NZTA Predict No Growth For Matakana

This is the third 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 bettertransport.org.nz

Previously I pointed out that the NZTA produced Traffic Assessment Report hasn’t factored in a toll for the Puhoi to North Warkworth Toll Road (PNWTR), thus overstating expected volumes on the proposed route. Before that I made the case that traffic growth assumptions for the corridor aren’t based on current trends, and that the forecast number of trips “further north” was overstated in the report to the Board of Inquiry.

In this post I examine NZTA’s forecast growth in traffic for the Matakana region and Warkworth.  Matakana Road is the route to the Omaha, Leigh, Goat Island and numerous other coastal destinations. These destinations are very popular during weekends and holiday periods.

Here’s the 2009 Base Case traffic counts taken from figure 11 of the report:

And here are the 2026 traffic volumes predicted by NZTA’s model:

As you can see, the model predicts Matakana traffic volumes to increase by only 500 for the Base Case in 2026, and by 700 for the Project Case.

In my view this is highly unlikely.  The model even predicts south bound traffic volumes to decrease by 20 trips a day for the “Holiday End” periods for the Base Case, and remain the same for the Project Case.  In my experience, the ends of long weekends and holidays are the busiest times on Matakana Road.  The implied growth of 0.3% per annum in AADT traffic volumes does not make sense, especially when you consider the number of new dwellings that will probably be built in the Matakana region in the next 17 years by 2026.   If this is the same assumption used to model the Hill Street intersection, then delays are likely going to be far greater in reality than forecast.

It is even more odd when you compare the Matakana Road growth assumption with that used for Sandspit Road, which connects to Snell’s beach and the Mahurangi peninsula.  Those figures work out to be a linear growth of 2.9% for the Base Case and 3.0% for the Project Case, which is more in line with what one would expect.

The land use assumptions are on pages 8,  13 and 14 of the report. For the Base Case and Project Case, this includes land-use changes (growth) in Warkworth.  For the Project Case, the following adjustment was made:

So even though it isn’t in the Warkworth Structure Plan (or the Unitary Plan?), the growth has been modelled to take place near the northern junction of the PNWTR. To the author’s credit there was a sensitivity test done on this assumption:

So 20% more traffic on the existing SH1 for the more likely growth scenario, than shown in the main body of the report!  So instead of 14,500 veh/day, traffic volumes on the existing SH1 are more likely 17,300. And presumably 2,800 veh/day less on the toll road.   No wonder it is buried at the end of the report.

My next post will cover one final traffic modelling issue, before moving on to the topics of economics, safety and consideration of alternative routes.

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