This is the fourth 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 for the Puhoi to North Warkworth Toll Road (PNWTR) is not realistic in a number of areas:
- Traffic growth assumptions for the corridor aren’t based on current trends
- Growth assumptions for Warkworth aren’t based on the Warkworth Structure Plan
- The forecast number of trips “further north” is overstated
- No growth has been assumed for Matakana
- No toll tariff assumed for the new $760m toll road
It is very hard to appreciate the significant combined effect of these erroneous assumptions, so I’ve modelled the outcome in this table:
The more realistic input assumptions mean the result is 56% less traffic on the toll road, and 50% more on the existing SH1 than NZTA’s forecast.
This is significant, not just because 6,031 really is a pitiful amount of traffic for a $760m toll road, but because one of the objectives of the toll road is to reduce congestion at Warkworth. Current AADT volumes are about 17,400 veh/day, so traffic volumes of 21,788 represent an increase in traffic volumes of 25% by 2026 on the existing SH1. Without improvements to Hill St, delays will get far worse after the project is completed. It also means the claimed safety benefits are doubtful. There aren’t any safety improvements proposed for the existing SH1, so the number of accidents will be higher than NZTA’s report also. I’ll be talking more about this in a subsequent post.
The assumptions that I have used are laid out here:
Stepping through each assumption:
- Project scenario straight line growth. Although the NZTA’s own Economic Evaluation Manual stipulates a zero default growth rate should be used, I have based growth on the historic trend of 2.1%. Incidentally if you use a higher growth rate than this, more traffic results on SH1.
- Toll route % traffic: This is the split of traffic assumed without a toll. I’ve simply used the same split identified in the original report.
- Warkworth Plan Increase in SH1: The 2,800 increase in traffic on SH1 comes from Test B of the original report. I’m assuming this because most new growth is currently planned to be in the west and south of Warkworth. Obviously if there is an increase in traffic on SH1, there must also be a reduction in traffic from the toll road.
- Matakana straight line growth: The original report assumed virtually nil growth, but here I’ve assumed the same growth for Matakana Road as for Sandspit Rd. I’ve assumed 50% of the additional Matakana traffic will take the toll road. The 50/50 split is roughly the split the original report claimed. Although NZTA have since retracted this split, I’ll run with this for now.
- Toll diversion: The effect of any toll is to divert traffic on to the free alternative. I haven’t modelled a toll tariff amount, I’ve simply assumed that the NZTA will set a toll that will divert about 15% of the “further north” traffic and 80% of traffic to Warkworth and the eastern beaches. There is a greater diversion of traffic for these destinations as the existing SH1 is already forecast to be quicker. I’m just assuming 20% of these trips will be on the toll road because of the increased safety and comfort of the toll road, even though the trip will take longer. (Off memory, about 25% of trips on the Northern Gateway corridor takes the free the Hibiscus Coast route.)
So there you have it. You can test your own assumptions by downloading the spreadsheet.