Monday, August 27, 2012

Drugged Driving Nerd; Beyond the Press Release

Good on the NZ Herald's Nicholas Jones copying and pasting a PR and picking up the phone a couple of times, but the ESR report on drugged driving in NZ he glosses over is far more interesting than the sound bites imply.

So why trust me on the subject? Well, apart from having some experience in drug driving from all sorts of angles, I helped put together NORML New Zealand's select committee submission on drugged driving some years ago. Short story, we cautiously favoured a 10ng/mL limit, while acknowledging the wildly subjective nature of doing so. You can view it here. I have also read P.J. O'Rourke's classic How to Drive Fast on Drugs While Having Your Wing Wang Squeezed and Not Spill Your Drink.

The Herald's headline is wrong. The study did not find the most crash drivers had taken drugs. 546 of the 1046 drivers (52 percent) whose blood was analysed were found to be unimpaired by drugs or alcohol.

All sorts of other true yet sensational headlines were possible for the NZ Herald, given the contents of the report (it's here, not that the Herald wants to disclose its publicly available sources or anything); "Females appear more likely to drive on sedatives, as opposed to alcohol or cannabis" would be one. "Maori over-represented in alcohol and cannabis driver deaths" might be another. "Straight people five times more likely to kill than cannabis only drivers" is getting warmer, but "Everyone's on drugs in Auckland, yet few people die on the roads there" would probably be the angle I'd go with.

The study in question polled two groups. The main group of 1046 dead drivers, a census of NZ road deaths spanning a five year period between 1st July 2004 and 30th September 2009, was by far the most interesting. In pleb-speak, the ESR could go all CSI on these dead drivers' blood samples.

The basic PR is mainly true:
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).
But the detail is so much more fun. Let's see now... 42 percent of 127 is 53.3. Over those five years, ten people a year died with stims in their blood. That's far less of a bad stat than drownings or suicide, for sure.

No, when you're talking about drugged driving, they're talking about cannabis. If they were thinking of alcohol, they'd say drink driving. And that universal problem solvent of alcohol is still most of the problem. Even Auckland MASH wonk Dr Tim Parke couldn't ignore that pink elephant in the waiting room on Nine to Noon today.

The report has this to say about driving under the influence of cannabis (page 18):
There is not a strong correlation between THC blood levels and impairment.

The report goes on to note that single vehicles accidents are more common in alcohol and alcohol with cannabis deaths (tree, power pole), however cannabis only deaths occurred more frequently in multiple vehicle crashes (trucks, and lots of motorbikes hitting cars).

The report looks at odds ratios, drilling right down to how the 18 (of 96, out of 1046) non-culpable cannabis only drivers and how they died. The comfortably numb motorcyclist (18ng/mL) getting killed by a car who failed to give way was sobering enough, but this poor bastard wins the Milan Kundera Award for this ending:
Car hit another then crossed centre line into path of van driven by deceased
Dodge that one, possum.

I do not support Farrar or AA's call for random drug driving testing. Alcohol is still by far the biggest problem. What I would really appreciate is a mature an honest approach to driving and to drugs. To coin Hunter S. Thompson, you can turn your back on a person, back never turn your back on a drug, especially when that drug is steering a ute home from the pub.

And if that doesn't sway you, consider this. The twisted nature of the polydrug damage this report sought to consider, can easily be replicated within the alcohol only group alone. Anyone who has ever mixed their grains and grapes will agree.

Thanks for reading. You've earned a bit of Suzanne Vega: