 1 1.2 GENERAL APPROACH 3 2 NOISE SURVEYS AND DATA COLLECTED 5 2.1 MEASUREMENT LOCATIONS 5 2.2 METHODOLOGY 8 2.3 INSTRUMENTATION AND CALIBRATION 8 3 NOISE BARRIER PERFORMANCE ASSESSMENT 9 3.1 PERFORMANCE ASSESSMENT METHODOLOGY 9 3.2 NOISE MODELLING RESULTS 10 3.3 SUMMARY OF MODELLING RESULTS 18 4 CONCLUSIONS AND RECOMMENDATIONS 20
1 INTRODUCTION 1.1 SCOPE OF THE ASSESSMENT The Chiltern Railways (Bicester to Oxford Improvements) Transport and Works Act Order 2012 authorises the construction and operation of an improved railway between Bicester and Oxford. The planning direction (or deemed planning permission ) is subject to a number of conditions. The work on the Order Scheme is being progressed in 10 individual Route Sections (labelled A J). This document covers Route Section A to G as defined in the approved discharge of conditions document, Discharge of Condition 3 - Sections (Oxford City Council planning reference 13/00918/CND and Cherwell District Council planning reference 13/00106/DISC). The locations of the Route Sections are shown in Figure 1.1. Condition 19(6) requires noise monitoring to be carried out with reference to the Noise and Vibration Mitigation Policy (The Policy). This report outlines the noise barrier testing which has been carried out to check the effectiveness of the noise barriers which have been installed to mitigate noise from Order scheme in Route Sections A to G which lie within Cherwell District Council. The Policy specifies the monitoring to be carried out in para 2.11 as follows (with emphasis added): A noise and vibration monitoring scheme for the Phase 1 and 2A works will be implemented to ensure that the performance of the mitigation measures that are installed achieve the levels of noise mitigation predicted by the design contractor, whose design instructions will include the requirement to achieve the residual noise levels set out in the Environmental Statement.If defects in construction or performance are identified in the first survey, these will be corrected in a timely manner by the contractor. If any defects in construction or performance are found in the second survey, these will also be corrected in a timely manner by the contractor. It is the clear and stated intent of the Policy that the purpose of the noise monitoring is to ensure that the performance of the mitigation is as previously predicted, so that any defects in construction or performance are identified and rectified in a timely manner. 1
Figure 1.1 Route Sections
1.2 GENERAL APPROACH The procedures discussed with Cherwell District Council (CDC) and Oxford City Council (OCC) are contained in Annex A. These included the following key steps: check barriers visually for any defects, measure noise to confirm how barriers will reduce noise for individual trains; and confirm the effect on the overall noise levels. It is important to note that it is the Insertion Loss which is required to assess the performance of a barrier under the Policy. The monitoring is designed to measure insertion loss i.e. the noise difference between the measured noise levels at a receptor with the barrier in place and without it. This involved measurements in an unscreened location above the top of the barriers and behind installed barriers and the residential building that is being protected by the barrier. A distance correction has been applied to the unscreened noise levels to establish the unscreened noise levels at the receptor. In this way the difference between screened and unscreened noise levels was calculated. Also it is worth noting that there is no regulatory standard for field testing of the insertion loss of an acoustic barrier. Therefore, the method of measuring noise from trains and calculating the Insertion Loss has been developed for this project by ERM, based on professional judgement. It was recognised at the outset that there would be some difficulties in calculating and interpreting the results given that this method has not been thoroughly tested in other situations. The concept of identifying significant differences between measured and predicted Insertion Loss values was proposed using a nominal value of 3 db L Aeq as a margin of error or significance threshold in the comparison between measured and predicted performance levels. Differences of less than 3 db L Aeq would also not necessarily indicate a defect in construction. This is reflected in the conclusions of this report, and the methodology was discussed and agreed with Cherwell District Council and Oxford City Council officers on 15 th March 2016. The Insertion Loss has also been predicted for the exact locations at which measurements were made, so that the measured Insertion Loss could be compared to the expected value. These locations are not exactly the same as those for which tabulated results are shown in the Noise Scheme of Assessment, since only some locations were tabulated in that document and the exact locations for monitoring had to be agreed with individual property owners (see Section 2.1). The noise model which was used for the calculation was the one that was developed for the Noise Scheme of Assessment which is based on SoundPlan Version 7.1, which implements the official UK prediction method for railway noise i.e. CRN (1). The model has incorporated the as-built (1) The Calculation of Railway Noise, HMSO, 1995. 3
barrier locations to mirror as accurately as possible the situation which was measured. The noise monitoring results have been modelled to replicate the noise levels expected with the anticipated passenger and freight services, taking into account the measured performance of the barriers. This report sets out the following: Section 2 : details of the noise survey methods and data collected; Section 3 : the assessment of barrier performance; and Section 4: conclusions and recommendations. 4
2 NOISE SURVEYS AND DATA COLLECTED 2.1 MEASUREMENT LOCATIONS Noise measurement locations were agreed with CDC (5 locations near to noise sensitive receptors) (1) and two monitoring points were established at each location to record noise levels (one above barrier, one at second floor window height). The noise measurement locations are shown in Figure 2.1 and are listed in Table 2.1. Figure 2.1 Measurement Locations It was necessary to make minor variations in the exact locations of noise measurement locations because of access restrictions. The final detail of the adopted locations were selected in agreement with residents taking into account preferences for monitoring locations, but they were within a few metres of the locations shown in Figure 2.1 (1) Letter submitted to CDC to advise of noise monitoring locations on 20/05/16 - locations agreed by Trevor Dixon on the 8th of June 2016. 5
Table 2.1 Description of Monitoring Locations Location Address Receptor Height above Nearest Track (m) NCL 1 Whimbrel Close, Bicester Plan Distance from Measurement Location to Nearest Track (m) Notes 3.67 17.52 In rear garden, first floor level NCL 2 Alchester House, Wendlebury 2.64 11.93 In garden, first floor level NCL 3 Oddington Crossing House, Charlton-on- Otmoor 2.47 7.00 In garden to side of house NCL 4 Cherry Trees, Kidlington Road, Islip 8.79 16.5 In garden level at free-field location, but same distance back from track as façade of house. First floor level. Barrier is located on cutting at this point. NCL 5 Mill Street, Islip 2.73 32.32 On patio in garden. The barrier microphone was fixed onto the barrier by use of a pole which raised the monitoring location to a height of 1.5 m above the barrier. 6
Figure 2.2 Monitoring Point above Barrier A typical receptor location monitoring set up is shown in Figure 2.3. 7
Figure 2.3 Monitoring Location at Residential Property (NCL 4) 2.2 METHODOLOGY The noise meters were set up and recorded data within the period from 29 June to 21 July 2016. The types of trains and their configuration were recorded by Network Rail through the use of the TRUST database. Additional information was obtained by Network Rail for the configuration of freight trains as required. Train timetables were also available and these were used to identify trains at the measurement locations. The train noise was recorded as one second L Aeq values and the SEL parameter was calculated for each train pass-by. 2.3 INSTRUMENTATION AND CALIBRATION The noise measurements were taken with Norsonic Nor 140 Sound Level Meters which were used at all locations. The equipment was also set to record audio samples so that the presence of a train could be confirmed when analysing data. The equipment was calibrated before and after measurements using a Norsonic Calibrator. All equipment was supplied with a current laboratory calibration certificate. Calibration was checked on site, and no significant drift was noted. 8
3 A METEOROLOGICAL STATION WAS SET UP TO RECORD WEATHER DATA IN THE AREA OVER THE PERIOD. NOISE BARRIER PERFORMANCE ASSESSMENT 3.1 PERFORMANCE ASSESSMENT METHODOLOGY This Section reports the results of the barrier Insertion Loss measurements and compares the results to the predicted performance. The barriers were found to be free from significant physical defects (i.e. defects which are likely to substantially affect barrier effectiveness at the monitoring locations), and the same barrier material and design is used in all locations. A narrow gap was identified at the base of the barrier at NCL 1 during the second visual survey, which was undertaken after the measurements were made, this could have had some effect on the results. This has now been filled and the effect of this will be quantified in the next monitoring round. The measured data have been converted into screened and unscreened noise levels at each of the five measurement locations. Analysis of individual trains has been carried out, and the results have been averaged over a number of trains. Since the trains showed little variation, only a small number of trains were required at each location. Insertion Losses were developed for freight and passenger trains separately, and then the insertion losses were applied to the calculated unscreened noise levels that were predicted. In this way the effect on overall freight and passenger railway noise levels was calculated. This combined calculation has been based on the assumption that half of the trains travel on each track, and therefore that the unscreened noise from each track at the receptor is similar. If a freight train were to be on power, the CRN calculation method would assume that noise from the train would be emitted at a higher level above the ground. This would mean that the predicted values of barrier Insertion Loss would need to include this factor. This would tend to make the predicted Insertion Loss lower. However, audio recordings of the trains that were analysed suggested that there were no freight trains on power at the five monitoring locations, and noise was assumed to be predominately associated with wheel to rail noise. According to the CRN calculation procedure, the length of trains does not affect the predicted Insertion Loss of a barrier provided that vehicles are all emitting noise from the same source location. In this case all vehicles can be assumed to be emitting noise from the rail/wheel interface and therefore the length of the vehicles does not affect the Insertion Loss which is predicted.. 9
3.2 NOISE MODELLING RESULTS 3.2.1 Introduction The modelled and measured Insertion Losses for individual trains at the five monitoring locations are summarised in Sections 3.2.2 to 3.2.6. 3.2.2 NCL1 Whimbrel Close, Bicester The results for passenger trains are shown below in Table 3.1. Table 3.1 NCL1 Whimbrel Close, Bicester Measured Insertion Loss - db(a) Train 1 6.1-6.9 Train 3 5.6 - Train 6 5.5 - Train 11 7.1 - Train 14 6.5 - Train 19-10.2 Train 21-7.0 Train 22-9.3 Train 24-5.6 Train 25-9.4 Predicted Insertion Loss - db(a) (1) Train 1 10.1-12.1 Train 19-14.5 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1-4.1 - -5.1 Train 3-4.6 - Train 6-4.7 - Train 11-3.0 - Train 14-3.6 - Train 19 - -4.3 Train 21 - -7.5 Train 22 - -5.2 Train 24 - -8.9 Train 25 - -5.1 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. 10
The results for freight trains are shown below in Table 3.2. Table 3.2 NCL1 Whimbrel Close, Bicester Measured Insertion Loss - db(a) Train 1 9.7-8.1 Train 2 9.2 - Train 3-6.4 Train 4-7.8 Predicted Insertion Loss - db(a) (1) Train 1 8.3-9.9 Train 19-11.8 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1 1.3 - -1.8 Train 2 0.9 - Train 3-5.4 Train 4-3.9 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. The results at NCL1 suggest the following: an Insertion Loss of up to 10 db(a) was measured; the Insertion Losses for freight trains cannot be directly compared to those for passenger trains because they run on different lines at this point; the largest deviations from the predicted results was for passenger trains running on the near track; and the deviations from predictions for both tracks suggest the barriers are performing 2 to 5 db(a) less well than expected based on the average value presented for both tracks for passenger and freight trains, but that when the 3 db(a) significance threshold is taken into account, barrier performance is close to being within the accepted margin of variation. 11
3.2.3 NCL2 Alchester House The results for passenger trains are shown below in Table 3.3. Table 3.3 NCL2 Alchester House Measured Insertion Loss - db(a) Train 1 13.3-13.6 Train 3 13.9 - Train 6 13.0 - Train 19-13.5 Train 21-14.0 Train 22-13.7 Predicted Insertion Loss - db(a) (1) Train 1 13.6-14.4 Train 19-17.1 Difference between Measured and Predicted Insertion Loss - db(a) (2) Far Near Both Tracks Train 1-0.3 - -0.8 Train 3 0.3 - Train 6-0.6 - Train 19 - -3.5 Train 21 - -3.0 Train 22 - -3.3 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. The results for freight trains are shown below in Table 3.4. Table 3.4 NCL2 Alchester House Measured Insertion Loss - db(a) Train 1 14.0-11.1 Train 3 14.3 - Train 6-10.8 Train 19-8.8 Predicted Insertion Loss - db(a) (1) Train 1 13.6-14.4 Train 19-17.1 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1 0.4 - -3.3 Train 3 0.7 - Train 6-6.2 Train 19-8.2 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. 12
The results at NCL2 suggest the following: an Insertion Loss of up to 14 db(a) was measured which accords with the predicted insertion loss predicted for the far track; the Insertion Losses for freight trains are similar to those for passenger trains; the largest deviations from the predicted results was for the near track, but very little deviation was observed on the far track results; and the deviations from predictions for both tracks suggest the barrier barriers are performing 1 to 3 db(a) less well than expected based on the average value presented for both tracks for passenger and freight trains, but that when the 3 db(a) significance threshold is taken into account, barrier performance is within the accepted margin of variation. 3.2.4 NCL 3 Oddington Crossing The results for passenger trains are shown below in Table 3.5. Table 3.5 NCL3 Oddington Crossing Measured Insertion Loss - db(a) Train 1 12.6-10.7 Train 3 12.6 - Train 6 11.9 - Train 19-9.3 Train 21-8.3 Train 22-8.7 Predicted Insertion Loss - db(a) (1) Train 1 9.8-10.5 Train 19-11.6 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1 2.8-0.2 Train 3 2.8 - Train 6 2.1 - Train 19 - -2.3 Train 21 - -3.3 Train 22 - -2.9 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. 13
The results for freight trains are shown below in Table 3.6. Table 3.6 NCL3 Oddington Crossing Measured Insertion Loss - db(a) Train 1 8.6-8.9 Train 3 8.5 - Train 6-8.8 Train 19-9.3 Predicted Insertion Loss - db(a) (1) Train 1 9.8-10.5 Train 19-11.6 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1-1.1 - -1.7 Train 3-1.3 - Train 6-2.8 Train 19-2.3 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. The results at NCL3 suggest the following: an Insertion Loss of up to 13 db(a) was measured ; the Insertion Losses for freight were similar to those for passenger trains on the near track, but passenger train Insertion Losses were marginally better on the far track; and the deviations from predictions for both tracks suggest the barrier are performing as predicted for passenger trains and 1.7 db(a) less well than expected for freight expected based on the average value presented for both tracks for passenger and freight trains, but this is well within the agreed significance threshold for this assessment. 14
3.2.5 NCL 4 Kidlington Road, Islip The results for passenger trains are shown below in Table 3.7. Table 3.7 NCL4 Kidlington Road, Islip Measured Insertion Loss - db(a) Train 1 4.4-1.7 Train 3 4.6 - Train 6 6.1 - Train 19 - -1.4 Train 21 - -1.3 Train 22 - -0.8 Predicted Insertion Loss - db(a) (1) Train 1 6.1-6.5 Train 19-7.8 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1-1.7 - -4.8 Train 3-1.5 - Train 6 0.0 - Train 19 - -9.2 Train 21 - -9.1 Train 22 - -8.6 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. 15
The results for freight trains are shown below in Table 3.8. Table 3.8 NCL4 Kidlington Road, Islip Measured Insertion Loss - db(a) Train 1 1.3 - -0.8 Train 2 0.3 - Train 3 - -2.1 Train 4 - -2.0 Predicted Insertion Loss - db(a) (1) Train 1 6.1-6.5 Train 19-7.8 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1-4.8 - -7.3 Train 3-5.8 - Train 6 - -9.9 Train 19 - -9.8 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. The monitoring has shown an anomaly in that there is a negative Insertion Loss at NCL 4 for passenger trains on the near track (see numbers in italics). This suggests that the monitoring method may in some cases under estimate the effectiveness of barriers, and highlights a potential difficulty in undertaking verification measurements in practice. It also brings into question the effectiveness of the monitoring methodology, and therefore, we may need to re-evaluate and assess this in future monitoring rounds. Also, topography and compatibility of this with CRN and Soundplan may be a factor for these unusual results and will be further evaluated prior to the next round of monitoring. The results at NCL4 suggest the following: an Insertion Loss of up to 6 db(a) was measured; the Insertion Losses for freight are lower than those for passenger trains; the largest deviations from the predicted results was for the near track; and the deviations from predictions for both tracks suggest the barriers are performing 5 to 7 db(a) less well than expected based on the average value presented for both tracks for passenger and freight trains. When the 3 db(a) significance threshold is taken into account, barrier performance is only marginally worse than expected. 16
3.2.6 NCL5 Mill Lane, Islip The results for passenger trains are shown below in Table 3.9. Table 3.9 NCL5 Mill Lane, Islip Measured Insertion Loss - db(a) Train 1 16.2-17.8 Train 3 16.4 - Train 6 17.2 - Train 19-16.6 Train 21-19.6 Train 22-19.7 Predicted Insertion Loss - db(a) (1) Train 1 11.8-13.7 Train 19-14.9 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1 4.5-4.1 Train 3 4.6 - Train 6 5.5 - Train 19-1.7 Train 21-4.7 Train 22-4.7 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. 17
The results for freight trains are shown below in Table 3.10. Table 3.10 NCL5 Mill Lane, Islip Measured Insertion Loss - db(a) Train 1 16.1-14.3 Train 3 14.1 - Train 6-14.7 Train 19-13.5 Predicted Insertion Loss - db(a) (1) Train 1 11.8-13.7 Train 19-14.9 Difference between Measured and Predicted Insertion Loss - db(a) (2) Train 1 4.3-0.6 Train 3 2.4 - Train 6 - -0.2 Train 19 - -1.4 (1) Predicted using NSoA model for each track. (2) A positive number indicates the barriers are performing better than predicted. The results at NCL5 suggest the following: an Insertion Loss of up to 20 db(a) for the near track was measured, which is 5 db more than predicted; the Insertion Losses for passenger trains are marginally higher than for freight trains; and the deviations from predictions for both tracks show the barriers are performing 1 to 4 db(a) better than expected. 3.3 SUMMARY OF MODELLING RESULTS The results of the measured insertion losses are summarised in Table 3.11 below. A positive difference between the measured and predicted values indicates the barrier performs better than predicted. Table 3.11 also shows the amount by which this difference exceeds the margin of error or significance threshold, which is up to 3 db (or 3.4 db to one decimal place). It should be noted that this significance threshold value was proposed and agreed with Cherwell District Council and Oxford City Council officers at the meeting on 15th March 2016 before the monitoring was undertaken. 18
Table 3.11 Measured Insertion Losses for Situation on Both Tracks db NCL 1 NCL 2 NCL 3 NCL 4 NCL 5 Passenger Freight Passenger Freight Passenger Freight Passenger Freight Passenger Freight Measured 6.9 8.1 13.6 11.1 10.7 8.9 1.7-0.8 17.8 14.3 Predicted 12.1 9.9 14.4 14.4 10.5 10.5 6.5 6.5 13.7 13.7 Difference -5.1-1.8-0.8-3.3 0.2-1.7-4.8-7.3 4.1 0.6 Net Difference above 3.4 db(a) significance threshold -1.7 N/A N/A N/A N/A N/A -1.4-3.9 +0.7 N/A
4 CONCLUSIONS AND RECOMMENDATIONS The noise barrier Insertion Loss was measured at five locations in Route Sections A to G as agreed with Cherwell District Council. The results were compared to noise modelling predictions using the official UK method (CRN) and the noise model which has been used to produce the approved Noise Schemes of Assessment. No significant physical defects have been found in the barriers (i.e. defects which are likely to substantially affect barrier effectiveness at the monitoring locations), and the same barrier material and design is used in all locations. There is no regulatory standard for field testing of the insertion loss of an acoustic barrier. Therefore, the method of measuring noise from trains and calculating the Insertion Loss has been developed for this project by ERM, based on professional judgement in consultation with Cherwell District Council and Oxford City Council officers at a meeting on 15th March 2016. However, it is recognised that the methodology is somewhat experimental, and further refinements may be required when future monitoring is undertaken. Generally, substantial barrier Insertion Losses of up to 17 db were measured. However, in some cases, the barriers were not as effective as expected based on this round of monitoring using the test methodology. The noteworthy differences are those where the measured Insertion Losses are more than 3 db(a) lower or higher than the predicted values. The noise measurements at four receptors (NCL 1, NCL 2, NCL 3 and NCL 5) are either within, or close to, the 3 db(a) significance threshold or suggest a better measured Insertion Loss than was predicted. However, at one of the receptors, NCL 4, the measured Insertion Loss for freight trains is almost 4 db(a) above the 3 db(a) tolerance band. Differences of less than 3 db(a) can be taken to be a positive indication that there were no defects in construction. The differences at NCL 4 may have been due to topographical issues associated with as-built survey data and/or the noise modelling software. These anomalies will be assessed and refined in advance of the next round of monitoring. 20
In summary, with the exception of NCL 4, the monitoring results were broadly in accordance with the predicted values, and in advance of the next round of monitoring the following steps will be taken: the modelling software and the as-built survey data will be reviewed to establish a rationale for the anomaly at NCL 4; NR will consider monitoring at ground floor level as well as first floor level to evaluate performance of the barrier in a more screened situation; and monitoring will be conducted at more locations to assess if differences are localised anomalies or more widespread, or if they are limited to similar areas to those in which differences were found in this survey round. 21
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