A new Standard for measuring, predicting, assessing and, where required, determining appropriate mitigation for road-traffic noise was published by Standards New Zealand on 30 April 2010.

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Introduction

A new Standard for measuring, predicting, assessing and, where required, determining appropriate mitigation for road-traffic noise was published by Standards New Zealand on 30 April 2010. This Standard is referred to as ‘NZS 6806’ and its full title is: NZS 6806:2010 Acoustics – Road-traffic noise – New and altered roads.

Road-traffic noise from state highways has previously been assessed using the ‘Transit Guidelines’ from Appendix 6 of the NZ Transport Agency (NZTA) Planning Policy Manual. One of the weaknesses of the Transit Guidelines is that they often lead to noise mitigation solutions to achieve perfect compliance with noise limits, at the expense of integrated design and value-for-money. In some instances this has resulted in poor visual and urban design outcomes, and construction of substantial barriers for the sake of 1 dB attenuation

The NZTA Value Assurance Committee has provisionally adopted NZS 6806 for all new and altered state highway projects. With immediate effect, NZS 6806 is to be used in place of the Transit Guidelines. This decision is subject to review following further verification that value-for-money solutions do result from NZS 6806 when tested against an extended range of projects.

The assessment method in NZS 6806 requires consideration of a number of noise mitigation options depending on the scale of a project. For a transitional period of two years, the NZTA requires that assessments using NZS 6806 include consideration of a noise mitigation option complying with the Transit Guidelines.

Criteria

Unlike the Transit Guidelines, NZS 6806 does not set rigid noise limits. It gives categories (A, B and C) of noise criteria, and requires that the Best Practicable Option (BPO) be identified to mitigate road-traffic noise. This process promotes integrated design encompassing a wide range of factors as well as noise levels. The upper category (C) provides a backstop against adverse health effects such as sleep disturbance, by requiring insulation of houses if the external noise would not be sufficiently reduced using the BPO.

Use of the new criteria in NZS 6806 to date has shown:

• Costs for new roads in urban areas are generally less than Transit Guidelines, and
• Depending on the BPO, costs for major alterations to existing roads (altered roads) in urban areas may be more than Transit Guidelines.

Application

NZS 6806 applies to new and altered roads. It does not apply to existing roads, which are not being ‘altered’. There is a detailed definition of what constitutes an altered road within NZS 6806, and an online screening tool to assist in determining whether or not NZS 6806 applies to a particular project is provided this website. Maintenance works such as resurfacing are not classified as an altered road project.

Terminology

NZS 6806 introduces several new terms. Many of these have complex definitions, for which reference to the Standard is essential. These include: altered road, building–modification mitigation, cluster, design year, do-nothing, do-minimum, protected premises and facilities, structural mitigation, and rural/urban environments.

One of the key terms introduced is ‘protected premises and facilities’ (PPFs), which are the locations where road-traffic noise is assessed and for which noise mitigation measures may be required. These include residential buildings, marae, and teaching areas, although there are detailed inclusions and exclusions specified in the Standard. Only buildings within 100 metres of a new or altered road can be considered as PPFs in an urban area, and only those within 200 metres in a rural area. Urban and rural areas are determined by reference to the definition used by Statistics New Zealand, and can be seen on the NZTA Spatial Viewer.

Acoustics units

Road-traffic noise levels under NZS 6806 are measured in decibels (dB) as the A-frequency-weighted, time-average level over a twenty-four hour period (L_Aeq(24h)). This is the same unit as the Transit Guidelines.

However, the assessment position has changed. Under the Transit Guidelines, road-traffic noise is assessed outside at one metre in front of a building including noise reflected from the building itself (a façade level). Under NZS 6806 road-traffic noise is now assessed at the position of the building façade excluding noise reflected from the building, as if it wasn’t there (a free-field level). A free-field level (NZS 6806) is approximately 2.5 dB less than a façade level (Transit Guidelines). To provide consistency within future assessments, the noise limits from the Transit Guidelines will be reduced by 2.5 dB so that they can then be applied directly to free-field levels under NZS 6806.

Further information

In August 2010 the NZTA will be running a series of workshops about NZS 6806, around the country, for staff and contractors.

As well as the altered road screening tool mentioned above, this website will soon provide a template for calculating benefit-cost ratios and other guidance for applying NZS 6806.

NZS 6806 is available from Standards New Zealand, www.standards.co.nz.

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