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$6 billion cost blowout prompts major changes to the Government's transport plans; Upgrades to Mill Road, SH1 between Whangarei and Port Marsden, and the Takitimu North project affected

$6 billion cost blowout prompts major changes to the Government's transport plans; Upgrades to Mill Road, SH1 between Whangarei and Port Marsden, and the Takitimu North project affected
Mill Road. Image from NZTA website.

The Government is pulling the pin on its commitments to upgrade both Mill Road in South Auckland and State Highway 1 between Whangarei and Port Marsden.

It is also halving the length of the planned expressway between Tauranga and Ōmokoroa, so it stops at Te Puna, rather than going all the way north to Ōmokoroa.

The Northern Pathway will no longer be connected to the Auckland Harbour Bridge, because the bridge can't handle this much additional weight. Rather, the Government has committed to building a separate structure alongside the bridge for walkers and cyclists.

This project is expected to take five years to complete and cost $785 million.

The changes come, as the Government reassesses its $6.8 billion New Zealand Upgrade Programme, unveiled in January 2020.

Six of the 32 projects included in the programme won’t go ahead as initially planned.

New cost estimates for all the promises made in January 2020 are expected to see the cost of the initial NZ Upgrade Programme almost double to $12.8 billion.

The now-scrapped Mill Road upgrade, for example, was priced at $1.85 billion last year, but is now expected to cost $3.5 billion. 

Finance Minister Grant Robertson attributed the cost blowout to increased construction costs globally due to COVID-19.

He has allocated an additional $1.9 billion towards the programme.

The projects that will be changed are among the more expensive ones.

Projects that will go ahead as planned include Ōtaki to north of Levin, Penlink, SH58, SH1/29 in the Waikato, Melling, Takitimu North Link Stage One, and the Canterbury and Queenstown transport packages.

Here are details of the changed projects, in the words of Waka Kotahi NZ Transport Agency:

Whangārei to Port Marsden Highway

Government has instructed Waka Kotahi to implement a new option that focuses on safety improvements along the existing state highway and a new rail line to Northport. The current proposal for a new state highway will not continue.

South Auckland projects

Government has increased the level of rail investment to allow construction of three new rail stations in addition to rail electrification and a third rail line. The new scope will deliver a two-lane northern section of Mill Road (Flat Bush to Alfriston), SH1 improvements, including a shared path between Papakura and Drury and investment in Drury transport upgrades that support releasing additional housing. The existing proposals for Mill Road and Papakura to Drury South Stage 2, including Drury South interchange, will not be progressed as part of the New Zealand Upgrade Programme.

Takitimu North Link

Takitimu North Link Stage 1 will start construction, subject to property negotiations, later this year. Route protection of Stage 2 will be delivered by the New Zealand Upgrade Programme, however further work beyond route protection, including construction, will require funding through the National Land Transport Programme. This won’t occur within the next three years and is unlikely to be within the next 10 years.

Transport Minister Michael Wood said, “Recognising the need to decarbonise our transport system, we’re rebalancing the package to increase investment in rail, public transport and walking and cycling. 

“If we had proceeded with Mill Road as originally scoped, it would have cost up to $3.5 billion and at peak produced six tonnes of CO2 emissions a day. Instead, we’ve focused on delivering important safety improvements to Mill Road, upgrades to SH1 and rail, and new rail stations connected to public transport, walking and cycling infrastructure. This rebalanced package helps manage debt, reduces emissions and supports housing growth.

“The Marsden Point rail spur will be a strategic investment in Northland’s future prosperity, getting heavy trucks off the road to make the highway safer, and reduce emissions. We know safety on SH1 is a concern for locals, so there will be targeted safety upgrades, including median barriers, along the route.

“Meeting our commitment to decarbonising transport means that we have to start doing things differently.

"This re-balanced NZUP package shows our intent, and to guide future investment I intend to amend the Government Policy Statement on land transport to provide Waka Kotahi with the clarity it needs to make investments consistent with our country’s decarbonisation goals."

National: Govt down-played costs ahead of the election

National's Infrastructure spokesperson Andrew Bayly coined the Government's cost blowout claim "the worst form of politics".

“The Government deliberately down-played the cost of the Upgrade Programme during an election year so New Zealanders rightly thought those projects would go ahead," Bayly said.

“Now that costs have predictably increased as a result of the Government’s three-and-a-half-year delay, it is cancelling much needed projects that it is ideologically opposed to, like Mill Road."

National's leader Judith Collins said: “The Government’s fixation on walking, cycling, and forcing people out of their cars is out of touch with modern New Zealand. Grant Robertson should try cycling across the harbour with groceries, sports gear and the kid’s netball team and see how that goes.”

National’s Transport spokesperson Michael Woodhouse said the new bridge next to the Auckland Harbour Bridge should have capacity for cars, freight and public transport to ensure it is future-proofed. 

“It’s unclear why Labour is opting for a piecemeal solution when we know the current bridge has serious structural issues," Woodhouse said.

“It’s clear Labour’s transport priorities are all wrong. If the second harbour crossing isn’t done properly then Aucklanders will be fighting gridlock for decades to come...

“Labour could do this now by ending its obsession with light rail down Dominion Road, which could cost upwards of $10 billion, and spend this money on high-priority projects."

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Silly Robertson. He should take his Reserve Bank Governor's advice and wait a bit. After all, inflation is only temporary.

"The Marsden Point rail spur will be a strategic investment in Northland’s future prosperity, getting heavy trucks off the road to make the highway safer, and reduce emissions"
I see this as a dog, the existing line to Auckland is a single track that goes via the West Coast, very indirect. Just what freight is suited to rail ? bulk stuff that can be stock piled ?
If containers come into Marsden Point it is almost all cargo that requires prompt deliverer that will still be trucked, just another con !

Why would you send something requiring prompt delivery via a container ship?

Do you not realize that around 1/2 of Auckland's containers come from Tauranga , by rail?
the Northland link is slow at the moment , but will be sped up by the time significant traffic is moving via North port.

Led by donkeys.


That's how inflation works. Unfortunately we really need to push ahead regardless, we don't have the luxury of slowing infrastructure investment when it is already at such low levels.


There is no inflation, because the CPI is below target. Any inflation that is occurring is just transitory and we need to "look through" it.

However the reserve bank is 'monitoring' the situation closely. Mighty Tane Mahuta will keep the financial stabilities of the asset prices up in the sky.

Grant shouldn't worry his pretty little chins about the buying power of his money. Mighty Tane Mahuta will ensure he has a "job" because wasting time on make-work and cultural appropriation are what really matters.

Guessing they didn't watch the Berkshire Hathaway meeting where Warren express concerns about the large inflation he was seeing. Inflation in the real world is quite large at the moment.

That's how incompetence works!

Count to a minimum, not including any additional costs.

Take the project through the politicians.

In the course of construction, increase the estimate by 5 times.

Redo everything on the go to pretend that it is possible to meet the new amount.

Find the flaws and double the estimate.


Isn't the underlying inflation issue just property speculation increasing the cost of buying properties over which the roads will be constructed?

not a lot for sure


As I have said before it was fortunate that National started the new motorway project north of Puhoi or else Labour would have canned it. I thought we were right into "Shovel Ready" projects right now ? This one looks like it needs a big shovel.

Yup i can't wait till it opens and i can get to whangerei in 2h53m instead of 2h57m. That's going to be a real gamechanger for the northland economy!

more roads - more motorists.

more railways - more commuters

But that's public transport's little secret. After spending billions on Auckland's passenger rail, use by commuters is going down. It was slipping before the pandemic (80,000 rides per day, say 40,000 people). After it is running -30% less (55,000 rides per day, say 27,500 people). And the voices are unchanged for more billions for passenger rail - into a system that is going backwards in terms of rider choice. Like cycling, it is no longer "mass transit" - it is just a subsidy for a few who need to go to Queen Street by the many (850,000+) who don't. We do need solutions, but not just for a few loud voices - for most people.

Yeah, National loves building roads that have very low to non-existent benefit-cost rations, and which will just increase our carbon emissions.

Thank goodness Melling interchange is going ahead as planned!

Had an interesting talk about rail the other day. Seems to me there's not so much a need for investment in rail as there is a need for change of attitude towards new customers with needs outside the current schedule. That is, a customer wanting to send whole trains to port, regularly, with easy access, gets a simple no doesn't fit us.

I can’t speak for them but they. Just ordered 1000 wagons and 400 engines, that may help a little.

There is no inflation but we have canned these projects because they became too expensive…


So important roading projects cancelled but a bicycle bridge will be built over Auckland harbour for $785million.

We are indeed living in a very strange world.


the cost vs. the planning, scale, quality, finish time of infrastructure projects in NZ is laughable.

What really happened is the dispatch guy in the structural steel factory got the address labels mixed up. The steel that went into those bridges was export grade.

Sorry, we need more Rich Tourists, not more permanent residents. The Capital Idea is what is needed, not more poor citizens wittering on about our lack of infrastructure.

(Tongue in cheek).

People travelling on bike and foot across the harbour are expected to make up roughly 1% of total commuters.

No way the analysts at NZTA could spin this in any way for the business case to make economic/financial sense. Perhaps hiring policy majors exclusively from Vic Uni for investment analysis could help work around this roadblock!


See my post below. I worked the 30 year cost as $4.40-odd based on 10,000 users. But they reckon only 1700 per day will use it? That's $26 per return trip over 30 years. Even spread over 50 years that's $15.63 per return trip!

This is so appalling.

But! It will reduce global carbon dioxide emissions by 0.0000563% so effectively if you don't build this bridge, you're condoning the burning of Orangutans.

I got the numbers wrong. The user numbers are expected to be way lower (1700 per day). Even over 50 years the cost works out to be $25 *per return trip*

Yeah, really should change the lane allocation on the existing harbour bridge to 2 lanes buses, 2 lanes cycling and walking, 4 lanes everyone else. And further upgrade the rail link to Northland to get trucks off the road (getting the Marsden Point port rail line is a great move).

And more people will travel in the 2 lanes buses and 2 lanes cycling and walking per day than would travel in the remaining 4 lanes.

People travelling on bike and foot across the harbour are expected to make up roughly 1% of total commuters.

No way the analysts at NZTA could spin this in any way for the business case to make economic/financial sense, unless such feasibility tests are absolutely blinded by ideology.

Can you imagine all these amazons, walkers, runners, and cyclists using the walkway on a shitty freezing cold day with driving rain and a 100 kph howling wind. You can lay odds they won't

Oh well $700 million to shut them up

Toughen up. Some of us have walked/ biked an entire life. It’s called adapting... man has done it successfully for thousands of years.

Hard to walk when your leg muscles have a degenerative disease and oh look the arm muscles can no longer work either. Do you have any of that magic fairy dust handy because without vehicle transport there is NO OTHER OPTION TO GET TO HOSPITALS, HOMES AND WORK. Vehicle transport allowed trades and logistics to allow for much larger populations without massive scales of death. Changes to transport are the leading cause of enabling the est lifespan to grow over the age of 50. But sure lets have more death of other people so long as it is not you right.

Nobody is trying to force everyone onto a bike. It won't work for people physically unable or those carrying lots of materials or more children than a cargo bike can handle.

However, most journeys are made by physically capable people using a half ton metal box just to carry themselves around. The bike bridge allows some of them to get off the roads and make space, while improving their health, finances, and the environment.

While I somewhat agree, it is sending the wrong message. They should simply use an existing lane on the bridge, cheaper and sends the right message - OUT OF CARS PEOPLE! It would have an induce demand effect for many people that I know of who cycle, they could get their exercise in their morning commute, rather than having to drive. Would actually be faster for most people as well.

I mean AHB is 8 lanes wide, during rush hour it's 6 lanes going in/out. That's so many lanes for huge useless metal boxes, it's not funny. Reduce it by one and turn into a cycle lane with good connections and you will see many a car driver make the change. The options will be: stuck in gridlock or: get into work quicker. Guarantee many will take the latter option as they often do everywhere else in the world where people are given the choice. With the popularity of e-bikes, the equation becomes even better.

Sounds good to me. I've never lived in Auckland so don't really know the local specifics, but it looks like a massive hole in cycling infrastructure at the moment so any way to fix that would be great. More people out getting exercise and reducing the amount of oil we need to bring into the country, and the fumes the rest of the population have to inhale.

"huge metal useless boxes" that are getting people to work, school, study etc. But sure, let's keep insisting that cars generate no useful utility and that everyone has the privileges afforded to inner-city white collar workers who want to cycle in when they feel like having a few after work on Friday. Meanwhile, in South and West Auckland, people who have to commute and can't set their own hours will just face longer and longer delays getting home to their families, while well-off inner North Shore residents get hundreds of millions of dollars thrown at them, on top of the bus way the Shore already had a decade before anyone else in Auckland.

They are useless because they are inefficient. Moving 1500kg just to take a 100kg person somewhere twice a day is huuuugely inefficient, a waste of fuel, time and publicly funded resources (a cars footprint on our infrastructure is massive). An ebike at 25kg to transport that same person is so much more efficient, it's not even worth comparing. Are you saying white collar workers that drive, drive back drunk on Friday's, but this would be a disaster if they were on a bike rather than a car???

Your other argument that South Auckland should get more is exactly right and completely agrees with me - there is no point in spending $800m on this when you could just spend $50m and create a cycle lane out of the existing infrastructure. That's a ~$700m saving that can be spent elsewhere...

We should give the Billions to a Free Cycle E-Bike Company, run by Awkland Council and shift all those Commuters by e-bike from one side to the other and remove all those one seat filled Gas Guzzlers, thereby reducing traffic and leaving and entire land lanes to be re-utilised and removing the Combustion Engined Gasses and we will reduce Hospitals, via Keep-fit Exercises, when the Battery is turned off, if not in a hurry.

Plus we could buy all our Bike needs from China, thereby making China be-Holden to us as we could own the Company, a two way Win, in the Long-Run.

I would buy a Be-Holden E-Bike to get the Ball Rolling.....We could spread the idea arond the World....New Zeal-and-ers will never have to work again, if we can make it pay........Using Tax Payers Munny of course. Wheely sensible idea....

It's great how in the Netherlands they have magic fairy dust that means no one get degenerative diseases eh? That's why they get 33% active mode share. Wait, what are those other 66% of people doing?

I quite enjoyed biking to work in the Canterbury storms the other day. I have water proofs so most of me doesn't really get wet, but experiencing the wind and rain is quite exhilarating.

Haven't had to drive to work in Christchurch yet, have biked every day for 8 years.

Not everyone gets to work from home

Perhaps it won't be used by commuters on freezing cold rainy days, but for sure it will be wall to wall cyclists and walkers every sunny weekend, a bit like how it is around the waterfront.

Explain why Copenhagen has such a high cycling use then.

You know dam well that thats not going to happen just like the skypath. The only ones getting paid are consults to draw up pretty pictures and charge millions. For starters we need a whole NEW harbour bridge before the current one falls down. They have a life expectancy and everyone's just ignoring the engineers.

The now-scrapped Mill Road upgrade, for example, was priced at $1.85 billion last year, but is now expected to cost $3.5 billion...

Best we see the feso (the one pager) on this one.
Who is, or now was the QS?.

Don't blame the QS. Wouldn't surprise me if suppliers have low balled their indicative pricing in the early stages of the design process to entice the project along, in hopes that the principal will decide the project has progressed too far to give up on it and will just find/divert funds from elsewhere.

Breaking news, some saying its the land acquisition costs that have rocketed, the joke is on....

Note these projects would have opened up lower cost to build housing areas..

Evil genius or just plain stinky?

All sorts of fun and games I imagine.
There will be some consulting firms and contractors pissed off by these project cancellations.

So....... no port move North, no motorway, silence on the navy moving North, just a rail link into Marsden Point. Labour have sh*t canned all but one of the big 4 initiatives for growth in Northland. Bring back Winston? Or even Simon (one way) Bridges?

Rail to be port is a big improvement. Add in the Otiria inland port terminal and I can see lots of logging trucks off SH1 north of Whangarei.

And you are overlooking the benefits off safety improvements on SH1, which will improve traffic flow.

The RBNZ cut interest rates in half five times since July 2008. When interest rates are cut in half the present values of future cash flows are doubled for both assets and liabilities.

When the Fed engineered its experiment to promote the wealth effect, the family with savings experienced an increase in the present value of their assets and also an increase in the present value of their liabilities. Because our financial assets are traded in markets and because we receive mutual fund and retirement account statements, we promptly saw the change in the value of our assets. We are much slower to appreciate the change in the present value of our liabilities, particularly the value of our future consumption expenditures. Link


That's an absolute disgrace! Original cost estimate $6.8 billion 18 months ago, now $12.8 billion, That's $6'000 million more !!! That's 88% above budget and these costs will keep climbing. Yes Covid happened and it can explain some small lift in cost but not $6'000 million.
What a bunch of clowns, just imagine trusting them with costing and building a light rail system...

Hey Yvil you're channelling the FHB angst!

He's a DGM!!!

The people who got the prices wrong are not affiliated to any party, they are the engineers and consultants paid to do this work. The same thing happens when national are in power, it's an occupational hazard for all infrastructure projects.
Just another day in the office really.


We have great ideas, vote for us, we'll:
- build 100'000 affordable homes
- plant 1 billion trees
- reduce child poverty
- build heaps of roads
- and so much more, we're great, vote for us.

- Hey, we actually have no idea how to do these things or how much they cost, bummer… what are we going to do?
- Well borrow lots of money!
- Great idea !
- S#!t, it's still not enough
- Oh well, let's just NOT do this, people won't mind

Haha, classic. Good work

Hand out cash to beneficiaries instead and call it a moral budget

The walking bridge will cost $4.43 per return trip, if 10,000 return trips are made every day for the next 30 years and a final cost of $485m. Can you imagine sharing the cycle path with that many commuters? Will 10,000 commuters use the bridge every day? Build it and they will come!

This is nuts.

Let's pour billions down the drain on unnecessary 'green' transport projects while also paying the masses more in benefits to sit at home. Oh the irony at play here!

I got the numbers wrong. The cost is $685m and the expected trips are 1700 per day (1% of 2019 trips). That bumps it up to $25 per trip over *50* years

Its probably not as bad as it sounds. We don't seem to mind spending billions on expressways so around 10,000 people a day can get there a little bit faster. At least this offers a new mode of travel and a serious way of avoiding congestion, not just "a bit quicker road"
Judith Collins comment is so right wing isn't it. Just because you supposedly can't get your supermarket shopping on a bike that doesn't make bikes useless. You probably wouldn't go and get your shopping in a milk tanker either.

I can easily fit a week's shopping in my pannier bags, usually just using 1 and a reusable bag over my shoulder for bulky items. Could easily bring out my 3 pannier bags if I had to do a mammoth shop, or my bike trailer if I'm feeding the 5,000.

Great. Not all of us have the time to make all our trips by bike. That's a privilege that people seem all to keen to project over the whole population when it's a realistic option for a tiny portion of Aucklanders.

My friend just moved to Auckland and all I see from her is pictures of traffic jams she is stuck in. I wonder what proportion of journeys would be just as fast, if not faster, by bike? Especially with a e-bike.

It's the same in Christchurch - if you're going near the city centre a bike is just as fast and more convenient for parking.

Again - not for everyone, but we are way out of balance at the moment with everyone defaulting to cars without thinking of the alternatives. This is an enormous waste of resources.

Stuff did an article on this a while back. Pretty sure their results showed cycling was significantly faster.

I lived in blockhouse bay and commuted to the CBD every day and back for a year and a half. It's actually possible for a lot more Aucklanders than you think.

So your response to concerns about "projecting the privilege to actually be able to do something" is to project the fact you could do something across a huge number of Aucklanders because it worked for you personally?

The fact that you are confusing making a choice with privilege is odd to day the least. I spent less time on a bike than I would have in traffic. Nearly all those commuter trips into town each day are single people in cars. I am really not sure how my jumping on a bike is an example of "privilege".

Yeah look at those privileged cyclists - my commuter bike cost almost $500 10 years ago with ~$100 maintenance a year. The preserve of the wealthy for sure, normal people just knock out $5-10k on a car and a few k a year for fuel and maintenance.

How does riding a bike in flat chch compare to doing the same with the topography of auckland. It doesn't

No doubt somewhat easier. If you have a particularly hilly route an e-bike is a great option, much cheaper than a car and likely quicker in most cities. You can still get a little exercise and fresh air as you go, and easier to carry your shopping with you. In Chch we're blessed with calm weather and flat ground so regular bikes generally do just fine.

e-bikes - have you heard of these?

I'm not confusing choice with privilege. Your lifestyle allows you to make a choice to do something. Do you understand how this might not be possible or realistic for others?

One of the reasons it's not possible or realistic for others at the moment is the big wet gap in their potential cycle commutes.

Exactly what kind of lifestyle do you think I had? If you are talking about anyone dwelling in the old auckland city council bounds, there are certainly groups that couldn't cycle to work such as people with disabilities, people with jobs that require people to transport goods with them to and from work etc. But the majority of single persons in vehicles driving to and from work in the morning (in your words - a huge number of Aucklanders) are quite capable of being on bicycles or alternative forms of transport besides cars. Which would free up the transportation corridors for the people who really need them.

The cycle bridge across the harbour seems like overkill until you realise that the main bridge will hit capacity before the tunnel is built. #awesomeatinfrastructure

Northland being well rewarded for supporting Labour.

Kia Kaha Northland....... the important projects for Northland, not important to Labour.

I understand the government wants urban development from Hamilton to Whangarei, I presume the rail network will be running sub urban passenger services in the long run. The Marsden Point rail will serve an already sprawling collection of suburbs, Marsden, Ruakaka, Mangawhai etc.
It’s the suburban dream that becomes the suburban nightmare.
Hardly a reward.

Their vision is bollocks. It's all based on Twyford fantasies that haven't been killed

Northland needs investment in our communities, not in our roads. The provincial growth fund was dare I say it heading in a much more appropriate direction in this regard. I just wish we had a bit more time to come up with the meaningful proposals to get into that system (which has now had the guts ripped out of it). If we invested a small proportion of the funds about to be spent on Marsden to Whangarei in community projects the change would likely be transformational and would start a cascade of positive effects that Northland so desperately needs.

I wonder how many "shovel ready" projects out in the provinces are quietly being shelved?

Don't you mean 'buried'?

it was a typo .. they meant "shove ready".

"Shovel ready projects" is a laughable term. They simply don't and never have existed. Conjuring then up our of their backsides has been an extremely stressful exercise for all involved in the industry. Can we please never use this term again out if respect for the good workers it has broken.

Labour had their priorities right. The cycle tracks will help gentrify the existing neighborhoods- probably adding another 50 grand to every house near these amenities.

Be quick.

785 million would be a decent down payment on the tunnel. The extra capacity would allow conversion of a couple of the bridge lanes to cycle ways. Approve the disposal of the tunnel spoil along the foreshore and I'm sure the cost would come down significantly. Govt has authority to run rough shot over RMA, just needs the will to do it.

The sensible thing would be to build a whole new bridge or tunnel and just use the existing one for walking and cycling until it falls into the ocean. By the time they finish a new bridge the current one will have probably gone splash anyway. You can tell that nothings going to happen for 50 years. Seriously cars will be flying before it happens.

or run a free bus ,modified with bike racks,as a shuttle service for a year and use the numbers to assess the real demand.

The Harbour Bridge is rubbish as a cycleway or walkway. The gradient is not for newcomers. A tunnel is rampant overkill and will require extensive widening of the motorway to feed into it, because you'd still need the existing lanes to feed the bridge. And it would achieve very little that you couldn't get with a public transit (light rail) bridge anyway - which you could just stick some walking and cycling spaces around and call it a day.

An extra bridge with no rapid transit is bad but a tunnel is worse.

800 mill would build a tonne of housing

The government put $3.8 billion towards housing in the budget two weeks ago. We can walk and chew gum at the same time.

Simply looking at a map of Auckland tells you there is no way you can have reasonable cycling infrastructure without being able to cross the harbour, it's crazy this hasn't been done yet. Cars are necessary in some cases but whatever we can do to get people out of them when they don't need to be in them, the better.

The outcome was to be expected & self inflicted.

Labour Party
"We also won’t raise fuel taxes"

IMO Rampant house price inflation is causing knock on inflation in other areas, as it has allowed suppliers to increase their prices due to huge demand. Building has gotten more expensive because existing house prices have risen so much, so building has become a cheaper option in some cases. If the government isn't borrowing the printed money, then it is going to end up being lent to the banks and they will lend it on housing at even lower rates, and pushing up prices even more. These roads are cheaper to build today than they will be in the future.If they are bring in people to increase the population, then they are going to need to build the infrastructure. Increases in population has costs down the track.

What a load of ridiculous, climate change denying, last century comments from those National MPs.

I can't wrap my head around a doubling of project costs. Were the original costings woefully inaccurate? Or is there gouging going on because the government is shovelling out easy money?

Projects go through a number of stages. Each progressive stage collects more and more detailed information and develops the design option in such a way that costs and risks are better defined. There are general industry expectations that certain phases will have certain cost variants (30-50%, 10-15% etc) to the final out turn number, but the truth is each project is very different and some are just straight up unique, have very unusual risks that are realised, or just everything that could ever go wrong does.
Waka Kotahi have a good cost estimation procedure they make all consultants follow, it produces a 3 range estimate at each point including base - when nothing goes wrong, P95 - when more things go wrong than what you would commonly expect (but not everything), and P50 which is an educated opinion based on probability and practical experience on what may or may not go wrong that is often between 30-70% between the base and the P95.
Waka Kotahi fund / allocate the P50 estimate to the project, with the knowledge that there is a P95 that exists, but across their portfolio they are hoping the over and unders balance out, which is why if you exceed your allocation for a Waka Kotahi, there is usually an assumption that there is reasonable chance you can go back and get a bit more money if you end up going over. Do people generally underestimate the P50? Probably. Probably because sometimes if the P50 is too high they know their project might get shelved, and also because there is an inherent belief if things go wrong, and the project is already well underway / in construction, then you will get bailed out.
For this unique example? Many of the projects were in very early stages, so the estimates are inherently unreliable, as insufficient info at that stage.
But if you are asking for a project that is incredibly difficult to cost at any phase it is a second harbour crossing of any kind. Structures with materials very vulnerable to unit price fluctuations, the service relocation costs would be a nightmare to cost, as you can't until you are in detailed design and able to start negotiating contracts with service providers, so how long is a piece of string, consents and the resulting conditions, etc etc etc etc etc. Basically impossible to come up with anything sensible at an early stage, and that is unfortunately basically the truth.

Harbour Bridge Cycle way...I’ve got this !

For $685 M upfront I will provide cycle and walking access between Birkenhead point and Westhaven for the next 50 years. This will be running in 12 months.

2 x Shuttle ferries leaving every 20 mins in opposite directions
Electric ferries, roll on roll off with a fast dock landing either side.
Running 5:00 am to Midnight 7 days a week

Ferries $5 M the pair replaced every 10 years $50M
2 X Fast dock landing ramps $10M
Maintenance and operating costs $3M year $150M
Wages $250K Year x 50 years $12.5M to be replaced by robot auto ferries in year 10
Savings for Robot Ferries (paid as CEO Bonus Year 10 $5M)
CEO Compensation (me) $9M year x 50 $450M
Consultancy fee (me) $12.5M

Land for the docks - 50M+ purchase price and 15 years trying to get Council to release public land to a private business proposal.
Getting a plan change and consents to build the docks and associated access roading including stakeholder negotiations - 5M+ and a 10 year timeframe. And let's face it you'd never get them if it is not a venture being undertaken by a public authority.
Design of docks to comply with consent conditions which is works within the CMA - 3M+.
Redesign of all marine structures adjacent to your westhaven pier to take the additional loadings of your structure 25M
Procurement and Construction of your piers and associated roading 50M
Maintenance costs proportional to more realistic infrastructure investment costs - a lot more than what you said!
250k a year for wages depends if slavery is legalised in the next year. Skippers will need at least 70-80k each you're going to need 6-8 min of them to cover those hours and holiday pay. Then the jetty staff, ticket collectors, people taking phone orders, etc etc
Robot ferries do sound fun.
CEO compensation - well you'd never get off the ground so you wouldn't have to worry about this cost.
Consultants (not you) they'd make a killing and they'd be the only ones to benefit from the project in the end...

While you are driving along the road and breathing Benzo(a)pyrene, somewhere nearby in a beautiful park, I breathe pine air, exercising on the bike path.