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Kia ora and welcome to our Autumn 2021 update from the Transmission Gully team.

Kia ora

With less than six months to go till the Transmission Gully motorway opens to traffic, it’s full steam ahead onsite. Construction work on Transmission Gully is 92% complete and earthworks is now 99.6% complete.

Check out our latest fly through of the project (captured in February 2021) to see how far we’ve come.

You’ll see from the fly through the various stages of paving throughout the site, with many different layers of material going down to make the pavement. The team are 52% through the paving programme. The paving on Transmission Gully is made up of both granular pavements (with chip seal surfacing) and structural (deep lift) asphalt pavements. Take a look at how our structural asphalt pavement is made in the video below.

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New temporary asphalt plant at Lanes Flat

For the next three to four months, drivers along SH58 at Pāuatahanui may spot a new addition to the Transmission Gully site compound at Lanes Flat – a mobile asphalt plant.

Its purpose is to supply ‘deep lift’ asphalt to pave the steep incline near SH58 and other interchanges further south.

Located within an existing stores and stockpile yard opposite the Transmission Gully office, the temporary plant will generally operate from 7.30am till 5.30pm, six days a week. (There may be some variation in these hours, with operation from 7am till 10pm on a weekday and 6pm on weekends permitted within a 10 hours per day limit.)

Having an asphalt plant right on-site means the hot asphalt can be delivered quickly to where it’s needed on the new road with minimum disruption to the traveling public.

At just 33 metres long, the plant is compact enough to fit on the back of two truck trailers. In fact, it will remain on the trailers for the duration of its time at Lanes Flat. While small, this plant is capable of mixing asphalt up to 200 tonnes per hour which makes it one of the highest output plants in New Zealand.

Mobile asphalt plant being erected.

The mobile asphalt plant being assembled onsite at Lanes Flat, Pāuatahanui.

Mobile asphalt plant with an empty truck waiting to be filled.

The mobile asphalt plant in operation (photo taken at its last location on the Desert Road).

This plant is the most advanced and modern in New Zealand with class leading emissions and quality controls.

Locals may notice white steam coming from the plant while it’s operating. This is just moisture coming from the aggregate as it is heated and mixed with the bitumen to make asphalt. The operation passes all air discharge quality standards and we can assure you that there is no risk to public health.

Having a plant on-site has many benefits. It gives the project extra capacity and reliability and reduces the number of truck movements on the wider transport network. Previously the hot asphalt (needed for the Southern end of TG) came all the way from the Kiwi Point plant at Ngauranga Gorge – 22 kilometres away. The new temporary plant is only a few hundred metres from Transmission Gully.

There will be a localised increase in traffic volumes between the Pāuatahanui roundabout and the site access point at the Transmission Gully/SH58 interchange, but there will be an overall 15% reduction in truck traffic on SH58 west of Transmission Gully (Paremata to Pāuatahanui) with the establishment of an on-site plant, compared to asphalt being trucked into site from Kiwi Point.

The plant is operated by one of Transmission Gully’s paving sub-contractors, Downer.

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Southern connection at Linden

There has been some public discussion recently about how southbound Transmission Gully traffic will merge with traffic on the old SH1 (coastal route) or Linden.

Four-laned state highway with flyover bridge crossing over the existing State Highway 1.

The new Transmission Gully connections at Linden.

On the left of the above photo, northbound traffic on SH1 will either diverge left and drive up onto the overbridge to continue on the Transmission Gully motorway, which will become the new SH1 route, or diverge right and continue on the old SH1 to get to Porirua, Mana or Plimmerton. On the right, southbound traffic from Transmission Gully will merge with southbound traffic from the old SH1.

The way the southbound merge will work is that four lanes (two current SH1, two TG) will merge into three lanes. It will resemble the configuration at the bottom of Ngauranga where southbound SH1 and SH2 come together and the two ‘centre lanes’ gradually become one.

Then, several hundred metres further south, the southbound left lane will merge into the centre lane, so, three lanes become two.  It’s a little difficult to visualise this on the existing road layout as currently some of the lanes are unavailable while the median works are completed.

Waka Kotahi is working to prepare the wider State Highway network for the opening of Transmission Gully. This includes measures such as variable messaging signs (VMS) and additional CCTV cameras for traffic monitoring to improve the efficiency and safety of the merge point between Transmission Gully and the old SH1.

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Kenepuru Interchange works

Nightworks are underway on Kenepuru Drive in preparation for the construction of a new two-lane roundabout, part of the Transmission Gully project’s Kenepuru Interchange.

Once Transmission Gully opens, the Kenepuru Link Road will take traffic to and from the new motorway and will connect with Kenepuru Drive at the new roundabout, located near North City 10-Pin.

Map on the new roundabout at Kenepuru Interchange with cycle lanes and shared paths visible.

How the roundabout will work once completed.

Aerial view over new Kenepuru interchange with road still under construction.

Preparatory works are underway on the Kenepuru interchange.

We will maintain two lanes of traffic (one lane in each direction) through the worksite on Kenepuru Drive during the day. Please be aware that traffic will be under ‘stop/go’ traffic management at times during the night.

Bluff Road will need to close for 6–7 weeks from the end of April for stage 2 of the works, with no right turns in or out during other stages. No access is available by Lower Main Drive. A diversion will be available via Raiha Street and Hospital Drive.

Parking will also be removed in front of the Institute of Environmental Science and Research (ESR). The footpath on the western side of Kenepuru Drive will still be available to pedestrians, but it will be a congested work site, so caution is advised. 

Work is scheduled for completion in September.

To understand more about what the four stages of work will mean for road users, see the maps below.

Kenepuru Interchange stages of work

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Keeping you up to date

We continue to remind all members of the public to stay safe and not enter the project site at any time. Work is underway in multiple areas and it remains a high hazard area.

If you have any questions, please contact us at info@tg.co.nz. If you have an urgent matter, please call the 24-hour project hotline on 0800 TGINFO. If we are working outside of our normal work hours and you’re one of our neighbours, we’ll be in touch with you directly as usual.

In our next newsletter, we check out how concrete kerb and channels (a.k.a. gutters) are made using a Slipform machine.

But for now, haere ra from the Transmission Gully team.

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We hope you enjoy reading these updates, and we’d love to hear from you. If you have any questions, comments or story suggestions, you can email them to info@tg.co.nz

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Crew laying structural asphalt

The Fulton Hogan paving team laying structural asphalt south of Pouāwhā, the Wainui Saddle.

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