While a lot of attention has been directed at Wellington's Transmission Gully construction, another major roading project has been quietly taking shape north of the capital.
Construction of the Peka Peka to Ōtaki Expressway (PP2Ō) is in full flight with a lot of visible progress.
A flight over it with Kapiti Heliworx really highlights the amount of work undertaken already.
It's a hive of activity with about 280 staff on average working on the roading project.
"As the project progresses, the number of people working on the main elements of the project, such as structures, drainage, earthworks and pavement, varies," Waka Kotahi NZ Transport Agency project delivery senior manager Andrew Thackway said.
"As the project is now entering a different stage of construction, there will be more people working on drainage, pavement and landscaping, while the number of people required for earthworks and structural works will reduce."
Construction of the 13km four lane PP2Ō, spearheaded by Fletcher Construction, started in November 2017 with an original completion date of January 2021.
But the finish date has been pushed out, to a date not yet confirmed, because of the additional requirements of building a 10km shared path (for cyclists, pedestrians and horse riders) alongside the expressway, upgrading the surface of the expressway with a new pavement design and of course the impacts of Covid-19 lockdown.
It has also meant an increase in cost from the original estimated $330 million to the current construction estimate of $405m.
One of the new costs has been the decision to change to a new pavement design after surface issues with the neighbouring Mackays to Peka Peka Expressway (M2PP).
"The pavement for PP2Ō will be a deep lift structural asphalt with an epoxy modified open-graded porous asphalt surfacing," Thackway said.
"This pavement is a similar pavement design to the remedial pavement that is currently being constructed at M2PP.
"The deep lift pavement is a significantly more durable and robust pavement compared to the original granular pavement constructed at M2PP."
The overall expressway build is well advanced with 85 per cent of the bridges completed. Nine of the 10 major bridge structures have been substantially completed.
Three of them have been opened to traffic and another six are close to completion [over 85 per cent].
And the last one, the Marycrest rail overpass, is just over 30 per cent complete.
Earthworks are 80 per cent complete and progressing well, drainage and pavements are 50 per cent complete, local roads 5 per cent complete (main alignment), and planting is 30 per cent complete.
The largest bridge project was creating a new one over the Ōtaki River.
The bridge is 333m long, includes 10 spans of 11 Super T beams, and when complete it will have used over 10,000m3 (four Olympic swimming pools) of structural concrete.
And more than 1200 tonnes of steel reinforcing has been used in the concrete.
Understandably a bridge this size has presented engineering challenges.
"For example, as the concrete and steel within the bridge heats up over the course of a day, the bridge can expand in length by more than 40mm," Thackway said.
"To deal with this, the bridge is not connected to the abutment, but instead, there is a 230mm gap at each end, which is covered by an expansion joint.
"The Ōtaki River is also one of New Zealand's fastest-rising rivers, which presented a challenge during the construction of the bridge piles.
"Warnings about rising river levels meant that the team had to be vigilant and able to adapt quickly.
"An agile system of working was introduced so that the team could quickly and easily pause work and evacuate the site (people and equipment) before river levels started to rise above safe levels."
It is expected construction traffic will be able to drive across the bridge early next year.
Other key project challenges had included careful environmental management, including translocation of fauna, due to the number of watercourses in the area and the need for temporary diversion while bridges and culverts are constructed.
There had been geotechnical challenges due the presence of deep-seated peat veins.
Availability of quality earthworks material for construction of the expressway meant two off-line borrow sites have had to be established to provide appropriate construction material and dispose of unsuitable material.
Extra care was needed creating the expressway through the middle of an operational quarry.
And flood modelling and management in such a flat catchment was very important.
Other key features that have had a lot of time devoted to them have included working with the community to keep them up to date on progress and manage expectations.
"Ōtaki is also a unique community with strong Māori heritage," Thackway said.
"Around 17 per cent of the population speak te reo Māori, compared with around 4 per cent nationally.
"In recognition of this, bilingual safety signs were prepared for the site, which resulted in an award for the project."
The area is also culturally significant for local iwi.
"A significant kōiwi find in 2019 (around 16 bodies) involved careful exhumation and reinterment while working closely with local iwi."
There had also been the relocation of 1.3km of the North Island main trunk railway, relocation and restoration of heritage structures including Clifden Cottage and the Mirek Smisek pottery kilns, and design/build sculptures that will signify the entry points to Ōtaki to encourage visitors to the township.
The project has also provided opportunities for local people to access Fletcher Construction's apprenticeship programme and joint initiatives with Ōtaki College (Careers Expo day, horticulture and digital media programmes, and student work experience).
"One student has gained employment at Fletcher Construction as a result of the Careers Expo day.
"We are also working closely with Ōtaki College to identify other opportunities through the project for students.
"For example, PP2Ō has an arrangement with the school to provide videos — shot and edited by students — for our project updates.
"We also sponsor the college's Evelocity team, which designs, builds and races electric vehicles against other schools — taking out the top prize twice.
"We are proud to support these efforts which encourage innovation and give insights into engineering."
PP2Ō facts and figures:
· 13km, four-lane expressway
· 9km of new local roads
· 10km shared path
· 10 bridges
· 1.3km of railway track re-aligned
· 1.5 million cubic metres of earthworks
Key companies/organisations working on PP2Ō:
Fletcher Construction Company is the design and construction contractor. Nominated subcontractors include Beca (lead designer), Tonkin & Taylor (designer), Goodmans Contractors Ltd (earth moving), Higgins (pavement).
Waka Kotahi has engaged WSP New Zealand Ltd to fulfil the principal adviser and engineer to contract roles.
Ngā Hapū o Ōtaki and Muaūpoko Tribal Authority are Waka Kotahi's crown iwi partners. Kāpiti Coast District Council is a main partner on this project, as both the consenting authority and asset owners of the new local roads.
Greater Wellington Regional Council is a key partner from a flood management perspective.
The PP2Ō project has been working closely with KiwiRail on the rail track realignment north of Ōtaki Railway Station and Marycrest signalised level crossing.
Heritage NZ plays a key role in terms of the heritage and cultural aspects of the project. The project is also working closely with the Mirek Smisek Ceramic Arts Trust on the removal and reconstruction of the historic kilns.