Objectives-To assess the incidence, time of day, and driver morbidity
associated with vehicle accidents where the most likely cause was the
driver falling asleep at the wheel. Design-Two surveys were undertaken
, in southwest England and the midlands, by using police databases or
on the spot interviews. Subjects-Drivers involved in 679 sleep related
vehicle accidents. Results-Of all vehicle accidents to which the poli
ce were summoned, sleep related vehicle accidents comprised 16% on maj
or roads in southwest England, and over 20% on midland motorways. Duri
ng the 24 hour period there were three major peaks: at around 0200, 06
00, and 1600. About half these drivers were men under 30 years; few su
ch accidents involved women. Conclusions-Sleep related vehicle acciden
ts are largely dependent on the time of day and account for a consider
able proportion of vehicle accidents, especially those on motorways an
d other monotonous roads. As there are no norms for the United Kingdom
on road use by age and sex for time of day with which to compare thes
e data, we cannot determine what the hourly exposure upsilon risk fact
ors are for these subgroups. The findings are in close agreement with
those from other countries.