We expect these noise levels to drop by at least 5dB when the final asphalt surface is laid on the CNC later this year. In general, people can hear a noticeable difference in sound levels with changes over 3dB.
As well as the low noise asphalt, we have constructed noise reducing earth bunds, wooden fences and concrete barriers in areas near residents living along the CNC. The noise modelling has shown us that these mitigations are working as we expected.
As part of this noise monitoring, we also asked our independent acoustic experts to monitor noise on other high trafficked main roads and a suburban road in Christchurch to provide some comparison. Results in these areas were as follows:
69dB on Christchurch Southern Motorway (near Wigram subdivision)
68dB on Yaldhurst Road
67dB on Memorial Avenue
52dB in Selwyn Street.
This showed us that current noise levels on the CNC compared well with the noise levels for other roads in Christchurch.
The CNC Alliance and Waka Kotahi aim to be good neighbours, and we take our social and environmental responsibility seriously. We recognise that transport noise can cause a range of impacts on people and communities, which is why we have considered suitable mitigations for the CNC project from preliminary design right through to post construction. We are aiming to lay the low noise asphalt later this year.