Project update

Update on the final sealing on CNC

We expect to apply the final chip seal and then low-noise asphalt layers on the CNC motorway starting in mid to late October, as soon as the weather is dry and the ground temperatures are warm enough. We will start our work on the motorway between QEII Drive and the Styx Bridge and we hope to have this section fully completed before Christmas. All the surfacing work for the entire motorway (Cranford Street to SH1) and QEII Drive between Main North Road and Innes Road roundabout will take until March 2022 to complete.  

The CNC Alliance has improved the design (recipe) for the final layer of asphalt to include epoxy which essentially makes the asphalt, more durable and longer lasting. We have decided to do this so the low noise surface will last longer and need less maintenance in the future. 

We will provide an update in October on work times and traffic management. For now we can say that we will be running the motorway with reduced lanes and speeds when we are sealing. After we lay the chip seal, there will be a low speed bedding-in period before the low noise asphalt can be laid on top.

Noise monitoring results on CNC

Following concerns from some nearby residents that noise from the new motorway was greater than they had expected, Waka Kotahi agreed to do further noise monitoring over a 24-hour period. This additional monitoring has been completed and we can now summarise and share the results with you.

• In most cases the noise levels measured over a continuous 24-hour period compared well with the shortened noise measurement process already reported for the CNC, and commonly used for sound monitoring. 
• Noise levels on the CNC will be at or below the NZ Standard for road noise, new and altered roads threshold of 57 dB LAeq(24hr), when future traffic increases and the low noise road surface are taken into account.

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.

Who to contact, frequently asked questions and videos

If you have questions about the CNC project, now or in the future, you can visit the project website nzta.govt.nz/cnc

Waka Kotahi will continue to manage this page and contact details will be updated on the site as needed.  You could also take a look at our Frequently Asked Questions webpage. Or your question could be answered in one of our Videos.

All the best

Melanie

More information

For more information on the Christchurch Northern Corridor project, visit our website www.nzta.govt.nz/CNC