Adding up the benefits of the Christchurch Northern Corridor

Analysis: It’s fair to say that the Christchurch Northern Corridor (CNC) is a contentious project. There are significant costs involved (both financial – more on that in a future article – and in terms of community impact, especially on those living downstream). Given these costs, surely there must be significant benefits on the other side of the ledger?

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CNC benefits from the project website

In a previous career in the technology sector, I’ve been involved in big-ticket product development decisions. These might have been an order of magnitude smaller than a Road of National Significance, but they still required a comprehensive business case.

I’ve been prompted by the current Council consultation on the downstream effects of the CNC to look beyond the headline claims for the project (‘reduced travel time’, ‘improved safety’ etc). Where is the business case for the project, what does it say, and how do the benefits stack up?

The claimed benefits for the CNC can be found on the project’s website. After unsuccessfully searching online for details behind these claims, I submitted a request to the NZ Transport Agency. I asked for a copy of the Business Case or similar document that captures the overall costs/benefits etc of the project.

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Released under the OIA: the Final Scheme Assessment Report

I was eventually provided with a 2011 ‘Final Scheme Assessment Report’, which I understand to be the document that went to the NZTA Board at the time that the project was approved. (NZTA have noted that the project as it’s now being built includes components that weren’t in that report, such as a full-length shared use cycle/walking path, and a 3rd southbound lane over the Waimakariri River, however the project was approved without these, so this analysis excludes them.)

From the NZTA report, I’ve quantified the project’s benefits as best as I can:

CNC Benefit (from project website) Further detail*
“Improved travel times – shorten travel times in and out of Christchurch and improve reliability via all main routes.” 8 minutes per vehicle saved during peak periods for the journey between the Waimakariri River and CBD.

Trip reliability benefits were not modelled & were excluded from the business case

“Improved access – All modes including freight will move more efficiently in and out of Christchurch and Lyttelton Port.” Improved access is described as a ‘key strategic driver’ for the project, but doesn’t appear to be quantified.
“Safer streets – moving heavy traffic off suburban roads making them safer and encouraging walking, cycling and the use of public transport. The new motorway will be built to high modern safety standards.” One fatal/ serious crash (or casualty) saved per year on average.

(More recent information on safety: this 2019 video on the central median barrier on QEII Drive and Cranford St.)

“Improved options for all modes – As well as the motorway, there will be an off-road cyclist/pedestrian route that includes safe access over the Waimakariri River. Space for an improved public transport corridor on Main North Road/Papanui Road and options for express routes, high occupancy vehicle lanes, park and ride and other facilities.” 300 new cyclists / 600 new pedestrians a day [based on the 2011 plan to have 5km of cycle/walking path]

Refers to “aspirations for improved Public Transport … on the Main North Road corridor”. Traffic on Main North Road is forecast to reduce by approximately 40%.

“Economic growth – enable sustainable residential development in the north of Christchurch and support commercial and industrial development throughout Canterbury.” Having read the report I’m still unclear how the CNC enables ‘sustainable residential development in the north of Christchurch’.

From the report: “Improved travel time reliability will contribute to the economic development of Christchurch and Canterbury.” – this doesn’t appear to be quantified.

“Reduced congestion” Reductions in travel times and in traffic on Main North Road are mentioned above. (But on the other hand, Cranford Street traffic is forecast to increase by 76%. The report gives no consideration to downstream impacts.)

Congestion relief may improve air quality overall (details are in an appendix that I haven’t seen).

(This 2019 video mentions ‘reduced congestion’ in the context of 4-laning QEII Drive and Cranford St.)

*The ‘further detail’ in the table is derived from the 2011 Final Scheme Assessment Report unless otherwise noted.

Question for readers

Is there anything here that surprises you? Are these benefits adequate?

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