This is the second in a series of posts based on the Campaign for Better Transport’s submission to the Puhoi to Warkworth Board of Inquiry. The full presentation is over at

Yesterday I talked about the growth assumptions that lie behind NZTA’s traffic forecast for the Puhoi to North Warkworth Toll Road. (Because I think this a more accurate name for the project, I’m going to refer to it as the PNWTR).

In this post we are going to examine how NZTA have modelled the effect of the toll on projected traffic. The following chart is taken from the NZTA Traffic Assessment Report and shows predicted Annual Average Daily Traffic (AADT) volumes in both directions.

2026 volumes

The two columns on the left indicate the expected change in traffic between 2009 and 2026 if the Base Case (“do nothing”) option is chosen. These are the same figures as the chart that appeared on yesterday’s post.

The three columns on the right are the predicted 2026 traffic volumes should the PNWTR proceed.

The 2026 PNWTR Corridor Total figure is higher than the 2026 Base Case figure because the authors of the report “assumed that the operation of the Project will increase growth rates in the study area [and therefore] we assumed that an extra 1% of traffic growth in the Project scenario is a reasonable approximation of the induced traffic effects of the Project” (p.13). In other words the 2026 PNWTR model has an underlying growth rate of 5.4%.

You can see from the chart that NZTA expect 13,700 veh/day on the PNWTR route, and volumes on the existing SH1 to be roughly the same as what they are today should the project proceed. ( As noted yesterday, I have yet to reconcile how the figure of 13,700 veh/day on the PNWTR with the 5,930 veh/day for trips “further north”.)

Obviously though the split of traffic will be dependent on the toll. The report doesn’t explicitly say what the assumption is on the toll tariff, but buried on p.59 is this:


Translated, (and later explicity clarified with NZTA) this means that travel on the PNWTR extension of the existing toll road is assumed to be free.

In reality, however, NZTA acknowledge that:

  •  The PNWTR road will be classified as a toll road
  •  No decision on the quantum of the toll has been made
  •  If a toll was applied to the Project, depending on the level of that toll there would likely be a reduction in traffic on the new project route and a corresponding increase in traffic on the existing state highway

It would be extraordinary to classify the road as a toll road and then not charge a toll for its use. It would seem prudent to do some scenario analysis to find out what the impacts on traffic volumes would be. The risk is that the PNWTR ends up being like one of Portugal’s Ghost Roads, while traffic volumes on the existing SH1 will be far greater than the NZTA modelling suggests.

As I said to the BOI:

The importance of a realistic forecast cannot be overstated. The proposed toll road will most likely be with us for hundreds of years, along with the significant environmental impacts that come with its construction and operation. A realistic forecast that has considered all relevant scenarios is vital, and it is worth spending some time and effort making sure we get it right.

I’ve run out of time, so I’ll cover off the forecast traffic volumes for Matakana in a future post, along with other shortcomings with NZTA’s forecasting, before moving on to the issues of economics, saftey and consideration of alternatives.

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  1. Simply shocked that NZTA think they can model a project without a toll even though they’re planning to toll it.

    One assumes that once the toll is applied the modelling shows hardly anyone uses the new road and that’s highly embarrassing so they’re hiding it.

  2. Of course NZTA are well aware that their industry has a shocking record of significantly overestimating likely traffic volumes on toll roads:

    Recent experience in Australia:

    “Patronage of the tunnel decreased by more than 65% in the week following the introduction of a reduced toll period, and remains considerably lower than the predicted traffic.”

    …and that this can have very serious consequences:–revenue-forecaster-over-failed-toll-tunnel-in-brisbane-australia

    In NZ unfortunately it is the taxpayer that will be carrying the can for the resultant white elephant.—horrible-traffic-forecasts

  3. One thing that keeps bugging me Cam – why are the CBT against this designation? Whether the full project is justified now or not for 10, even 20 years is irrelevant, as one day a high quality solution will be justified. You said it yourself, that this corridor will last hundreds of years, when their will be no question of the roads importance, just like the motorway from Albany to Silverdale today. I think you’ll agree that part of the corridor should be used ASAP for a Warkworth bypass. So what are you aiming for, the NZTA being forced not to build the road? That would make building a Warkworth bypass much harder, and the NZTA would simply have to spend more money to do this all again sometime. I don’t see why a few dodgy traffic forecasts should be used to stop a road through a process concerning the environment, when the environmental impacts are so small. I’d appreciate if you could explain you’re reasoning for not wanting this corridor designated. To make a comparison, the ASL (Avondale – Southdown Line) corridor has been sitting around for years and years, and no-one seems to mind that actually building the line hasn’t happened yet due to economic justification.

    1. Hi Hamish, I will talk more on alternatives in a subsequent post, but obviously if the designation is approved then NZTA will build on it. Our preferred option would be NZTA build a bypass around Warkworth a la Mangatawhiri, possibly in the same alignment as the PNWTR, along with other changes. This will save $500m and forgo significant destruction of the environment between Puhoi and S Warkworth.

      1. I understand that you don’t want the project built soon, but why are you trying to stop it being designated now so it can easily be built in the future when it is justified? Shouldn’t you be trying to get the NZTA to look at your alternatives for the medium term instead of trying to stop them protecting the route for the long term solution?

        1. Hamish, as soon as the designation is given, the full $760m over scaled, environmentally destructive solution will be built. It would be naive to think otherwise. The Government wants it to proceed with the greatest possible urgency. Our option will never be considered if we agree to the designation. Capacity of 4 x 1,800 = 7,200 veh per *hour* which the PNWTR gives is not required, either now or in the foreseeable future. Our core argument is that the capacity will not be justified for the foreseeable future. If you are going to argue that it is required, then you need to argue why it isn’t required for the section from Warkworth to Wellsford. This will remain as a single lane each way for the foreseeable future.

          1. There is a huge opportunity cost in the haste to build this road. It overbuilds on a route that doesn’t demand it, it fails to meet the two immediate needs- urgent problems at Warkworth and a lethal existing road. In fact it strands the existing killer road as it is with no future ability to attract necessary funding. It talk capital away from other more vital projects. Particularly other road improvements as does the whole RoNS programme.

            We do contrast this with the reverse approach to the CRL but that isn’t the only issue here by any means. This is a crooked and rushed process by an agency not acting objectively but being forced into trying to justify on a project that can’t technically so it is doing dodgy stuff; omissions and exaggerations. We will end up picking up the ticket not only financially and environmentally but also because of the lost opportunity to invest in actually productive and necessary projects.

          2. Cameron, there are NZTA and LA designations all over NZ that haven’t been followed through to construction. The designation a useful legislative tool proved being very useful to earmark land for future development without the property, time and costs issues associated with trying to resolve at the time of construction. Designations also allow the planning stage to be extended to assist in determining the appropriate option and can also be given up if needed. Calling it naïve to think otherwise is not very defendable and appears that a bit of objectivity might be being lost as well as an attack on NZTA that isn’t justified.

          3. @lesley – that isn’t really relevant in this case as NZTA has signaled they they want to begin construction by late 2014, this isn’t a traditional route protection designation e.g. Avondale to Southdown rail line. Further, the BOI process is not just dealing with the designation, they are also responsible for determining the resource consents applications associated with the construction and operation of the road (e.g. earthworks, stormwater discharge). As consents such as earthworks have a typical expiry date of 5 years it is safe to say they want to get on with bulding it asap.

    2. I agree with Hamish here. We should be campaigning to get this project off the list, ‘Road of National Significance’, but allowing it to be a designated route.

  4. It depends on the price of the toll. Currently the vast majority of traffic uses the toll road. The cost of using the toll roughly equates to the cost in extra fuel, car wear etc of using the old road with the added bonus of saving 10 to 15 minutes. This will probably be the case with the new toll road. The cost being less than a flat white. I think a better argument would be if modeling demonstrated that modification of the existing road would cope with projected traffic increase yet cost less and be completed sooner.

    1. Hi Dennis, NZTA predict travel time savings for trips further north to be about 4 minutes faster than today using the PNWTR. So yes 5,930 veh/day will probably use the toll road at least. For trips to Warkworth, Matakana and the eastern beaches, the toll road will not be faster, according to NZTA modelling. The existing SH1 will be, so apart from safety, there is little incentive to pay the toll. I will address the safety issue in a subsequent post.

    2. The current toll road os a 15-20 minute saving on the free option this route will be comparable at best forthe majority of trips in this area.

  5. Straightening up and rerouting some of Dome Valley, a Wellsford bypass and some realignment work / bridges etc, at the Brenderwyns would offer much more benefit for the total journey at a fraction of the price.

  6. It would be worthwhile asking NZTA what measures they have taken to reduce optimism bias in their assessments. Here is a study commissioned by the Australian Department of Infrastructure and Transport after a series of financially disastrous toll road investments, and lists 21 areas where bias creeps in. Do NZTA have any revenue forecasts, which could expose taxpayers to obvious financial risk ?

      1. Let’s not get hung up with the semantics; optimism bias is just a natural tendency to select evidence in support of ones project rather than against it. It’s a real danger in technical projects and one method to counter it is to bring in an external auditor/ consultant to review the data and report to the board. I have been on both sides of fence.

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