DPTI Road Traffic Noise Guidelines
Department of Planning Transport and Infrastructure
Road Traffic Noise Guidelines
First published:1990
First Update: February 2002
Second Update: March 2007
Third Update:December 2014
Fourth Update:October 2016
Version: 5
Copyright Department of Planning Transport and Infrastructure
77 Grenfell Street Adelaide, SA 5000
The guidelines were developed by the Environmental Group, Projects Directorate, Safety and Services Division with the assistance of Resonate Acoustics and Roads and Maritime Services.
It has been approved and authorised for use by Departmental staff and its authorised agents by:
General Manager, Asset Management
and endorsed by the Environment Protection Authority..
Extracts may be reproduced providing the subject is kept in context and the source is acknowledged. Every effort has been made to supply complete and accurate information. This document is subject to continual revision and may change.
To ensure you have the most up-to-date version of this document refer to:
For information regarding the interpretation of this document contact:
Asset Management – Technical Services
Telephone: (08) 8343 2686 Facsimile: (08) 8343 2905
TABLE OF CONTENTS
glossary
1introduction
2The nature of road traffic noise
2.1WHAT IS NOISE?
2.2PRESSURE OR LOUDNESS
2.3HUMAN PERCEPTION TO A NOISE LEVEL CHANGE
2.4THE A-WEIGHTED DECIBEL SCALE
2.5TYPES OF ROAD NOISE
2.6FACTORS INFLUENCING ROAD TRAFFIC NOISE GENERATION
2.7NOISE DESCRIPTORS
2.8NOISE MITIGATION MEASURES
2.8.1Noise control at the source
2.8.2Noise control along the transmission path
2.8.3Noise control at the receiver
3Assessment PROCESS
3.1SCOPE OR APPLICATION OF THE GUIDELINES
3.1.1Scope Definition
3.1.2Noise Sensitive Receivers
3.1.3Noise Catchment Areas and Grouping Receivers
3.1.4Responsibility for Mitigating Traffic Noise
3.2NOISE ASSESSMENT CRITERIA
3.2.1Noise Descriptors
3.2.2Noise Criteria
3.2.3Relative Increase Criterion
3.2.4Transitioning Between Noise Catchment Areas with Different Criteria
3.2.5Noise Assessment Location
3.2.6When should Noise Mitigation be considered?
3.2.7Flowchart of Assessment Process
4NOISE MITIGATION DESIGN
4.1ROAD DESIGN
4.2NOISE BARRIERS
4.2.1Barrier Design
4.2.2Noise Barrier Benefit
4.2.3Barrier Materials
4.3PROPERTY TREATMENT
4.3.1Facade Treatment Criteria
4.3.2Facade Treatment Packages
4.3.3Facade Treatments to Noise Sensitive Non-Habitable Spaces
4.3.4Mechanical Ventilation
4.3.5Acoustic Screening
4.4NOISE MITIGATION GENERAL NOTES
5PROCESS FOR ASSESSING ROAD TRAFFIC NOISE
5.1GENERAL
5.2public announcement OF A ROAD PROJECT
5.3NOISE ASSESSMENT BOUNDARY
5.4MODELLING ROAD TRAFFIC NOISE
5.4.1Noise Model Validation
5.4.2Noise Model inputs
5.4.3Road surface corrections
5.4.4Meteorological Effects
5.5DEVELOPMENT OF A NOISE MITIGATION PLAN
5.5.1Reasonable and Practicable Mitigation
5.5.2Community Acceptance
5.5.3Noise Mitigation Plan
5.6DATABASE OF NOISE MITIGATION TREATMENTS
5.7POST CONSTRUCTION VERIFICATION
6.bibliography
APPENDIX A
DPTI Road Traffic Noise Guidelines
glossary
dB / Decibel. A unit of measurement used to express sound level. It is based ona logarithmic scale, which means a sound that is 3 dB higher has twice as much energy.dB(A) / Units of the A-weighted sound level. A-weighting is defined in the International standard IEC 61672:2003 and relates to the measurement of sound pressure level. A-weighting is applied to instrument-measured sound levels in effort to account for the relative loudness perceived by the human ear at typical sound pressure levels, as the ear is less sensitive to low audio frequencies.
EPA / South Australian Environment Protection Authority.
Equivalent
Noise Level - Leq / The Leq is the value of a steady noise that would have the same acoustic energy as the varying noise, over the same time period. All references in these Guidelines are to A-weighted noise levels i.e. LAeq
LAeq (15hr)
(LAeq day) / The noise descriptor refers to the A-weighted energy averaged equivalent noise level over a 15 hour day time period between 7am and 10pm.
LAeq (9hr)
(LAeq night) / The noise descriptor refers to the A-weighted energy averaged equivalent noise level over a 9 hour night time period between 10pm and 7am.
L10 / The noise descriptor L10 refers to the noise level which is exceeded for 10% of the time in a given measurement period, and corresponds to the average of the upper noise levels.
RW / Weighted Sound Reduction Index—A laboratory measured value of the acoustic separation provided by a single building element (such as a partition). The higher the RW the better the noise isolation provided by a building element.
Rw + Ctr / A measure of the sound insulation performance of a building element with a Ctr spectrum adaptation term placing greater emphasis on the low frequency performance.
Insertion Loss (IL) / Insertion loss of barriers is the difference in sound pressure levels at a specified receiver position before and after the installation of barrier, provided that the noise source, terrain profiles, interfering obstructions and reflecting surfaces, if any, have not changed.
Significant / When used in context with a change in noise level, the term ‘significant’ relates to an increase in level of greater than 2 dB(A) (i.e. ≥ 2.1 dB(A))
Residual Exceedance / The remaining exceedance of a noise assessment criterion following the application of noise mitigation measures.
DPTI Road Traffic Noise Guidelines
1introduction
Increasing volumes of traffic and rising community awareness of the environment has led to traffic noise becoming an increasingly important consideration in urban development. The conflicting requirements of providing a quiet environment for people to live in, whilst maintaining a high standard road network for the safe and efficient transportation of increasing numbers of goods and people, presents a challenge to planners and designers involved in land-use planning and road location and design.
As road traffic noise is related to the volume of traffic, high levels are generally associated with the arterial road system. In 2010/11 the South Australian transport task totalled 28.8 billion passenger-kilometres and 37.5 billion tonne-kilometres. Since 2000/01 the South Australian domestic passenger and freight tasks have grown by 5.1% and 17.4% respectively.
Exposure to high traffic noise levels can give rise to various problems, including annoyance from disruption to leisure activities such as listening to music or watching television; speech interference; sleep disruption; decreased work efficiency and proficiency; and fatigue. The control of road traffic noise is therefore seen as having social and economic benefits to the community.
There is, however, a wide range of sensitivity to noise within the community. Some people are likely to be disturbed at relatively low levels of traffic noise, while others may not be disturbed even at relatively high levels. Similarly a range of individual responses could be expected for any given change in noise level. Tolerance to noise is influenced by the degree of acclimatisation, the level and nature of the intruding noise and the level of the background or ambient noise. The annoyance a person feels can also be influenced by the extent to which traffic noise interferes with activities such as reading, sleeping or watching television.
The Department, along with a range of other Federal, State and local agencies has a role in addressing the issue. The Department has a General Environmental Duty under Section 25 of the Environment Protection Act 1993. The Road Traffic Noise Guidelines is the Departments response to satisfying the General Environmental Duty in relation to infrastructure works. The Department will take reasonable and practicable measures to reduce the impact of traffic noise.
Complementary measures being undertaken by the Department to reduce the impacts of road traffic noise include enforcement of in-service vehicle noise emissions, contributing to setting national standards for new vehicles, and measures to manage travel demand and promote alternative modes.
The DevelopmentDivision of DPTI provides guidance to planning authorities, developers and builders on measures that can be adopted to mitigate the impacts of traffic noise. In 2013 the Minister’s Specification SA 78B and the Noise and Air Emissions Overlay policy was introduced to protect sensitive land uses (e.g. residential) from noise emissions generated by major transit corridors. Where the Overlay is applied by Councils through the Development Plan Amendment process this provides protection to new dwellings from traffic noise. Further information is available in Reducing Noise and Air Impacts from road, rail and mixed land use – A Guide for builders, designers and the community.
The Road Traffic Noise Guidelines provides guidance to Departmental staff, consultants and contractors in addressing road traffic noise as a key part of infrastructure project development.
These Guidelines set out the process to be followed and criteria to be applied when assessing the road traffic noise impacts of infrastructure projects involving new roads and/or major upgrading of existing roads. This assessment is to be undertaken during the planning and design phase of such projects and documented in a Noise Mitigation Plan and the Environmental Impact Assessment Report or Project Impact Report, then implemented during construction.
These Guidelines should also be used in conjunction with the Department’s Noise Mitigation Manual that provides details on acoustic issues and design principles in relation to the use of noise barriers and architectural acoustic treatments for noise sensitive properties.
DPTI Road Traffic Noise Guidelines
2The nature of road traffic noise
2.1WHAT IS NOISE?
Noise can be defined as unwanted sound. Sound is the sensation produced in the ear as a result of fluctuations in air pressure, superimposed on the steady atmospheric pressure. The ear responds to these much smaller fluctuations with great sensitivity.
The frequency of a sound is the rate at which the fluctuations occur. Practically all sounds contain a mixture of frequencies. Screeching or whistling noises are composed mainly of high frequency sound while rumbles or booms are composed mainly of low frequency sound. As an illustration, middle C on a piano is 256 Hz (hertz, or cycles per second), while 1,000 Hz is about the frequency of the high C that sopranos strive for.
The auditory senses are normally limited to frequencies between 20 and 20,000 Hz in a young person. The ability to hear the higher frequencies decreases with age, such that it is not uncommon for a 50 year old person to be unable to hear sounds above 8,000 Hz.
2.2PRESSURE OR LOUDNESS
The range of sound pressures (loudness) encountered in everyday life extends from those which the human ear can just detect (the ‘threshold of hearing’) to those many times as great (approaching, and sometimes exceeding, the ‘threshold of pain’). The international standard unit of acoustic pressure is the micropascal (µPa), but as the range between the faintest audible sound and the loudest the ear can stand is so enormous (20 µPa to 63 million µPa), it would be very awkward to express sound pressure fluctuations in these units. Instead, this range is ‘compressed’ by expressing the sound pressure on a logarithmic scale, which is also the way the human hearing mechanism responds to pressure variations.
Sound is therefore described in terms of the Sound Pressure Level (SPL), the unit of which is the decibel (dB). In decibel notation, the entire audible range of sound pressure, described above with such large numbers in micropascals, runs from 0 to 130 dB. Zero decibels is an arbitrary noise energy intensity approximately equal to the lower limit of hearing of a young adult.
It must be remembered that the decibel scale is logarithmic. On a linear scale, the total sound pressure from two identical noise sources would be twice that from one of the sources alone. However, on the logarithmic decibel scale, the total sound pressure level from two identical noise sources is 3 dB higher than the level from either source alone. In other words, in the case of road traffic noise, a doubling of traffic flow leads to a 3 dB increase in the sound pressure level. Similarly, a halving of traffic flow results in a 3 dB decrease.
Although the ear can distinguish change of about 1 dB in a pure tone, the minimum that can be detected for a varying source such as traffic noise is about 3 dB. In addition, each increase of approximately 10 dB sounds subjectively twice as loud to the ear (Refer Section2.3). Therefore a noise measured at 80 dB will sound twice as loud as one which registers 70 dB, which in turn will appear twice as loud as one which registers 60 dB.
Although a risk of temporary or permanent damage exists for people exposed for prolonged periods to noise levels above about 90 dB, higher levels can be tolerated without damage for shorter exposure times.
2.3HUMAN PERCEPTION TO A NOISE LEVEL CHANGE
How we subjectively perceive a change to traffic noise exposure under typical living conditions versus a noise level change is outlined in the table below:
Perceived volume change / Noise level change (dB)Doubling or halving / 6 – 10
Noticeable change / 3 – 5
Not noticeable change / 0 – 2
2.4THE A-WEIGHTED DECIBEL SCALE
Although the perceived loudness of a sound depends primarily on sound pressure, it is also influenced by frequency. The human ear is most sensitive to mid-range and high frequencies (approximately 1,000 – 8,000 Hz) and is less sensitive to the lower frequencies.
To ensure measured levels approximate the human response, a weighting scale is used. It is known as the ‘A’ scale and the units are referred to as ‘A’ weighted decibels (written as dB(A)). The dB(A) scale discriminates between sounds in much the same way as people do.
It should be noted that noise levels (whether predicted or measured) are usually expressed as whole numbers. Decimals below 0.5 should be rounded down, and those equal to or greater than 0.5 should be rounded up to the nearest dB.
Figure 2.1 The “A-Weighted” Curve
The noise levels emitted by vehicles typically varies with frequency, and a typical relationship between noise level and frequency is shown in Figure 2.2.
Figure 2.2 Typical Noise Level - Frequency Relationship
Some examples of typical sound levels in dB(A) are shown in Figure 2.3 below. All further reference to noise levels in these Guidelines will be in dB(A).
Figure 2.3 The level of common sounds on the dB(A) scale
DPTI Road Traffic Noise Guidelines
2.5TYPES OF ROAD NOISE
There are two types of road traffic noise:
(a)from ‘bulk’ traffic flow (i.e. a reasonably continuous stream of vehicles), and
(b)from individual noisy vehicles.
The first occurs on busier roads and manifests itself as a continuous hum or backdrop of noise, although it can have peaks and troughs according to the traffic flow. It is the aggregate noise of all the vehicles in the traffic stream.
The second is produced by single vehicles (typically a high-revving motorbike, a car with a modified exhaust system, or a commercial vehicle’s exhaust brakes) and can occur anywhere and at any time. This may be loud enough to rise above bulk flow traffic noise and can be extremely disruptive, particularly at night in quiet residential areas where sleep can be disturbed.
Although measures can be taken to protect the community against both types, the second is by far the harder to deal with because of the random nature of occurrences, and can only be controlled by vehicle design requirements and in-service monitoring of these requirements. These Guidelines essentially deal with bulk flow traffic noise resulting from normal operation of the road system.
2.6FACTORS INFLUENCING ROAD TRAFFIC NOISE GENERATION
Individual vehicle noise is a combination of noises produced by:
- the engine;
- the transmission;
- the exhaust;
- the interaction of tyres and road pavement;
- air turbulence; and
- body and load rattles.
At lower traffic speeds (typically less than 60km/hr), engine and exhaust noise tend to dominate. Tyre noise is a component of vehicle noise which significantly increases with speed. Studies suggest that at speeds between 30 and 50km/hr, tyre noise of cars is increased to a level which dominates the overall vehicle noise. For trucks, this ‘cross-over’ point tends to occur between 40 and 80km/hr.
Given the increasing stringency of vehicle design regulations on engine and exhaust emissions, tyre noise is increasingly becoming the major factor influencing overall traffic noise. The tyre noise component is highly dependent on tyre / pavement design and on vehicle speed. For heavy vehicles the exhaust outlet location is often elevated, which tends to increase the spread of noise. Air turbulence is not usually important, even at highway speeds.
DPTI Road Traffic Noise Guidelines
Figure 2.4 Passenger car noise sources at speeds below 70km/h (ARRB, 1998a)
Apart from individual vehicle noise, there are five main factors upon which the level of traffic noise depends:
- traffic volume;
- traffic speed;
- traffic composition (i.e. the number of commercial vehicles);
- the road gradient, and
- the pavement surface type and texture.
A change in noise levels may occur if one, or more, of the above factors change.In addition, there are six major factors which influence the propagation of traffic noise:
- the road profile (at grade, depressed or elevated);
- the distance from the source to the reception point;
- the nature of the ground between the source and the reception point;
- the angle of view of the traffic stream from the reception point;
- the presence of screening (by fences, earth mounds, barriers or buildings), and
- meteorological effects, particularly wind strength and direction.
With the exception of the meteorological effects (refer Section 5.4.4), attention can be paid to all of the above factors in order to reduce the impacts of road traffic noise.
2.7NOISE DESCRIPTORS
There are two descriptors commonly used to describe road traffic noise which varies over time. These are L10 and Leq.
The noise descriptor L10 refers to the noise level which is exceeded for 10% of the time in a given measurement period, and corresponds to the average of the upper noise levels. In Figure 2.5 below, which shows typical noise level variations over a one hour measurement period, L10 is the noise level which is exceeded for 6 minutes (10% of one hour).
The noise descriptor Leq (the equivalent noise level) refers to the value of a steady noise that would have the same acoustic energy as the varying noise, over the same time period. Figure 2.5 below also shows the Leq level.
The descriptor L10 is used by some organisations as the descriptor for traffic noise. The descriptor Leq has now replaced L10 as the commonly used descriptor. Generally, L10 is around 3 dB higher than Leq, although this difference varies.
Figure 2.5 Common Road Traffic Noise Descriptors.
2.8NOISE MITIGATION MEASURES
There are several ways in which the impacts of road traffic noise can be reduced, the main ones being (also Refer Figure 2.6):