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State highways, noise and reverse sensitivity: what’s the buzz?

By Oscar Savage, Graduate Planner, Baseline Group | Jul 29, 2022

The expansion of Selwyn’s towns and economies requires access via state highways for efficient transport of people and goods. The importance of state highways and residential development can result in the two competing land uses in close proximity to one another, resulting in spill over effects of noise, vibration, and dust. In anticipation and response to this Waka Kotahi (NZTA) have actively been working with district plan updates to create legislative instruments designed to protect property owners from any unwelcome surprises.

Reverse sensitivity issues arise when a newly established land use generates complaints from an existing land use. For example, State Highway 1 heading south out of Rolleston was established before the subdivisions of west Rolleston were developed. If the property owners adjacent to the state highway were to complain about the effects of trucks on the state highway at night, this would generate a reverse sensitivity effect.

To protect property owners, Waka Kotahi adopts best practice guidelines for road traffic noise which dictate specifics of road surfacing, signage, and physical noise barriers. However, Waka Kotahi is only responsible for the effects up to the state highway designation area boundary, beyond this it is up to Councils to decide what is and isn’t acceptable.

A range of methods can be used to reduce the physical noise effects. In some area this may be a physical earth bund constructed between dwellings and the road reserve area. As Council’s don’t own this land, it is usually either a condition of subdivision consent with a consent notice on resulting titles that a bund be installed prior to constructing a dwelling, or council has to buy a sufficiently wide enough strip to install a bund. The latter option obviously comes at a cost to the wider ratepayers as part of council expenditure.

In other areas, council may impose a dwelling setback, to be setback from boundaries with road boundaries. The setback distance can vary with examples between 40 m and 100 m present across Canterbury. These have mixed effects for protecting land owners from the noise being generated from traffic, with the distance between a dwelling and the source of noise designed to reduce the actual noise heard. However, on cool crisp evenings, noise travels long distances and this measure is not always a fully protective measure. It also limits how a land owner can use their land, pushing residential dwellings to the rear of sites.

Another successful measure is to require bedrooms to be designed with additional acoustic noise insulation, and require dwellings to meet specific acoustic limits. Certifying this has been achieved often requires expert acoustic assessment and can add time delays and additional costs to a build, through both expert opinion and additional gib requirements. With national shortages of gib presently, this might not be a feasible solution.

Beyond the health effects of being exposed to prolonged noise generated from road noise, Waka Kotahi are aware of being a good neighbour, and ensuring the roading environment does not generate amenity effects for its neighbours Proximity to a road, and the reasons behind the planning framework that seeks to avoid reverse sensitivity effects is something worth considering when buying your next home.

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