1 in 4 seems high, especially if you mean to the level of impairment. I'd be interested to see the source of that statistic.
On Friday and Saturday nights (presumably peak impairment time), checkpoints determine that about 3% of drivers are impaired. http://www.iihs.org/iihs/sr/statusreport/article/48/10/1
FWIW, http://www.allergy.org.au/patients/product-allergy/alcohol-a... says:
> The human body constantly produces small amounts of alcohol itself. Normal levels of 0.01 to 0.03 mg of alcohol/100 ml are contained in the blood. By contrast, a blood alcohol limit for driving of 0.05 per cent is equal to around 50 mg of alcohol/100 ml of blood.
Thus, according to my definition, 100% of drivers have a statistically significant amount of alcohol in their blood system, though nowhere near to the level of impairment.
One in 10^4 would be (much) more accurate.
Source: http://www.dailytelegraph.com.au/news/breaking-news/nsw-poli...