Alcohol and other drug use in New Zealand drivers, 2004‐2009,
Dr Helen Poulsen of Environmental Science and Research Ltd (ESR) has completed a report into alcohol and other drug use in New Zealand drivers.
Background
This report was prepared by Dr Helen Poulsen of ESR, using funding secured by the New Zealand Police under the Cross Departmental Research Project Grant. The purpose of this study was to investigate the prevalence of alcohol and drug use by drivers on New Zealand (NZ) roads.
Methodology
This study examined two different driver samples. The first sample involved drivers killed as a result of a crash during the period 1 July 2004 to 30 June 2009. This sample consisted of 1,046 deceased drivers. The second sample consisted of 1,999 evidential blood samples taken from suspected intoxicated drivers not involved in crashes, which were collected over a six month period. All samples were screened for the presence of both alcohol and drugs.
Findings ‐ Deceased drivers
Of the 1,046 deceased drivers tested for the presence of both alcohol and drugs:
- 546 (52%) of drivers were not impaired by alcohol or other drugs.
- 500 (48%) of drivers tested positive for the presence of alcohol and/or drugs.
Of these 500 drivers who tested positive:
- 135 (27%) recorded the presence of alcohol only;
- 96 (19%) recorded the presence of cannabis only;
- 142 (28%) recorded the presence of both alcohol and cannabis (but no other drug), and;
- 127 (25%) recorded a combination of drugs, including the combination of alcohol and/or cannabis.
Of the 127 deceased drivers who recorded a combination of drugs (other than alcohol or cannabis):
- 23% recorded the presence of opioids (such as codeine or morphine);
- 31% recorded the presence of sedatives (such as diazepam), and;
- 42% recorded the presence of stimulants (such as methamphetamine).
Findings ‐ Drug use in suspected drunk drivers
Of the 1,999 evidential blood samples further tested for the presence of drugs (other than alcohol):
- 1,258 (63%) recorded the presence of alcohol only;
- 695 (35%) recorded the presence of both alcohol and cannabis, and;
- 46 (2%) recorded the presence of alcohol and some drug (other than cannabis).
Limitations
There are a number of limitations with this study that must be considered alongside the findings of this report. Overall, it is important to note that this study uses both limited and biased samples. Consequently, the results of this study can only be considered indicators of possible drug use in the wider driver population. Therefore, drawing generalisations about the wider driver population need to be treated with caution.
Furthermore, it is important to acknowledge that the presence of drugs and alcohol in the study samples does not necessarily infer significant impairment. For instance, within this study, a deceased driver was considered impaired at the level of 30mg/100ml of blood (or greater). For drivers of the age of 20, this level falls well below the current legal limit.
In terms of the presence of other drugs, there are two main limitations. Firstly, due to a lack of a strong correlation between tetrahydrocannabinol (THC) levels and driver impairment, the presence of THC in the blood samples does not necessarily infer impairment. Additionally, in the evidential blood driver sample, the methodology used to determine the presence of a drug does not constitute proof of drug use, nor does it infer driver impairment. Further analysis of these samples to confirm the presence of drugs was not conducted.
For further information
If you wish to receive a full copy of this report, please contact Road Policing Support in the first instance.
Or you can download a full printable copy of the report Alcohol and other drug use in New Zealand drivers, 2004‐2009 Report [PDF 771KB] from our website.
