Driving while....

The New Zealand Herald asked me for comment on a new study showing that driving while hung over is a bit riskier than driving while at the .05 level. I told them:

“It isn’t particularly surprising that driving while hung over increases accident risk. I would expect that driving while suffering from a very bad cold and headache, or driving with the flu, or being pretty tired, would have similar effect. In all of these we have to remember that increases in relative risk can be much larger than the actual risk imposed: if I’m thousands of times more likely to be killed by an asteroid when standing outside than while hiding in a bomb shelter, I’m still not very likely to be killed by an asteroid.”

“The reported risk increase here is more substantial than driving at .05. Drivers in the .05 to .08 range are about five times more likely to have an accident than someone who is sober, which is just a bit riskier than driving while having a conversation on a hands-free cellphone. I expect all of these are slightly less risky than driving with my five and three year olds in the back seat when they have conflicting views about what should be on the radio.”

A few "driving while" risks:

• Driving while using a cell phone, whether hands-free or not, is about four times riskier than baseline.
• Driving while using a cell phone, in simulator, is about as risky as driving while at .08, whether hands-free or not.
• But note that a really rather nice regression discontinuity design shows no real effect, and a potential upper-bound risk estimate around 3 times baseline. Ungated discussion here.
• If you're getting six hours of sleep per night, you're driving at the equivalent of .05. If you've been awake for 24 hours, you're comparable to someone at .10.
• Should we ban new parents from driving on basis of likely sleep deprivation?
• Older adults with cataracts (but still allowed to drive) were 2.5 times as likely to have had a history of at-fault crashes than those without cataracts. 
• Old people and young people are risky. Compared to 30-59 year olds (baseline), those over 70 have twice the risk of fatal accident involvement, as do 19 year olds. A 16 year old with passengers is 4.72 times as risky as a 30-59 year old with passengers; a 20-24 year old with passengers is 2.54 times as risky.
• Drivers over the age of 85 had 10.62 times the baseline risk of multiple-vehicle accidents at intersections and 3.74 times baseline risk elsewhere. 
• Drivers in the .05-.079 range are 5.5 times baseline risk; those above .08 are much riskier (15.5 times baseline). Same study has no increased risk for cannabis, but combinations of alcohol and other drugs were very risky.
• People who are left-handed have 2.35 times baseline accident risk.
• Not including any alcohol-related accidents, time of day matters a lot. Driving at 4 in the morning is 5.7 times as risky for accidents as driving at 10-11 am; they chalk it up to sleepiness. Maybe we should just have curfews.

A few others I've not seen studies about, but surely matter:

• Children in the back seats, by age and number
• Finding a screamed-for child's toy on the floor of the back seat while driving
• Stopping child from kicking the back of the seat
• Resolving disputes about whether it's her turn for music or his turn for audiobooks
• Enforcing bargains made in the back seat by the children with respect to turns
• Driving after child in toilet training in back seat announces "I need to make a pee"
• Note that post-quake Christchurch, with portaloos everywhere, was rather good on this front.
• Indulging a five-year old's preference to dungeon master me through a scenario he's inventing on the go and trying to keep track of the rule changes he keeps making.
• Checking the speedometer every 30 seconds on windy and hilly roads to make sure that you haven't varied by more than 4kph from the speed limit.
• And, finally, Sue Ellen Mishke

Update: Otago's Nick Wilson commented on the same study for the Fairfax papers. He graciously pointed me to the following additions:

• People with latent toxiplasmosis (from cats) have 2.65 times the baseline risk of car accident. That's the average. For those with high levels of toxiplasmosis antibodies, the risk is 16 times higher. People with high levels of toxiplasmosis are worse than people driving above .08. See also here.
• Some of the evidence on risks associated with having a cold, though I haven't the time today to calculate odds ratios from their presented data. See also here.