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4 March 2026
Hayden
[FYI request #33252 email]
REF: OIA-21001
Dear Hayden
Request made under the Official Information Act 1982
Thank you for your email of 4 February 2026 requesting the fol owing information under the Official
Information Act 1982 (the Act). I wil address each part in turn.
1. Methodology Documentation
Please provide the methodology document(s) explaining:
(a) How CAS determines whether drugs "contributed" to a crash versus were merely "present" in a
driver's system
(b) What toxicological thresholds or criteria distinguish "presence" from "impairment" from
"causation"
(c) Whether "contribution" is determined by attending officers, crash investigators, toxicologists, or
some combination
NZ Transport Agency Waka Kotahi (NZTA) does not hold methodology documents determining
whether drugs caused or contributed to a crash.
CAS is a descriptive crash database. It records whether drugs were suspected or present in road
users involved in crashes, but it does not distinguish between presence, impairment, or causation, and
it does not determine whether drugs caused a crash.
Police Traffic Crash Reports record whether alcohol or drugs were present (for example, positive or
negative test results and broad drug categories). Police do not record or determine drug causation
within the Traffic Crash Report. CAS factor coding and summarisation is undertaken by NZTA using
information supplied by Police, but CAS does not apply toxicological thresholds or determine scientific
causation.
Accordingly, the methodology documents you have requested is being refused under section 18(g) of
the Act as the information requested is not held by NZTA and there is no reason to believe it is either
held by, or more closely connected to the functions of another government agency.
Please find enclosed
OIA-21001 CAS data.xlsx, which provides contextual information about how
drug-related factors are recorded and summarised in CAS and should be read in conjunction with the
explanatory notes included in the spreadsheet.
2. Data Reconciliation
The Factors sheet shows "Drugs proven" = 337 crashes and "Drugs suspected" = 11 crashes
(total 348), yet Data1 shows 528 crashes where "drivers with drugs contributed to a crash."
Please explain this 180-crash discrepancy and provide reconciled figures.
The enclosed spreadsheet includes:
• the relevant factor counts for fatal crashes between 2019 and 2023; and
• an explanation of the difference between the “drugs proven or suspected” figure and the count
of crashes where drivers had drugs recorded as contributing.
The notes explain how crashes involving both alcohol and drugs are counted, how non‑drivers are
included in some factor summaries, and why figures drawn from different CAS outputs are not directly
comparable without reference to these counting rules.
3. "Other Drugs" Breakdown
Please provide a breakdown of the 141 "other drugs" fatal crashes by drug type, specifically
distinguishing between:
•
Methamphetamine
•
Prescription medications (sedatives, opioids, benzodiazepines)
•
MDMA/party drugs
•
Other il icit substances
The data supplied provides the requested breakdown of fatal crashes involving drugs other than THC,
including methamphetamine, prescription medications, MDMA/party drugs, and other il icit substances.
The accompanying notes explain how crashes involving more than one drug type are counted and
why totals may not sum cleanly across categories.
4. THC-Specific Causation Analysis
For the 118 crashes where "THC alone" was recorded:
•
THC blood concentrations
•
Explanation of how contribution was determined (vs prior, non impairing use)
•
Whether other factors (speed, fatigue, weather, etc.) were also present
The spreadsheet includes a table showing other contributing factors recorded in fatal crashes where
THC was the only drug coded as contributing for the driver(s). This provides contextual information
about other crash factors recorded alongside THC‑only.
NZTA does not hold information on THC blood concentrations or analysis determining whether THC
caused these crashes as opposed to being present from prior, non‑impairing use. This part of your
request is therefore refused under section 18(g) of the Official Information Act, as the information
requested is not held by NZTA.
5. Policy Basis Question
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Given that your own data shows THC alone contributes to approximately 8% of fatal crashes (not
30%), please provide any analysis, briefings, or advice provided to Ministers or decision-makers
that:
•
Separates THC-specific risk from general “drugs”
•
Evaluates whether oral fluid testing is evidence-based given THC accounts for ~8%, not
30%
This part of your request is more closely connected with the functions of Ministry of Transport (MoT)
than with NZTA. Therefore, this part of your request was transferred to MoT under section 14 of the
Act.
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.
Under section 28 of the Act, you have the right to ask the Ombudsman to review my decision to refuse
this request. The contact details for the Ombudsman can be located at
www.ombudsman.parliament.nz.
In line with NZTA policy, this response wil soon be published on our website, with personal
information removed.
If you would like to discuss this reply with NZTA please contact Ministerial Services by email to
[NZTA request email].
Yours sincerely
Josh Driscol
Manager Ministerial Services
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