Tiredness! a natural explanation to The Grand Rapid “DIP”

Abstract

The present analysis deals with the presumed improved driving skill of car drivers with low blood alcohol concentrations (BACs) compared to the driving skill of sober drivers. Several roadside surveys indicate such a controversial possibility, which is illustrated graphically in “The Grand Rapid Study” (1964) as a relative accident risk curve for driving while intoxicated (DWI). A curve which shows a “DIP” below a baseline accident risk of one for sober drivers in the interval between BACs of 0.01 and 0.04 g/l. Since then, various attempts have been made to show this “DIP” in the otherwise “exponentially” raising curve to be an artificial distortion based on disproportionate demographic subgroups. It is, however, our thesis that the observations of “The Grand Rapid Study” and other roadside surveys are valid, because the presumed mono-causal traffic accident curve hides “tiredness” as an additional human risk factor. This makes the first part of the night-time relative accident risk curve for impaired drivers artificially augmented by “tired” drivers with insignificant amounts of alcohol in the blood and therefore incorrectly accused of accidents due to DWI. The accident risk curve for higher BACs raises similarly abrupt due to drivers impaired by a combined effect of alcohol and “tiredness”. Moreover, to imply an accident risk of one for all sober drivers independent of the time of the day is debatable as an increased accident risk is present in the late night-time hours due to “tired” drivers. This increase in “tired” sober accident drivers suppresses the accident risk curve for DWI with BACs of 0.01–0.04 g/l below the fixed baseline of one for the background population.