Kia ora and welcome to an update from the Transmission Gully team.
It’s now been two weeks since the Transmission Gully motorway opened to traffic. We’ve heard lots of great feedback from people about the new road, and the difference a more reliable journey has made. More than 80% of vehicles are now using SH1 Transmission Gully rather than SH59.
We’ve now moved into the operations and maintenance phase of the Public Private Partnership contract. You’ll see the friendly Ventia team out and about monitoring the motorway. The team are based at the operations centre in Pāuatahanui, so they’re never too far away if someone needs assistance. They’ve already had some practice helping change flat tyres and clearing debris (things dropped off the back of vehicles) from the road in the first ten days after opening!
You may be aware that to enable the road to open sooner than would otherwise have been possible, Waka Kotahi deferred a number of the quality assurance tests that are required under the PPP contract. None of these deferred tests compromise public safety and we will be closely inspecting and monitoring the condition of the new motorway to ensure it remains safe for road users.
As well as completion of the remaining quality assurance tests, the road builder, CBP HEB JV, will also be working in a number of areas to fully complete the project. This means that you will see workers and construction vehicles around Transmission Gully for a while yet.
The remaining work includes finishing building the walking and cycling tracks and other off-road works, and completing the SH58 interchange. CPB HEB will also be doing further planting (once planting season starts again), and will complete the new section of SH59 between Paekākāriki and Mackays Crossing. The section of SH59 between Mungavin Ave and the Transmission Gully connection at Linden needs to be resurfaced too.
While there is still work to do, it’s a great time to look back at the enormous effort that has gone into transforming steep gullies of farmland and forest crisscrossed with streams into a modern motorway. This before and after video gives you a look into the transformation that has taken more than 12 million work hours to date!
On 30 March Prime Minister Rt Hon Jacinda Ardern officially opened the new motorway. The event started with a dawn ceremony with an ope from Ngāti Toa Rangatira travelling the length of Transmission Gully to carry out a karakia and blessing of the road before it was opened to the public. Once the karakia was completed, Ngāti Toa were joined by whānau from Te Āti Awa and Ngāti Raukawa to pōwhiri dignitaries and central and local government representatives to the opening event.
Watch the short video summary:
Once the official opening ceremony had taken place, it was all hands on deck as the team prepared to open the road to traffic. This short video shows some of work that took place late on 30 March and early on 31 March. You can hear the toots of excitement from the first vehicles to drive on the new motorway!
Construction of the new section of SH59 between Paekākāriki and Mackays Crossing isn’t yet complete. In the meantime, on-road cyclists are permitted to use a short section of Transmission Gully between Paekākāriki and Mackays Crossing to connect between the existing SH59 coastal route and the Kapiti Expressway.
Southbound cyclists must exit at Paekākāriki. We continue to encourage cyclists to use the shared path through Queen Elizabeth Park, Te Ara o Whareroa. This is the main route for cycling and was built prior to construction of Transmission Gully so that cyclists would have a safe alternative to SH1.
When you’re driving through Transmission Gully, you’ll see slopes with concrete ‘façades’ along your journey. This is shotcrete… and it serves a very important purpose.
Constructing the motorway through the challenging and steep terrain between Wellington and Kāpiti often meant cutting into the hillsides. During excavation, Geotechnical engineers assessed the strength and stability of the rock and its susceptibility to weathering every step of the way.
The Wellington region is riddled with fault lines, which fracture the rock and make it prone to instability and erosion. Combined with rock bolting and rock fall mesh, shotcrete was determined to be the best treatment to stabilise cuts and minimise erosion at a number of locations.
Designed to withstand a significant earthquake, the protective shotcrete plays a significant role in keeping motorists safe from rock fall.
The shotcrete used on Transmission Gully is not just concrete. It’s reinforced with steel fibres so that should an earthquake hit – the shotcrete will resist shaking from any direction, safeguarding against the slope crumbling down onto the motorway.
At each cut into the rock, Geotechnical engineers made assessments and advised the project team on the best solution for stabilisation. Shotcrete is always the final option of stabilisation utilised during construction. On some cuts, it was possible for vegetation alone to do the job. Other slopes required bolts to be drilled into the rock face, but many of the big steep cuts also required shotcrete to be applied.
The shotcrete is sprayed at high velocity through hoses (using compressed air) that look a bit like giant firefighting hoses. A concrete truck discharges the concrete into a pump hopper, which pumps the shotcrete through a 6cm diameter hose.
Given the mountainous terrain, it was a challenging job.
Up at Pouāwhā, the Wainui Saddle, some of the cuts are 70 metres high. The Ohariu Fault line runs right through the saddle. Here the shotcrete was applied from the top down, bench by bench.
While technical requirements take priority over cosmetics, designers still made every effort to improve the appearance of the shotcrete walls. The treatment was stained with five different colours to try and match the surrounding rock. The surface was shaped to make it neater, while the edges were feathered, and vegetation planted to soften the transition from shotcrete to natural environment.
Shotcrete is one of the reasons why Transmission Gully is such a resilient route. So, when you drive past those rather impressive grey walls, know that they’re helping to keep you safe on your journey.
When local iwi, Ngāti Toa, gifted the name Pouāwhā to the summit of Transmission Gully, it was with the weather firmly in mind.
Pouāwhā means ‘weather rod’ or weathervane…a very apt name for a place exposed to extremes of weather.
Meteorologist Lisa Murray from the MetService, says motorists need to be prepared for different weather conditions up at Pouāwhā, especially high winds, heavy rainfall and fog.
“We can expect that visibility on the motorway will be reduced in fog or low cloud, as motorists will basically be driving in the clouds at times. It’s pretty high at the summit - we’re talking twice the height of Ngauranga Gorge,” she says.
The Pouāwhā Wainui Saddle summit is 253 metres above sea level.
As the areas predominant North-westerly wind pushes onto our shores, the resistance of the land aligns the wind with The Transmission Gully motorway.
Lisa explains; “The steep cuts in the terrain, which are up to 70 metres high will help funnel the wind, increasing wind speed and gusts.”
The higher up you go the colder it gets, so there’s also the potential for areas of ice and frosts on still nights when temperatures drop below zero degrees.
All of this make it an exciting location for a weather station, says Lisa.
“It is really useful to have a weather station which sends us data from the most exposed place on the motorway. A high spec station up there means the MetService forecasters can trust the observations and can keep a close eye on the weather affecting the road.”
Then, there’s rain.
When a Southerly roars through Cook Straight and hits a North-westerly – it forces the air up and can cause persistent heavy rain or even thunderstorms. Three or four times a year these storms stall over the region and have a big impact on Wellington roads. Even one of those local thunderstorms over the Saddle, could mean heavy rain up to 25 millimetres in an hour or more.
It’s not hard to imagine why constructing a motorway through the Saddle was such a challenging engineering accomplishment. Carving the deep cuts into the terrain from the top down through a known fault-line meant the earthworks were high risk, made even more difficult by the effects of the weather.
The MetService already monitors State Highways and provides Waka Kotahi NZ Transport Agency with early warning of big weather events and advice about the day-to-day weather across their network.
In Transmission Gully’s case, weather warnings will also go straight to Ventia, the company which is operating and maintaining the motorway for the next 25 years.
Lisa says; “There will be times when there is significant weather on this road, but motorists should be reassured that MetService will be monitoring it – and will inform you through our National Warning Service.”
That’s thanks to the state-of-the-art weather station, which will be watched by forecasters and the motorway’s real time operators alike, 24 hours a day, seven days a week.
The station has numerous sensors, measuring temperature, wind speed and direction, humidity, rainfall, visibility, atmospheric pressure and solar radiation.
Motorists will be warned about conditions on Transmission Gully via bright Variable Message Signs (VMS). The public can also receive weather watches and warnings on the MetService website and app.
Meteorologist Lisa Murray says the weather station at Pouāwhā will also play a wider role in helping MetService verify weather extremes in the Wellington region. “When our forecast says; ‘gusts in exposed places’, this will be one of those exposed places.”
In addition to the weather station at Pouāwhā, the Wainui Saddle, Ventia have four airport grade visibility sensors that monitor fog or mist along the route.
Another road which is significantly impacted by Wellington weather is the Remutaka Hill road. With a summit twice the height of the Wainui Saddle, the Remutaka Hill is often subject to high wind or ice warnings and tends to be closed a few times a year due to extreme weather.
Fortunately, New Zealand motorists are used to extreme weather, and can be assured that the conditions on the motorway are being monitored and they’ll be kept informed.
The Transmission Gully motorway has been built to the highest specifications to ensure motorists have a safe journey, whatever the weather.
There are four new interchanges: Paekākāriki, State Highway 58 (SH58) at Pāuatahanui, Waitangirua and Kenepuru.
It’s important to know the Paekākāriki and Kenepuru interchanges don’t have ramps in all directions - so your journey to Wellington might be a bit different to your journey home. Details about the four new interchanges are below.
Travelling south from Kāpiti
The new motorway connects directly to the Kāpiti Expressway just north of the Mackays Crossing interchange.
If you’re travelling south from Kāpiti, and don’t want to continue on SH1 through Transmission Gully, you’ll need to exit at the Paekākāriki off-ramps. This will connect you with SH59 (the renumbered coastal route) which passes through Paekākāriki, Pukerua Bay and Plimmerton.
But be aware, if you miss the southbound exit at Paekākāriki, the next opportunity to turn off the new motorway is 15km away, at the SH58 Interchange at Pāuatahanui.
Travelling north from Wellington
The new motorway connects directly with the Johnsonville-Porirua Motorway.
When travelling north on SH1 and approaching the Transmission Gully connection at Linden, you should take the left or centre lanes to continue on SH1 via the new motorway. This is the best route if you are travelling to Whitby, Waitangirua, Pāuatahanui, Hutt Valley (via SH58) or Kāpiti.
If you’re travelling to Porirua City Centre or further on towards Paremata, Plimmerton, or Pukerua Bay, you’ll need to be in the centre or right lanes to continue on SH59 (the renumbered coastal route).
With northbound on and southbound off-ramps, this will be the main interchange for motorists travelling between Kāpiti and Paekākāriki, Pukerua Bay or Plimmerton.
This is also the last southbound exit on the new motorway for 15km,
Motorists travelling northbound on Transmission Gully (such as from Wellington) to Paekākāriki, should take the northbound off-ramp at Mackays Crossing and then travel south to this interchange.
State Highway 58 (SH58) at Pāuatahanui
The new interchange at Pāuatahanui connects the new motorway via SH58 to the Hutt Valley in the east and Paremata in the west, around the Pāuatahanui Inlet.
Motorists travelling from Kāpiti or Porirua to the Hutt Valley will be able to use this interchange to connect with SH58. It connects the new motorway (via SH58) to the Hutt Valley in the east and Paremata in the west, around the Pāuatahanui Inlet.
The Waitangirua Interchange connects the communities of Whitby and Waitangirua with the motorway, via two new Porirua City Council link roads.
You can get on or off Transmission Gully in either direction using this interchange.
To access Transmission Gully from Whitby, you’ll use Te Ara Kāpehu from the roundabout at the intersection of James Cook Drive and Navigation Drive. From Waitangirua, you’ll use the Waitangirua Link Road from the intersection of Niagara Street and Warspite Avenue.
The Kenepuru Interchange connects Porirua city centre and Tawa with the Transmission Gully motorway, via a new link road which crosses the existing SH1 and North Island Main Trunk railway line at Kenepuru.
Motorists travelling from Porirua city centre or Tawa, will be able to access the new motorway in both directions, via Kenepuru Drive. But motorists travelling northbound from Wellington to Porirua city centre, should continue to use their previous route – such as the off-ramp at Mungavin Avenue.
Motorists travelling south (eg from Kāpiti or SH58) will be able to exit the motorway at the Kenepuru Interchange.
As with any State Highway around New Zealand, you’ll be notified if there is any maintenance work scheduled that could impact on you. You can contact the Transmission Gully team via the 0800 TGINFO (0800 84 4636) if you have any questions or concerns about maintenance work.
If you have any questions, please contact us at email@example.com. If you have an urgent matter, please call the 24-hour project hotline on 0800 TGINFO.
But for now, Haere rā from the Transmission Gully team.
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