Noise management

Noise management

•   What are the sources of road-traffic noise?

  Many people notice road-traffic noise after a new road is constructed or after an existing road is modified. Because the noise is new and different, it is potentially more annoying. 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 the Expressway
  • vehicle noise – engine/exhaust noise, rattling of vehicle bodies, noise of engine braking
  • bridge joints – can make a distinctive sound as vehicles pass over them.

  Traffic noise factsheet [PDF, 1.5 MB]

  Close

•   How is noise measured?

  Noise levels are expressed in units of decibels (dB), which are a measure of the air pressure change caused by sound. 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. This adjustment is called “A weighting” and is identified by the letter “A”. Noise level measurements for the Expressway project are ‘A-weighted.’

  Traffic noise levels fluctuate so they are reported as an average value over a period of time. In New Zealand the period of time 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 on an energy basis. You can think of this averaging as one where louder noises have a disproportionate effect on the average. For example, the average of 40 dB and 60 dB both measured over the same time period is approximately 57 dB (not 50 dB, as with simple averaging).

  In Expressway project information you may see sound levels reported in units of “dBL_{Aeq (24h)} “ – this is an abbreviation of the 24-hour continuous sound level equivalent in “A-weighted” decibels (colloquially referred to as the 24-hour average).

  Close

•   What is the Transport Agency doing about engine braking noise from the Expressway?

  Disturbance caused by engine braking is often caused by a small number of vehicle operators. The Transport Agency has found liaising with individual operators is the most effective way to manage engine braking noise disturbance.

  The Transport Agency has installed five monitors to detect engine braking noise and identify individual vehicles.

  The information gathered from these detectors will help us as we work with the trucking industry and individual drivers to limit engine braking in built-up areas along the Expressway.

  The use of the engine braking detectors elsewhere in New Zealand has shown that loud noise from engine braking is not as frequent as objectionable noise from other vehicles (such as motorcycles, modified cars and sirens), or other heavy vehicle noise.

  • Heavy vehicle noise [PDF, 68 KB]

  Close

•   Why hasn’t the Transport Agency installed signs restricting or prohibiting engine braking along the Expressway?

  The Land Transport Management Act limits the Transport Agency’s authority to enact a bylaw prohibiting or restricting engine-braking to roads where the speed limit is 70 km/h or greater. This is because engine brakes are important supplementary safety device for slowing vehicles down in some situations, for example on higher speed roads, such as the Expressway.

  The Transport Agency has installed permanent advisory engine braking signs along the Expressway to ask heavy vehicle operators to limit their use of engine brakes.

  Close

•   How did you decide what noise mitigation to build on the expressway?

  During the consenting phase of the project an assessment of road-traffic noise effects was prepared. This assessment considered the effect of estimated noise levels at existing houses located within approximately 100m of the Expressway.

  The predicted noise levels were estimated utilising a computer model based on future traffic conditions (for the year 2026). The predicted noise levels were compared against the criteria in the New Zealand Standard (NZS 6806).

  In areas where road-traffic noise levels at houses were predicted to exceed the criteria in the New Zealand Standard, a series of options were developed for noise mitigation. These options typically included low-noise surfacing and/or noise barriers or bunds of varying heights and locations.

  A group of subject matter experts then completed a Multi-Criteria Assessment (MCA) of the mitigation options, and selected the ‘best practicable option’ for noise mitigation. These experts considered the acoustic benefit of the options and weighed those up against other factors, such as feasibility, urban design, landscape/visual, safety, storm water, environmental and cost.

  The selected mitigation options and decision-making process is documented in the noise assessment report. Together, these were included as part of the supporting information for the Board of Inquiry, and implementation of the selected mitigation is specifically required as part of the project statutory approvals.

  In summary, the decision-making process around noise mitigation considered the future road-traffic noise levels at individual houses located adjacent to the Expressway and the benefit that the noise mitigation would provide, weighed up against the other factors described above to select the ‘best practicable option.’

  Close

•   Who determines whether the Transport Agency is complying with the noise requirements for the Expressway?

  The final determination as to whether the Transport Agency has complied with its resource consent conditions is the responsibility of the Kāpiti Coast District Council as the consenting authority.

  There are two main steps to confirm that the Transport Agency is complying with the noise requirements for the Expressway:

  1. Confirmation that noise mitigation was implemented in accordance with the project noise mitigation plan.
     
     • This step is complete; an independent report prepared by Opus Consultants indicates compliance with the noise mitigation plan.
  2. Verification that the computer model used to assess noise exposure and select the appropriate mitigation were sufficiently accurate to meet the requirements of the project’s statutory approvals. The conditions require that the noise monitoring to verify the model predictions takes place in approximately two years after opening of the expressway.

  Close

•   Will the Transport Agency compensate me for the perceived loss of value of my house due to its closeness to the Expressway?

  Where the Transport Agency acquired property, including parts of property, under the Public Works Act (the Act), compensation was provided in accordance with the Act, through the process administered by Land Information New Zealand (LINZ).

  Where properties are adjacent to the expressway but no portion of the property was acquired by the Transport Agency, there is no entitlement to compensation for perceived or actual loss in property value under the Act. Therefore, the Transport Agency does not provide compensation in such situations.

  Close

•   Why aren’t the noise level criteria lower at night when most people are sleeping?

  The level of noise from a road varies over a day depending on things like traffic volume and speed, the mix of individual vehicles on the road (eg, passenger cars and heavy vehicles), as well as the weather conditions and temperature.

  Average noise levels will most likely be highest during commute hours and during the day, when traffic volumes are also highest. Average noise levels from the expressway will reduce over the night and gradually increase again from early morning to the peak morning commute period.

  Noise from individual vehicles does not change throughout the day so everything else being equal, the noise from an individual heavy vehicle or car passing at night or in the day remains the same.

  Outside noise is typically lower at night and as most people also sleep this is when noise is often most disturbing. Some countries have separate criteria for road-traffic noise to address increased sensitivity to noise at night. In New Zealand, the previous “Transit Guidelines” and the current New Zealand Standard use a noise level averaged over a 24-hour period.

  The criteria is based on people’s response to ‘real life’ traffic noise over a 24-hour period, including exposure to noise at night and exposure to individually noisy vehicles. The studies supporting the response to noise are population-based rather than individually-based, and consider annoyance, disturbance and health impacts associated with exposure to road-traffic noise over years.

  So while the New Zealand Standard only provides criteria for noise averaged over 24 hours, those criteria were developed based on people’s response to real-life traffic, including noise at night. The noise metrics tool demonstrates how various noise metrics are incorporated in to the 24-hour average.

  During development of the New Zealand Standard, separate day-night criteria were considered. The committee that developed the standard undertook a review of a number of existing roads in New Zealand, and looked at scenarios where 24-hour criteria were applied versus separate day/night criteria. This review concluded that similar noise mitigation requirements were likely regardless of the choice of whether day/night or a 24-hour average criteria were applied.

  On the basis of this assessment, and the understanding that the 24-hour criteria included people’s response to noise during the night, the committee adopted a 24-hour averaging period for the noise criteria in order to simplify application of the criteria.

  Noise metrics tool
  Fundamentals of sound

  Close

•   What is the New Zealand Standard 6808:2010 and how was it developed?

  NZS 68062010 Acoustics – Road traffic noise – New and altered roads sets out procedures and requirements for the prediction, measurement, and assessment of road traffic noise for new and substantially altered state highways and local roads. It 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 taking into account 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 that developed the Standard, was made up of representatives from a wide range of organisations that include 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.

  NZS 6808:2010 Acoustics – Road traffic noise

  Close

•   If I don’t think the NZ Standard 6806:2010 has adequately met the health and wellbeing needs of adjacent residents, how can I seek to change this standard?

  Enquiries or comments about the Standard may be emailed to: enquiries@standards.govt.nz

  Close