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Describes the sources and impacts of road traffic noise, how noise is measured, the factors that influence noise levels, noise standards and criteria, and how road traffic noise is managed for both new and existing state highways.

  • What are the sources of road-traffic noise?

    Sounds you may hear include:

    • tyre noise (or road-surface noise) – noise created when the tyre meets the road surface (over the course of a day this will be the dominant source of noise from a motorway)
    • vehicle noise – engine/exhaust noise, rattling of vehicle bodies, noise of engine braking
    • aerodynamic noise - noise created by turbulence around a vehicle as it passes through the air
    • rumble strips – vehicles travelling over rumble strips can make a distinctive sound
    • bridge joints – vehicles passing over them can make a distinctive sound. 

    At higher speeds (generally above 50 km/h) the dominant noise source from traffic is typically tyre or road-surface noise.  At speeds lower than 50km/h, vehicle noise typically dominates the noise environment over the course of a day. 

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  • What affects the level of road-traffic noise?

    Traffic noise levels are influenced by a variety of factors, including: 

    • traffic volume
    • traffic speed
    • number of heavy vehicles/trucks
    • driver behaviour
    • road-surface type and condition
    • noise barriers (bunds/walls)
    • screening
    • distance from road
    • weather (wind/temperature inversion).
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  • How is noise measured?

    Sound sources cause changes in air pressure which are detected by our ears. These changes in pressure can be measured by a sound level meter. The pressure changes are expressed in decibels, which is written as 'dB'.

    Measured noise levels include all frequencies, but as our hearing is less sensitive to lower frequencies, the measured levels are adjusted to correspond to human hearing. For most environmental noise, including road-traffic noise, an ‘A weighting’ adjustment is applied (identified by the letter ‘A’ , for example dBA or dBLA). 

    Traffic noise levels fluctuate so they are reported as an average value over a period. In New Zealand the period for which the average is calculated is 24 hours.

    Because decibels are a logarithmic unit, they cannot be averaged like normal numbers. Instead, the average is determined from the ‘energy levels’ and reported as an ‘equivalent’ noise level. You can think of this averaging as one where a louder noise has a disproportionate effect on the average. For example, the average of 40 dB and 60 dB both measured over the same time is approximately 57 dB (not 50 dB, as with simple averaging).

    In project information you may see sound levels reported in units of ‘dB LAeq(24h)’ – this is an abbreviation of the 24-hour continuous sound level equivalent in ‘A-weighted’ decibels (often referred to as the 24-hour average).

    Further information:

    Traffic noise [PDF, 1.5 MB]

    Noise metrics tool

    Fundamentals of sound

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  • What are the effects of noise on people?

    Exposure to high levels of environmental noise has been linked to cardiovascular disease, cognitive impairment in children, sleep disturbance, tinnitus and annoyance. Sleep disturbance and annoyance - mostly related to road traffic noise - constitute the bulk of these effects. 

    Noise may also reduce enjoyment of outdoor areas such as gardens, decks and play areas. 

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  • What are the noise limits for an existing road?

    In New Zealand, there are no national environmental or planning standards related to noise from existing roads. 

    However, both the Health Act and the Resource Management Act empower local authorities (councils) to regulate noise which may be unreasonable or injurious to health, through district plan requirements and resource consent conditions. 

    There are no numerical noise-level requirements or criteria in the Resource Management Act or the Health Act.

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  • Is there a New Zealand noise standard?

    There are no national environmental or planning standards related to noise.  However, there is New Zealand Standard (NZS) 6806 for the assessment of noise and noise mitigation for new and altered roads. New Zealand Standards are not a legal requirement unless required by statutory approvals or incorporated by reference in regulations, statutes or district plans.

    NZS 6806 sets out procedures and requirements for the prediction, measurement, and assessment of road traffic noise for new and materially altered state highways and local roads. The standard also provides best practice guidance and advice on methods for mitigating reverse sensitivity situations and the environmental effects of noise exposure on nearby noise-sensitive activities.

    The standard was developed considering health issues associated with noise, the effects of noise levels on people and communities, affordability considerations and the potential benefits of roads to people and communities. The standard recognises (as does the World Health Organisation) ‘that the evaluation of control options must take account of technical, financial, social, health and environmental factors’.

    The committee which developed the standard included representatives from a wide range of organisations such as Local Government New Zealand, Ministry of Health, Ministry of Transport, New Zealand Transport Agency, Road Controlling Authorities NZ, Department of Building and Housing, NZ Acoustical Society, NZ Institute of Environmental Health, Roading NZ, and Ingenium.

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  • When does NZS6806 apply?

    NZS6806 applies to ‘new’ and ‘altered’ roads and may be a requirement of project statutory approvals (eg resource consent or designation conditions). NZS6806 does not apply to existing roads. 

    The definition of an ‘altered road’ under NZS6806 is limited to changes in the road vertical or horizontal alignment that result in a significant change in average noise over the course of a day at nearby noise-sensitive receivers (such as a dwelling). The definition of an ‘altered’ road specifically excludes changes in road-surface or traffic volume, speed or composition (ie percentage of heavy vehicles).

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  • How is NZS6806 applied?

    NZS6806 sets noise criteria for new and altered roads to achieve reasonable noise levels at residential dwellings and other noise sensitive activities. NZS6806 is used to assess average traffic noise at residential dwellings close to the road (within 100m in urban areas and within 200m in rural areas) where noise effects are most likely to occur and to inform the best practicable option for noise mitigation.

    Noise mitigation is not required to be considered for properties beyond 200m (rural areas) and beyond 100m (urban areas) under NZS6806:2010. This is because noise reduces with distance from the road, and also because there is often screening from the road at those distances by either the land form or other dwellings/structures. In addition, noise barriers and/or low noise surfacing provided for houses closer to the road will also generally benefit those farther away.

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  • How does the Transport Agency manage noise?

    Road traffic noise from existing state highways is managed through ongoing good practice road maintenance and improvement activities to provide a smooth surface, for example, repair of road defects (potholes, ruts, etc) and planned resurfacing.

    There is currently no Government funding for retrospective mitigation of noise from existing state highways, for example through installing noise barriers or low-noise surfacing. 

    More information:

    • Refer to Loud vehicle and Engine braking questions and answers for management of noise from individual vehicles.
    • Refer to Reverse sensitivity questions and answers for management of noise from existing state highways in relation to proposed new development.
    • Refer to How is NZS6806 applied for management of noise from new or altered roads.
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  • Noise from the road seems to have become louder. Why is that?

    Many people notice road-traffic noise after a new road is constructed or after an existing road is modified. In some cases, you might be more likely to notice road-traffic noise after road works or maintenance activities because your attention has been drawn to the road rather than there being an actual significant increase in noise. 

    A common example of this is removal of roadside vegetation where the road then becomes visible or partly visible.  In most cases, removal of roadside vegetation will not cause a material increase in measured noise although it can increase perceived noise. 

    When windows are open for ventilation this may increase indoor noise from outside sources.  This may be particularly noticeable in spring and in summer after the windows have been shut for several months at night during the cooler autumn and winter seasons.

    Other common sources of increases in road noise include: 

    • if resurfacing work has been undertaken on the road there may be a change in noise levels or noise character because the surface type has been changed (for instance changing from an asphalt to a chipseal surface) or because the new surface takes some time to ‘bed in’
    • traffic volume change or increase in the number of heavy vehicles such as for seasonal industries
    • development of a fault in the surface, such as a pothole causing tyre ‘thumping’ noise or vehicle body noise (such as a rattle from a vehicle tailgate)
    • meteorological factors eg wind can cause noise to travel further from the road in the downwind direction.
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  • Does vegetation reduce road noise?

    Trees, shrubs and other vegetation generally provide minimal benefit in terms of reducing noise levels. Vegetation may provide visual screening of the road, which can result in a perceived reduction in noise.

    You may perceive an increase in noise with vegetation removal if the road then becomes visible and your attention is now being drawn to the road traffic. In most cases, removal of roadside vegetation will not cause a material increase in measured noise although it can increase perceived noise.

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  • How does increased traffic volume impact noise?

    How increased traffic volume impact noise

    Increases in overall traffic volume or in the number of heavy vehicles will result in increased road-traffic noise. However, noise levels are not as sensitive to traffic volume as many people perceive. As a rule of thumb, a doubling of traffic volume will result in an increase of approximately 3 dB. 

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  • How does increased speed impact noise?

    How increased speed impact noise

    As illustrated in the figure above noise increases with vehicle speed.  This figure also shows that at speeds above approximately 50kmh that tyre noise becomes the dominant source of noise.  At speeds less than 50kmh both vehicle (engine) noise and tyre noise contribute to the noise heard from the road.

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