Two hours across Cook Strait
- Info
- Sep 24
- 3 min read
A new independent analysis that quantifies the benefits of Transmission Gully and Kapiti Expressways has been released. Infometrics prepared the report for Infrastructure New Zealand, Porirua City Council, Kāpiti Coast District Council and Wellington City Council.
The report shows Transmission Gully is a worthwhile infrastructure project with significant economic and social benefits. The report is timely and allows for a direct comparison of a recently delivered transport infrastructure project with that proposed by NSX, the consortium proposing a new ferry terminal and port for the South Island at Clifford Bay.
A basic comparison shows that NSX delivers 58% more total time saved every year and saves 3.2 more lives every year. NSX’s capital cost is 68% lower in real terms compared to Transmission Gully and NSX capital will be privately sourced. Private financing will relieve the taxpayers and Marlborough ratepayers of the Picton rebuild costs which are of a similar amount as that planned at Clifford Bay. And a rebuilt Picton does not deliver the economic and social benefits of time saved and lives saved that NSX will.
NSX also dramatically reduces and eliminates other anticipated costs of capital projects required from Marfells Beach Road on SH1 to Picton.
The table below shows a comparison of the headline numbers with comments.
Metric | Transmission Gully | NSX - Clifford Bay | Comments |
|---|---|---|---|
Average Trip Time saved | 9 minutes [1] | 150 minutes | 16.6x greater saving per trip |
Total Time saved Annually | 1.9M hours | 3.0M hours | 58% more time saved per year |
Annual road deaths (lives saved) | 0 deaths saved per year | 3.2 deaths saved per year | Based on available CAS data between the period 2019-2025. Most deaths caused by fatigued drivers in the last hour of long journey as found by coroner report. [2], [3], [4] |
Annual serious injuries avoided | 0.2 serious accidents avoided | 4.4 serious accidents avoided | as above |
Capital Cost | $1,250M NZD of Crown capital [5] | ~ $900M NZD of private capital [6] | 68% lower capital costs when Transmission is inflated to $2025 (factor 1.21) |
Bypass investments | Pukerua Bay to Plimmerton upgrade Pukerua Bay to Paekakariki safety upgrade stage 1 Plimmerton to Paremata upgrade Pukerua Bay to Paekakariki safety upgrade stage 2 Plimmerton to Paremata clearway | Rail track maintenance between Spring Creek and Picton reduced SH1 maintenance and upgrades between Marfells Beach Road and Picton reduced Picton’s Dublin Street overbridge not required Blenheim bypass not required |
The average trip time saved for NSX is 16.6 times greater for NSX than for Transmission Gully, providing major benefits to passengers and freight users. The total trip time saved is 58% greater.
The annual number of deaths saved in Clifford Bay is 3.2 deaths per annum whereas the deaths saved by Transmission Gully in 2024 is nil. NSX also avoids 4.4 serious accidents per year. The combined economic and social benefits of avoided deaths and serious accidents using the same methodology used by Infometrics is $42M per year each and every year.
The capital cost of Transmission Gully is $1.25B NZD in 2022 dollars excluding completion, remediation costs and any liquidated damages arising from litigation. The capital cost of Clifford Bay is substantially less.
Transmission Gully allowed the Crown to avoid investments worth $51.3M in upgrades to the old coastal roading system.
NSX will allow the Crown to avoid and or reduce investments required totalling several hundred million dollars including: rail track upgrades, rail track maintenance between Spring Creek and Picton, SH1 maintenance and upgrades between Blenheim and Picton, the Picton Dublin Street overbridge and the Blenheim bypass. These avoided cost savings would fall on KiwiRail, NZTA, the Marlborough District Council and the Port of Marlborough. They are currently uncosted but in total are expected to be more than $100M.
In comparison a ferry terminal and port at Clifford Bay would bring our two major island closer together and return significantly better social and economic returns for much less capital.
References
[5] Excluding completions, remediation costs and liquidated damages resulting from a confidential settlement
[6] All estimated costs including connecting infrastructure and full rail enablement
