NOISE IMPACT ASSESSMENT OF THE PROPOSED UPGRADING OF THE N2 NATIONAL ROAD BETWEEN KRAAIBOSCH AND DIE VLEIE, EDEN DISTRICT

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1 J KA JO N G E N S K E E T A S S O CI A T E S A C O U S T I CA L E N G I N E E R I N G CO N S U L T A N T S Telephone: Facsimile: jongens@yebo.co.za A.W.D. Jongens 8 Wingerd Avenue 7806 CONSTANTIA Tel/Fax: D. Cosijn 207 Albert Street 0181 WATERKLOOF Tel/Fax: Architectural Acoustics Noise & Vibration Control Environmental Noise Traffic Noise Acoustical Material Research Underwater Sound Nonlinear Acoustics NOISE IMPACT ASSESSMENT OF THE PROPOSED UPGRADING OF THE N2 NATIONAL ROAD BETWEEN KRAAIBOSCH AND DIE VLEIE, EDEN DISTRICT Prepared for The Environmental Partnership on behalf of South African National Roads Agency Limited by A.W.D. Jongens May 2017

2 EXECUTIVE SUMMARY The South African National Roads Agency Limited (SANRAL) is proposing to upgrade the N2 National Road between Kraaibosch and Die Vleie in the Eden District to a four lane, dual carriageway and constructing several road traffic circles along the trajectory. This report presents the results of a Noise Impact Assessment (NIA) into the potential impact of road traffic noise emanating from the proposed upgrade on noise sensitive residential receptors along the road trajectory for the proposed Continuously Graded Asphalt (CGA) and that of an alternative 6.7 mm Ultra Thin Friction Course (UTFC) as noise mitigation procedure. The investigation was conducted in accordance with South African Standard (SANS) 10328, Methods for environmental noise impact assessments. This included the prediction of road traffic noise in accordance with SANS 10210, Calculating and predicting road traffic noise. The results of the calculations were assessed in terms of the World Health Organisation (WHO), SANS 10103, The measurement and rating of environmental noise with respect to annoyance and to speech communication, and the Western Cape Noise Control Regulations (NCR). The results of the investigation indicated that the proposed N2 upgrade utilising a CGA road surface would not significantly alter the existing noise impact on adjacent residential areas. However, in terms of international and local standards the intensity of the noise impact from the existing N2 is high during daytime and ranges between medium and high during night-time. The noise levels would also significantly exceed that permitted by the Western Cape Noise Control Regulations. More than 80% of road traffic noise is due to the interaction between tyres and road surface; called rolling noise. Based on the results of numerous comparative road noise measurements it was found that a porous 6.7 mm UTFC produced the lowest levels of rolling noise of any surface in South Africa. It is anticipated that by replacing the proposed CGA surface with a porous 6.7 mm UTFC this would result in a reduction in noise level at adjacent residential areas by more than 5 db compared to a CGA surface. The intensity of noise impact from the N2 would reduce to low during daytime and night-time. In terms of the NCR the noise levels would still exceed the typical rating level at some residential property boundaries by between 0 and 5 db but, due to the future levels being lower than existing levels, it might be interpreted that they be compliant with Regulation 4. (3) of the NCR. Based on the findings of the investigation it is recommended that the N2 upgrade be surfaced with a well rolled 15% porous UTFC comprising closely packed, uniform sized stones not exceeding 8 mm as outlined in Section 6.1 of this report. SANS 10210, in line with similar international road noise prediction models, is not capable of predicting the effect of traffic circles on road noise. However, a comprehensive review of international literature indicates that the level of noise near a

3 traffic circle is lower than that at traffic light intersection and that of numerous people interviewed there was a distinct preference for traffic circles.

4 TABLE OF CONTENTS 1 INTRODUCTION OUTLINE OF INVESTIGATION LEGISLATIVE FRAMEWORK WORLD HEALTH ORGANISATION SOUTH AFRICAN NATIONAL STANDARDS WESTERN CAPE NOISE CONTROL REGULATIONS, DISTINCTION BETWEEN ASSESSMENT PROCEDURES METHODOLOGY PROCEDURE FOR CALCULATING AND PREDICTING ROAD TRAFFIC NOISE DATA SOURCES LIMITATIONS AND ASSUMPTIONS ROAD TRAFFIC NOISE PREDICTION MODEL EXTENT OF STUDY AREA OMISSION OF IMPACT DURING CONSTRUCTION PHASE LITERATURE REVIEW RELATING TO TRAFFIC CIRCLES ROAD TRAFFIC NOISE AND ROAD SURFACE TEXTURE BASIC REQUIREMENTS FOR A LOW-NOISE ROAD SURFACE DESCRIPTION OF STUDY AREA PREVIOUS NOISE MEASUREMENTS ALONG THE N PREDICTION OF ROAD TRAFFIC NOISE SECTIONS OF ROAD INVESTIGATED TRAFFIC FLOW ROAD SURFACES No noise mitigation - CGA surface With noise mitigation mm UTFC RESULTS OF THE CALCULATIONS ASSESSMENT OF THE RESULTS No noise mitigation With noise mitigation IMPACT ASSESSMENT SUMMARY CONCLUSIONS RECOMMENDATIONS REFERENCES... 28

5 GLOSSARY Terms defined in South African National Standards 10103:2008 and 10328:2008 Ambient noise Definitions the totally encompassing sound in a given situation at a given time, and is usually composed of sound from many sources, both near and far. It includes the noise from the noise source(s) under investigation. A-weighted sound pressure level, LpA A-weighted sound power level, LWA Equivalent continuous A-weighted sound pressure level, LAeq,T Equivalent continuous rating level, LReq,T Reference time interval The sound pressure level, PA, relative to a reference sound pressure, p0, and incorporating an electrical filter network (A-weighted) in the measuring instrument corresponding to the human ear s different sensitivity to sound at different frequencies. It is given by the following equation: LpA = 10 Log p A p 0 2 dba p0 = reference sound pressure = 20 micro Pascal The A-weighted (as above) sound power level, in decibels, emitted by a sound source relative to a reference sound power of W A formal definition is contained in SANS The term equivalent continuous may be understood to mean the average A-weighted sound pressure level measured continuously, or calculated, over a period of time, T. The equivalent continuous A-weighted sound level, LAeq,T, measured or calculated during a specified time interval T, to which is added adjustments for tonal character, impulsiveness of the sound and the time of day. An adjustment of 5 db is added for any tonal character, if present. If the noise is of an impulsive nature an adjustment of 5 db is added for regular impulsive noise and 12 db for highly impulsive noise. Where neither is present, the LReq,T is equal to the LAeq,T. The time interval to which an equivalent continuous A-weighted sound level, LAeq,T, or rating level of noise, LReq,T, is referred. Unless otherwise indicated, the reference time interval, T, is interpreted as follows: Day-time: 06:00 to 22:00hrs T=16 hours when LReq,T is denoted LReq,d Night-time: 22:00 to 06:00hrs T=8 hours when LReq,T is denoted LReq,n 1-hour LAeq or LAeq (1hr) Residual noise District Road traffic noise is measured, predicted and assessed in terms of the LAeq,T for time intervals T = one-hour or multiples thereof. The ambient noise that remains at a given position in a given situation when one or more specific noises (usually those under investigation) are suppressed or absent. Often referred to as background noise. This is related to, but not necessarily equal to, land-use zoning applied in urban and regional planning. For example, mixed-use zoning may comprise a central business district and a residential district.

6 J KA JO N G E N S K E E T A S S O CI A T E S A C O U S T I CA L E N G I N E E R I N G CO N S U L T A N T S Telephone: Facsimile: jongens@yebo.co.za A.W.D. Jongens 8 Wingerd Avenue 7806 CONSTANTIA Tel/Fax: D. Cosijn 207 Albert Street 0181 WATERKLOOF Tel/Fax: Architectural Acoustics Noise & Vibration Control Environmental Noise Traffic Noise Acoustical Material Research Underwater Sound Nonlinear Acoustics NOISE IMPACT ASSESSMENT OF THE PROPOSED UPGRADING OF THE N2 NATIONAL ROAD BETWEEN KRAAIBOSCH AND DIE VLEIE, EDEN DISTRICT 1 INTRODUCTION The South African National Roads Agency Limited (SANRAL) is proposing to upgrade the N2 National Road between Kraaibosch and Die Vleie in the Eden District to a four lane, dual carriageway and constructing several road traffic circles along the trajectory. This report presents the results of a Noise Impact Assessment (NIA) into the potential impact of road traffic noise emanating from the proposed upgrade on noise sensitive residential receptors along the road trajectory for the proposed Continuously Graded Asphalt (CGA) and that of an alternative 6.7 mm Ultra Thin Friction Course (UTFC) as noise mitigation procedure. 1.1 OUTLINE OF INVESTIGATION Presentation of summary of the applicable legal requirements; Methodology of the investigation in accordance with standardised procedures; Limitations associated with applying standardised procedures and the extent of the provided data; Literature review of the benefits of incorporating traffic circles at road intersections; Summary of the overriding effect of road surface texture on road noise emission and the basic requirements to achieve a low-noise surface; Description of the study area including the results of previous road noise measurements; Results and assessment of levels of noise emanating from road traffic on the proposed CGA surface and the alternative 6.7 mm UTFC. 1

7 2 LEGISLATIVE FRAMEWORK In accordance with the Environment Conservation Act 73 of 1989, two procedures exist for assessing and controlling noise, respectively: The South African National Standard (SANS) 10328:2008 Methods for environmental noise impact assessments. The Western Cape Noise Control Regulations (NCR), 2013, P.N. 200 of 20 June SANS 10328:2008 and other South African National Standards relating to noise are incorporated in the NCR and are thereby legally binding. The South African National Standards relating to noise are based on the implementation of recommendations contained in the World Health Organization (WHO) Guidelines for Community Noise. A pertinent summary is included hereunder. The glossary contains definitions of the terminology used in the measurement and assessment of sound/noise. 2.1 WORLD HEALTH ORGANISATION From the collective input of nations throughout the world, including South Africa, the World Health Organization (WHO) has prepared globally applicable Guidelines for Community Noise to serve as the basis for deriving noise standards within a framework of noise management to be implemented at national and regional levels. The Guidelines contain the following summary of thresholds for noise nuisance in terms of continuous outdoor daytime L Aeq in residential districts: At - dba noise creates annoyance. At - dba annoyance increases considerably. Above dba constrained behaviour patterns, symptomatic of serious damage caused by noise, arise. In Chapter 4 of the Guidelines it is stated: To protect the majority of people from being seriously annoyed during daytime, the LAeq on balconies, terraces and outdoor living areas should not exceed dba and not exceed dba to protect them from being moderately annoyed. To avoid sleep disturbance, indoor guideline values for bedrooms are LAeq not to exceed 30 dba for continuous noise. In order for people to sleep with bedrooms open the night-time LAeq at the outside façade should not exceed 40 dba. It will be noted in the next section that the SANS typical day and night-time rating levels for a suburban district are in line with the WHO. 2

8 2.2 SOUTH AFRICAN NATIONAL STANDARDS SANS 10328:2008 contains procedures to be followed to predict the impact of noise of a proposed development based on objective, scientific principles. The predicted impact is assessed in accordance with SANS 10103:2008 The measurement and rating of environmental noise with respect to annoyance and to speech communication by determining whether the rating level, LReq,T, of the noise will exceed the measured residual (background) noise level at recipients or, in the absence of measured residual level, exceed the typical rating level of noise pertaining to the particular district as contained in Table 2 of SANS 10103:2008. If the rating level, LReq,T, of the ambient noise under investigation exceeds the measured and/or the typical rating level, it is probable that the noise would be annoying or otherwise intrusive to a community (such as residents) exposed to the noise. This excess is then related to the probable response of a community to the noise as indicated in Table 5 of SANS Tables 2 and 5 of SANS are reproduced in part hereunder. SANS 10103:2008, Table 2 Typical rating levels for noise in districts Type of district Equivalent continuous rating level (LReq.T) for noise, dba Daynight LR,dn a Outdoors Daytime LReq,d b Nighttime LReq,n b Indoors, with open windows Daynight LR,dn a Daytime LReq,d b Nighttime LReq,n b a) Rural districts b) Suburban districts with little road traffic c) Urban districts 35 d) Urban districts with one or more of the following: workshops; business premises; and main roads 40 e) Central business districts f) Industrial districts SANS 10103:2008, Table 5 Categories of community/group response Excess Estimated community/group response ( LReq,T) a dba Category Description >15 Little Medium Strong Very strong Sporadic complaints Widespread complaints Threats of community/group action Vigorous community/group action In estimating the response of a community (such as residents) to a particular noise under investigation Table 5 of SANS incorporates the diversity of response of individuals of a particular community to the noise level. The estimated response to an 3

9 excess of LReq,T of noise under investigation is thus not in discrete 5 db changes, but in overlapping ranges of excess. The intensity of a predicted noise impact for the EIA process was determined in relation to the categories of community response contained in Table 5 of SANS and is qualified as follows: Negligible Low Medium High Predicted LReq,T does not exceed the typical LReq,T Predicted LReq,T exceeds the typical LReq,T by between 0 & 5 db Predicted LReq,T exceeds the typical LReq,T by between 5 & 10 db Predicted LReq,T exceeds the typical LReq,T by more than 10 db 2.3 WESTERN CAPE NOISE CONTROL REGULATIONS, 2013 Under Land use Regulation 4. (1) The local authority, or any other authority responsible for considering an application for a building plan approval, business license approval, planning approval or environmental authority, may instruct the applicant to conduct and submit, as part of the application (a) a noise impact assessment in accordance with SANS to establish whether the noise impact rating of the proposed land use or activity exceeds the appropriate rating level for a particular district as indicated in SANS 10103; or (b) where the noise level measurements cannot be determined, an assessment, to the satisfaction of the local authority, of the noise level of the proposed land use or activity. (3) Where the results of an assessment undertaken in terms of sub regulation (1) indicate that the applicable noise rating levels referred to in that sub regulation will likely be exceeded, or will not be exceeded but will likely exceed the existing residual noise levels by 5 dba or more - (a) the applicant must provide a noise management plan, clearly specifying appropriate mitigation measures to the satisfaction of the local authority, before the application is decided; and (b) implementation of those mitigation measures may be imposed as a condition of approval of the application. Under Measurement and calculation procedures, Regulation 8 (2) The person taking a measurement may in his or her discretion determine the measuring or calculation point as (a) a point where the complainant is most effected by the noise; or 4

10 (b) a point on the property projection plane of the premises concerned that is representative of the noise matter concerned The noise is accordingly assessed at the measurement point. 2.4 DISTINCTION BETWEEN ASSESSMENT PROCEDURES SANS environmental noise impact assessment procedures are similar to other disciplines whereby the intensity and significance of impact is identified as Low, Medium or High. However, the NCR stipulate a noise level criterion that, by law, may not be exceeded. Either the noise levels comply with the criterion or they do not. In the latter instance noise mitigation procedures must be implemented. The NCR thereby override the relative noise assessments in the EIA process. 3 METHODOLOGY The Noise Impact Assessment (NIA) was conducted in accordance with the South African National Standard (SANS) 10328:2008, Methods for environmental noise impact assessments as prescribed under the National Environmental Management Act Nr 107 of A summary of the procedure is outlined hereunder. 1. Determine the land use zoning and identify all potential noise sensitive receptors that could be impacted upon by the proposed road upgrade. 2. Determine the existing ambient levels of noise within the study area. 3. Determine the typical rating level for noise at identified noise sensitive sites. 4. Calculate the expected rating level of noise due road traffic adjacent to the proposed road upgrade in accordance with SANS 10210:2004, Calculating and predicting road traffic noise. The results are presented by means of noise contours overlaid onto aerial images of the study area. 5. Assess the noise impact on surrounding land and noise sensitive receptors in terms of SANS 10103:2008; the Noise Control Regulations; and the World Health Organisation (WHO). 6. Investigate alternative noise mitigation procedures, where appropriate. 7. Prepare and submit an environmental noise impact report containing the procedures and findings of the investigation. 3.1 PROCEDURE FOR CALCULATING AND PREDICTING ROAD TRAFFIC NOISE The SANS 10210:2004 road noise prediction model was developed from and is essentially the same as the United Kingdom model, Calculation of Road Traffic Noise (CRTN). The model has been validated up to a range of 300 m from a road. Beyond this range the results may still be reported, but the accuracy of the prediction model for ranges greater than 300 m is not defined. 5

11 The factors governing the emission of noise from road traffic utilised in SANS 10210:2004 for the prediction of road traffic noise include: The number of vehicles passing in a time interval (determined for each hour). The mean speed of the vehicles. The percentage heavy-duty vehicles. The road surface texture. The road gradient. The propagation of noise between each noise emission location and each receiver are a function of: Distance between each emission portion of the road and receiver. Intervening topography and structures that may reflect noise towards or shield the noise from the receiver. This was derived from the 3-dimensional Digital Terrain Model (DTM) provided by SMEC. Air absorption Ground effects (including sound absorption of the surface). The LAeq,T due to road traffic noise is calculated for each hour of a 24-hour day. With reference to the glossary the time interval, T, is thus one hour and is termed the 1-hour LAeq or LAeq (1 hr). The daytime Rating Level, LReq,d, is then obtained by averaging (on an energy basis) the sixteen 1-hour LAeq from 06h00 to 22h00. Similarly, the night-time LReq,n is obtained by averaging the eight 1-hour LAeq from 22h00 to 06h00. The topography in the form of a 3-dimensional Digital Terrain Model (DTM) and traffic flow data was input into the computer program SoundPLAN 7.2. Incorporating the CORTN road noise prediction model, with adjustments to conform with SANS 10210:2004, the predicted LReq,d and LReq,n noise contours within the study area were generated. 3.2 DATA SOURCES 1. The 3-dimensional Digital Terrain Model (DTM) was derived from a high resolution LIDAR survey extending 30 m from the outer edge of each carriageway along the road trajectory. The 3-D resolution was 2 mm. The translation and provision of this data by the Cape Town office of SMEC South Africa is greatly appreciated. 2. SMEC also provided traffic flow data obtained from the South African National Roads Agency Limited (SANRAL) Comprehensive Traffic Observations (CTO) Yearbook The nearest Counting Station was 13 Kaaimans Pass. The typical traffic flow for a Friday was chosen as this represented the highest traffic flow during a typical week and thereby representing a worst case scenario of road traffic noise. 6

12 4 LIMITATIONS AND ASSUMPTIONS 4.1 ROAD TRAFFIC NOISE PREDICTION MODEL The road noise prediction model used in this country, SANS 10210:2004, Calculating and predicting road traffic noise is similar to models that are in use by various countries in that it is accurate in predicting the single-figure LAeq for free flowing traffic at constant or near constant speed. However, these models do not enable the influence of uneven driving patterns such as acceleration and deceleration at controlled traffic intersections and traffic circles to be determined. Humans become habituated to environmental noise that in most instances is almost constant and varies but slowly in amplitude and frequency content for extended time periods. An example is free flowing traffic. Although the number of vehicles per hour and the associated levels of noise vary over a 24-hour period, the change in level occurs gradually over part of an hour or longer and the change in loudness is rarely noticed. The LAeq that indicates a long duration average value of noise level correlates closely with humans subjective response to such constant environmental noise. However, humans are sensitive to rapid changes in noise level ( loudness ), whether increasing or decreasing, as well as changes in frequency content (sometimes referred to as character of noise). By rapid is meant that the change occurs within a period of several seconds. When both level and frequency content change together the effect is particularly noticeable. The objectively measured single-figure LAeq value does not adequately relate to these heightened subjective responses that may cause increased annoyance due to interrupted road traffic flow. The influence of interrupted flow is included in the IMAGINE road noise source model (Peeters, v Blokland, 2007) for use by all member states of the European Union. Detailed 1/3 rd octave frequency band (spectrum) levels of each of numerous sources of noise under different driving conditions are measured and entered into a data base. This includes determination of correction factors for acceleration and deceleration for different road gradients. Road traffic noise prediction calculations then combine the spectrum levels of the various sources and applicable correction factors to arrive at a single-figure LAeq value. However, the noise prediction model is significantly more complex than SANS 10210:2004 and the single-figure LAeq value is still the only metric used when assessing the noise. Insufficient collective knowledge and measured data is available to produce additional correction factors that include humans response to the change in level and frequency content occurring during a short time period of seconds as occurs during interrupted traffic flow. The noise prediction model excludes noises produced sporadically and that can not be predicted. Excluded, therefore, are hooting, noise emanating from unroadworthy vehicles, loud music and the particularly the intrusive, high levels of noise produced by certain braking systems (Jacobs engine brake) still used on some heavy vehicles. 7

13 An additional type of sporadic noise that cannot be predicted and therefore modelled is the audible tonal noise emanating from the exposed driveline (gearbox, driveshaft, final drive) of many articulated heavy vehicles. This noise is particularly intrusive during night-time when ambient noise levels are low. Due to the intrusive high noise levels from Jacobs brakes these are prohibited in many countries. Similarly drivelines of all vehicles are to be enclosed. Both fall outside the responsibility of the road agency. 4.2 EXTENT OF STUDY AREA Due to severely limited time for this investigation the study area excluded the sections of road in Kraaibosch and in the Kaaimans Pass and was restricted to the section including Wilderness town through to west of Die Vleie. The provided narrow ribbons of topography limited the ability to adequately assess the predicted noise levels on noise sensitive residential land along the road trajectory. 4.3 OMISSION OF IMPACT DURING CONSTRUCTION PHASE There are many different factors and variables occurring during the construction or upgrading of a road. It would require knowledge of the process (earth moving, grading, surfacing, etc.); details of the type, mechanical power and number of machinery; and estimation of the duration of each activity along each section of the construction process. This information is seldom available in the detail required to enable a realistic prediction of associated noise to be made with any confidence along any section of road construction. Furthermore, the total duration of construction is relatively short. The impact of noise during the construction phase has therefore not been included. 5 LITERATURE REVIEW RELATING TO TRAFFIC CIRCLES A report produced as Deliverable 12 Recommendations on Additional Noise Reducing Measures of the European Union research project SILVIA (SILVIA, 2004) contains a literature survey and evaluation of the effects of various traffic management measures together with the use of noise reducing pavements. Conclusions contained in that report pertinent to the present project are reproduced hereunder within inverted commas with additional comments by this author. 1. A speed reduction reduces noise. This general statement requires qualification. For free-flowing traffic the prediction models including SANS 10210:2004 show that for speeds above km/h the LAeq changes by approximately 1 db for a speed change of 10 km/hr. This is confirmed by the results of this author s measurements. A change of up to 3 db in sound level can hardly be perceived by humans. Thus, a reduction in speed from 80 km/h by 10 or 20 km/h will result in an insignificant reduction in LAeq in terms of human response to sound. 8

14 At approximately 30 km/hr a minimum in noise level due to engine and tyre/road interaction is reached. Below this speed the duration that each vehicle is audible to nearby receptors increases compared to a more rapidly passing vehicle thereby resulting in an increase in LAeq. 2. It is important to achieve as smooth a driving pattern as possible. 3. With reduced speed the noise from some heavy vehicles can in some cases increase due to increased gear shifting, increased propulsion noise and body rattle noises. This author has observed this particularly to be the case when vehicles move up long inclines. An overly restrictive speed limit will result in passenger vehicles as well as heavy vehicles having to change to a lower gear thereby interrupting a smooth driving pattern and increasing propulsion noise two factors that will increase the human response to the noise. 4. Controlled intersections cause deceleration prior to the intersection and acceleration after the intersection resulting in a rapid change in level and frequency content of the noise emitted. This can cause the LAeq to increase by up to 5 db close to the intersection excluding the additional subjective effect of the change in noise level and character. 5. Moderate acceleration re km/h causes approximately 2 db increase in propulsion noise. 6. Changing from an intersection with traffic lights to a traffic circle results in a reduction of 2 to 4 db during daytime and of 2 to 3 db during night-time depending on the percentage heavy vehicles. The reduction in noise is greater for passenger than heavy vehicles. Do not create congestion zones prior to the circle. 7. From results of a subjective study of noise effects comparing controlled intersections and traffic circles it is quite evident that people prefer the sound from a traffic circle. 8. The design of the traffic circle and particularly the radius has an influence on generated noise. High side forces within the circle need to be avoided in order to minimise an increase in tyre/road interaction noise. A report produced as Deliverable 11 of the IMAGINE project (Peeters, v Blokland, 2007) includes information regarding the influence of road surfaces. It includes the statement: The type of road surface significantly influences the noise production of a vehicle. In pass-by events differences up to 15 db(a) are recorded for the same vehicle and speed. The road surface affects mainly rolling noise level, but porous, sound absorbing surfaces will also affect (reduce) propulsion noise. 6 ROAD TRAFFIC NOISE AND ROAD SURFACE TEXTURE More than 80 % of the total sound energy emitted by road traffic is produced by the interaction of vehicle tyres with the road surface, termed rolling noise. Details of the physical factors and mechanisms that produce rolling noise with practical examples to explain the relative levels of noise emitted from different road surface types used in South Africa have been presented elsewhere (Jongens A.W.D., 2008). 9

15 The road surface texture has an overriding influence on two major factors producing rolling noise: 1. Impact noise. During the rolling of a tyre the irregularities of the road surface continuously impact on the tyre setting up vibrations of the tyre walls that are radiated as noise. 2. Air pumping noise. At the leading edge of tyre contact patch the compression of the tyre forces escape of air entrapped between the tyre treads while at the trailing edge air is sucked in as the opposite happens. In order to minimise impact noise the tyre must therefore come into contact with as a smooth a surface as possible. However, this will maximise air pumping noise. A road surface is made up of a mix of stones, often of varying sizes, held together by a binder. Even when initially rolled absolutely smooth, such as a new CGA surface, after some wear individual stones will start to project (termed positive texture) above the mean surface resulting in increased impact noise with time. The amount of impact noise is governed, not by the nominal (average) stone size but by the maximum stone size in the mix; the separation distance between projecting stones; and the depth of the trough (negative texture) between the stones. 6.1 BASIC REQUIREMENTS FOR A LOW-NOISE ROAD SURFACE All of the following requirements are to be met in order to minimise tyre impact noise: The stones should be of constant size and not exceed 8 mm. The stones should have a cubical shape to ensure a flat exposed surface after rolling. Stone chips with sharp edges are to be avoided. The stones are to be closely packed. The mix is to be well rolled to produce an extended mirror smooth surface of the exposed flat faces of stones. The omission of any one of these requirements will result in an increase in the level of tyre impact noise. A porous road surface then provides further reduction of road noise due to 3 separate mechanisms: It provides pressure release within the contact patch area that greatly reduces, if not eliminates, the production of air pumping noise at each end of the contact patch depending on the porosity of the surface. It reduces the amplification of air pumping and other noise radiating away from the source at each end of the contact patch due to a reduced efficiency of the horn effect formed between tyre and road surface. The same effect occurs 10

16 during cupping one s hand around the mouth to project one s voice. This effect is reduced when spreading the fingers of one hand. This is achieved with a standard thickness of ± 20 mm UTFC. A porous road surface would present an extended sound absorbing surface that removes sound energy from the emitted noise initially each time it reflects back-and-forth between the road surface and underside of the vehicle and subsequently as it propagates away from the vehicle over the road surface. An example of a road surface compliant with the requirements is the 6.7 mm UTFC on De Villiers Street, in the residential suburb of Kenridge is displayed in Figure 1. FIGURE 1 Low-noise 6.7 mm UTFC surface of De Villiers Street, Kenridge A 1-hour LAeq of 52 dba was recorded for a mean speed of km/h of 204 vehicles and 0% heavy vehicles; the lowest recorded in South Africa (Jongens A.W.D., 2012). Adjusting for the average 5.7% heavy traffic and average 784 vehicles passing Touwrivier at km/h (refer Table 1) the 1-hour LAeq would be 58 dba; 6 db lower than the average measured at Touwrivier. This represents a significant reduction in terms of human subjective response to noise. 7 DESCRIPTION OF STUDY AREA The study area includes the N2-7 freeway from kilometre post 35.5 just west of Wilderness town to 43.5 just east of the proposed Die Vleie traffic circle. Due to the extent of high resolution topographical data available being limited to 30 m from the outer edge of each carriageway the area available for displaying the predicted noise level contours comprises an approximately 75 m wide ribbon along the N2 trajectory. 11

17 Residential properties are situated at varying distances from the N2 for most of the road trajectory. Some fall within the road ribbon but many are located more than 30 m from the nearest road edge. The existing road surface is Continuously Graded Asphalt (CGA) of varying ages. For the proposed upgrade the intention is to use the same surface. Existing speed limits vary between and 80 km/h between kilometre post 35.5 and To the east of the latter it increases to 100 km/h. 7.1 PREVIOUS NOISE MEASUREMENTS ALONG THE N2 Several sound level measurements have been conducted between the years 2003 and 2012 by the author at several locations within the present study area. All measurements were 1-hour LAeq recorded at a standard distance of 10 m from the road edge between 09h00 and 15h30. The year, location, traffic flow data, mean speed and 1-hour LAeq,T are recorded in Table 1. At km post 40.6 an additional, simultaneous measurement was recorded at a perpendicular distance of 137 m from the N2. Table 1 1-hour LAeq previously recorded in the study area Year & Location Km post Veh/hr % heavy Speed 1hr L Aeq 2003 Touwrivier West of Anchorage Lane Touwrivier Dumbleton Rd (Ebb & Flow) Touwrivier West of Anchorage Lane West of Kleinkranz turnoff East of Serpentine Road th Avenue 137m from N2 (simultaneous measurement) Evident from the table is that the 1-hour LAeq ranged between 62 and 67 dba excepting near Anchorage Lane and Dumbleton Road. The higher levels of 70 and 71 dba were predominantly due to exposed aggregate and cracks in the road surface and less due to traffic flow and speed. The results of numerous road noise measurements have shown that the value of the 1-hour LAeq,T measured 10 m from a particular road section during the middle of the day, outside of the morning and afternoon peak traffic flow periods, closely 12

18 approximates the sixteen hour daytime LReq,d at the same location. The 1-hour LAeq values recorded in Table 1 thus provide a good estimate of the LReq,d with due adjustments for traffic flow and speed. 8 PREDICTION OF ROAD TRAFFIC NOISE 8.1 SECTIONS OF ROAD INVESTIGATED Road sections for which the proposed N2 alignment and adjacent topography were provided are labelled as Sections C through G. Figure 2 records the respective sections included in this study with western and eastern kilometre posts. The provided Section G extended from km 40.1 to The road ribbon and noise level contours would be too small when displaying the entire distance. Only the western portion, Section G West, was included. The displayed noise level contours along this section were representative of the remainder of the complete Section G. Section G West also included the location of previous measured 1-hour LAeq at km post 40.6 contained in Table TRAFFIC FLOW The average night-time hourly traffic flow was approximately 1/9 th that during daytime resulting in the LAeq being approximately 10 db lower during night-time at the same receptor distance. The mean traffic speed used in the calculations was varied between a maximum of 70 km/h midway between largely separated traffic circles to a minimum of 20 km/h within a traffic circle. A speed of km/h was maintained in the vicinity of Wilderness Village (Section C). 13

19 Section C Section D Section E Section F Section G West FIGURE 2 Sections of the N2 highway included in this study with km post values 14

20 8.3 ROAD SURFACES From initial information received it was interpreted that a Continuously Graded Asphalt (CGA) surface with a maximum stone size of 14 mm was to be applied as surface layer to the upgraded N2. This is similar to the existing surface and for which previous 1-hour LAeq values were measured. Refer to Table 1. This surface represented the proposal with no noise mitigation No noise mitigation - CGA surface The results of initial road traffic noise prediction calculations for the proposed N2 upgrade with a CGA surface indicated that the daytime LReq,d and night-time LReq,n exceeded the Typical Rating Levels of noise for a suburban district as stipulated in the NCR. It is pertinent to note that the measured daytime 1-hour LAeq at 10 m from road edge recorded in Table 1 are within the same range as the predicted daytime LReq,d at the same distance thereby providing further confidence in the predicted values With noise mitigation mm UTFC Previous road noise measurements were conducted on what then was termed a 6.7 mm UTFC at two different locations (Jongens A.W.D., 2012; Jongens A.W.D., 2015). It is understood that presently this would be termed a 7 mm UTFC. However, the previous term is retained in this report. Although there were variations in application of the two surfaces with differing road noise level reductions it was anticipated that for the correct application of a 6.7 mm UTFC (refer Figure 1) a reduction of more than 5 db compared to a CGA surface would be achieved for the range of speeds between 20 and 70 km/h considered. From the results of the measurements referred to in the previous paragraph as well as international measurements of porous 6.7 mm UTFC surfaces, a conservative reduction in noise emission level of 5.2 db compared to a CGA surface was applied in the calculations. To date the 6.7 mm UTFC surface emits the lowest rolling noise emission level in this country and represents the most effective noise mitigation procedure available. 8.4 RESULTS OF THE CALCULATIONS The predicted noise level contours are displayed on the following pages. For each of the respective sections the following noise level contours were displayed: Daytime CGA surface; Daytime 6.7 mm UTFC surface; Night-time CGA surface; Night-time 6.7 mm UTFC surface. 15

21 m Figure 3 Section C Daytime CGA m Figure 4 Section C - Daytime 6,7 mm UTFC 16

22 m Figure 5 Section C Night-time CGA m Figure 6 Section C Night-time 6,7 mm UTFC 17

23 0 200 m Figure 7 Section D - Daytime CGA m Figure 8 Section D Daytime 6,7 mm UTFC 18

24 0 200 m Figure 9 Section D Night-time CGA m Figure 10 Section D Night-time 6,7 mm UTFC 19

25 m Figure 11 Section E Daytime CGA m Figure 12 Section E Daytime 6,7 mm UTFC 20

26 m Figure 13 Section E Night-time CGA m Figure 14 Section E Night-time 6,7 mm UTFC 21

27 m Figure 15 Section F Daytime CGA km 39.2 to m Figure 16 Section F Daytime 6,7 mm UTFC 22

28 m Figure 17 Section F Night-time CGA m Figure 18 Section F Night-time 6,7 mm UTFC 23

29 m Figure 19 Section G West Daytime CGA m Figure 20 Section G West Daytime 6.7 mm UTFC 24

30 m Figure 21 Section G West Night-time CGA m Figure 22 Section G West Night-time 6.7 mm UTFC 25

31 8.5 ASSESSMENT OF THE RESULTS With reference to Sections 2.2 and 2.3 the daytime LReq,d and night-time LReq,n at the nearest property boundary along the proposed N2 upgrade should not exceed and 40 dba, respectively. Most of the residential property boundaries are located several to tens of meters from the road edge. For these the following assessments apply: No noise mitigation The results displayed in Figures 3, 7, 11, 15 and 19 indicate that for a CGA surface the daytime LReq,d would exceed dba at many property boundaries by 10 db or more. The associated intensity of noise impact would be high. The results displayed in Figures 5, 9, 13, 17 and 21 indicate that for a CGA surface the night-time LReq,n would exceed 40 dba at some property boundaries by between 5 and 15 db. The associated intensity of noise impact would range between medium and high With noise mitigation The results displayed in Figures 4, 8,12, 16 and 20 indicate that for a 6.7 mm UTFC the daytime LReq,d would range between and dba at some property boundaries with an associated intensity of noise impact being low. The results displayed in Figures 6, 10, 14, 18 and 22 indicate that for a 6.7 mm UTFC the night-time LReq,n would range between 40 and dba at some property boundaries with an associated intensity of noise impact being low. Some isolated residential property boundaries are located close to the road edge and would be exposed to higher LAeq,T values. Examples are a property off Beacon Road and on the corner of Sands Road and the N2 in Section C. The intensity of impact at such properties would be high for both road surface types during daytime and nighttime. The only practical mitigation measure in such cases would be the erection of boundary walls. It is pertinent to note that the application of a CGA surface on the proposed N2 upgrade would result in noise levels at affected property boundaries not being significantly different to the existing noise levels as recorded in Table 1. By contrast compliance with the NCR by applying a low-noise surface would result in a noticeable reduction in noise levels upon commissioning of the upgrade. 26

32 8.6 IMPACT ASSESSMENT SUMMARY Impact Assessment Summary Alternative 1 Without mitigation Alternative 2 With mitigation Description of the impact Noise from CGA surface Noise from 6.7 mm UTFC Nature of impact Negative Positive Intensity High Low Extent Local Local Duration Long term Long term Probability Definite Definite Reversibility Irreversible Irreversible Irreplaceable loss of resources Medium Low Cumulative impact Low Low Significance rating Medium Low 9 CONCLUSIONS The results of the investigation indicated that the proposed N2 upgrade utilising a CGA road surface would not significantly alter the existing noise impact on adjacent residential areas. However, in terms of international and local standards the intensity of the noise impact from the existing N2 is high during daytime and ranges between medium and high during night-time. The noise levels would significantly exceed that stipulated by the NCR. Based on the results of numerous comparative road noise measurements it was found that a porous 6.7 mm UTFC produced the lowest levels of rolling noise of any surface in South Africa. It is anticipated that by replacing the proposed CGA surface with a porous 6.7 mm UTFC this would result in a reduction in noise level at adjacent residential areas by more than 5 db compared to a CGA surface. The intensity of noise impact from the N2 would reduce to low during daytime and night-time. In terms of the NCR the noise levels would still exceed the typical rating level at some residential property boundaries by between 0 and 5 db but, due to the future levels being lower 27

33 than existing levels, it might be interpreted that they be compliant with Regulation 4. (3) of the NCR. SANS 10210, in line with similar international road noise prediction models, is not capable of predicting the effect of traffic circles on road noise. However, a comprehensive review of international literature indicates that the level of noise near a traffic circle is lower than that at traffic light intersection and that of numerous people interviewed there was a distinct preference for traffic circles. 10 RECOMMENDATIONS It is recommended that the N2 upgrade be surfaced with a well rolled 15% porous UTFC comprising closely packed, uniform sized stones not exceeding 8 mm as outlined in Section 6.1 of this report. REFERENCES Peeters, B. and v. Blokland, G., The Noise Emission Model for European Road Traffic. IMATR-0821-MP10, IMAGINE Deliverable 11. SILVIA-DTF-DRI WP D12, SILVIA Deliverable 12: Traffic Management and Noise Reducing Pavements Recommendations on Additional Noise Reducing Measures. Jongens, A.W.D., Road traffic noise measurements of different road surfacing types in the vicinity of Cape Town. Prepared for SANRAL, March 2012 Jongens, A.W.D., Measurement of Road Traffic Noise along the N2 between Harkeville and Nature s Valley turnoff, Western Cape. Prepared for Royal HaskoningDVM on behalf of SANRAL, July Jongens A.W.D., Reducing Road Traffic Noise in South Africa. Southern African Transport Conference, CSIR, July