44 Bowen Street
Private Bag 6995
Wellington 6141
New Zealand
T 64 4 894 5400
F 64 4 894 6100
www.nzta.govt.nz
3 October 2025
AJ
[FYI request #32017 email]
REF: OIA- 19318
Dear AJ
Request made under the Official Information Act 1982
Thank you for your email
of 15 August 2025 requesting information under the Official Information Act
1982 (the Act). I have responded to each part of your query below.
This request covers information used to justify decisions not to upgrade the interchange to ful
access, including but not limited to:
To provide further context, NZ Transport Agency Waka Kotahi (NZTA) excluded a northbound on-
ramp/ full-access design at the Cambridge Southern Interchange during the design and planning of
the Waikato Expressway Cambridge section. The interchange at Tirau Road was specifical y designed
for southbound movements so that the expressway would not be used for short trips (for example on
at the Southern Interchange, off at SH1B interchange).
We determine our position using a whole‑of‑network approach to the Waikato Expressway. This
approach considers long‑term strategic planning as well as more specific transport planning
assessments related to projects or activity in the area, such as the recent resource consent for a new
quarry. We also consider ongoing traffic counts on the network, and planning and assessments
undertaken by Waipā District Council as part of their transport projects.
I have provided further detail on the sources consulted to determine our position in parts 4 and 5 of
your request.
1) When NZTA conducted its most recent traffic flow modelling relevant to the Cambridge
Southern Interchange.
In 2011, using the Waikato Regional Transport Model (WRTM), NZTA conducted model ing relevant to
the form and extent of the Cambridge Southern Interchange as part of the Waikato Expressway
Network Plan. The plan is available online at:
www.nzta.govt.nz/assets/Uploads/waikato-expressway-network-plan.pdf.
2) Where the traffic data used in that modelling was sourced from (including specific traffic counts,
third-party datasets, or local authority data).
3) Population growth models for Cambridge used in that model ing, including the source of those
projections and the version/date of the dataset.
NZTA has performed a thorough search of our records and has been unable to locate the specific
model ing data, outputs and inputs used in this model ing. WRTM applications prior to 2018 were held
across multiple systems, some of which are no longer accessible.
As such, I am refusing parts two and three of your request
under section 18(e) of the Act as the
document al eged to contain the information requested, despite reasonable efforts to locate it, cannot
be found.
WRTM forecasts traffic movements based on:
•
Input demographics – Current year information is sourced from the Census. Future
projections are sourced from Statistics NZ and a specific land use model of the Waikato
Region.
•
A simplified representation of the transport network: The future transport network is
developed based on committed or anticipated projects, which is specified by relevant local
authorities.
•
Mathematical parameters derived from observed data: The mathematical model
parameters are estimated from observed behavioural data, including Household Travel
Survey.
•
Traffic counts - Model outputs for a current year are compared against traffic counts to
quantify their representativeness. Traffic counts are provided by relevant local authorities.
More technical information on WRTM is available at:
www.colabsolutions.govt.nz/shared-services/wrtm/.
4) Any model ing assumptions, reports, and methodology notes relating to the Cambridge
Southern Interchange, including assessments comparing its location to the Victoria Road
interchange.
5) Any analysis or examples NZTA has considered when citing that the Cambridge Southern
Interchange is "too close" to Victoria Road interchange and would result in mainly local traffic as
reported https://www.cambridgenews.nz/2025/08/upston-ramps-up-support/. Including
comparisons to interchange spacing elsewhere in the Waikato Expressway or Hamilton area.
There are 8 documents that fall within scope of parts 4 and 5 of your request listed in the appended
document schedule and are enclosed.
Certain information has been withheld under section 9(2)(a) of the Act. This section al ows for the
withholding of information to protect the privacy of natural persons.
With respect to the information that has been withheld, I do not consider there are any other factors
which would render it desirable, in the public interest, to make the information available.
Whilst the Cambridge Southern Interchange was not included in the scope of the SH1 Cambridge to
Piarere project, there are documents within that project that included analysis of spacing of
interchanges on the Waikato Expressway and have helped us inform our position. Please refer to
attachment 7 for this information.
2
In attachment 8, we’ve included a screenshot from the NZTA open data map State Highway Traffic
Monitoring – Annual Average Daily Traffic which shows the Annual Average Daily Traffic (AADT) count
for site 1N20576 (the site closest to the Cambridge Southern Interchange). The current AADT for this
site is 9,054.
The corresponding graph for the past 5 years indicates that traffic growth has not reached the levels
anticipated at the time the interchange was designed and constructed. For example, Figure 5.2 of the
Waikato Expressway Cambridge Traffic Assessment in attachment 3 projected a daily traffic flow of
12,600 at this location. You can find the open data portal on our website here:
https://opendata-nzta.opendata.arcgis.com/.
6) Copies of any NZTA/Waka Kotahi policies, guidelines, or criteria relied upon when determining
whether to upgrade the Cambridge Southern Interchange to a full access interchange.
Guidelines to highway design standards are publicly available on our website:
www.nzta.govt.nz/roads-and-rail/highways-information-portal.
NZTA is developing a Strategic Transport Plan for the Hamilton to Tauranga corridor in the near
future. This plan wil assess long‑term changes across road and rail networks and identify potential
improvements over the next 30 years.
NZTA is also working with Future Proof partners, including Waipā District Council, on a spatial study
for the corridor. This study wil provide high‑level analysis of growth opportunities, focusing on
economic development, land use, and planned Roads of National Significance transport
improvements.
Under section 28 of the Act, you have the right to ask the Ombudsman to review my decision to
withhold information or refuse part of this request. The contact details for the Ombudsman can be
located at www.ombudsman.parliament.nz.
If you would like to discuss this reply with NZTA, please contact Ministerial Services by email to
[NZTA request email].
Yours sincerely
Prisca Gain
Team Leader, Ministerial Services
3
OIA-19318 Document Schedule
Ref
Document
Date
Comments
1.
Waikato Expressway – Cambridge section
July 2010
Released in full
Options assessment summary document
2.
Waikato Expressway – Cambridge section
December 2010
Some information
assessment of environmental effects
withheld under
section 9(2)(a).
3.
Waikato Expressway: Cambridge section
6 December 2010
Some information
traffic assessment
withheld under
section 9(2)(a).
4.
Waikato Expressway, Tamahere Cambridge November 2012
Some information
Section Traffic model ing report
withheld under
section 9(2)(a).
5.
Former SH1 and SH1B Routes Tamahere to November 2015
Some information
Cambridge form and function statement
withheld under
section 9(2)(a).
6.
Cambridge Section traffic effects on local
Unknown
Released in full.
road network
7.
Excerpt of detailed business case network
July 2017
Some information
connection summary report SH1 Cambridge
withheld under
to Piarere
section 9(2)(a).
Some information
marked out of
scope.
8.
Traffic data
September 2025
Released in full.
4
