Drivers are more likely to fall asleep at the wheel on Fridays in November than at any other time of the year, warned the Thames Valley Police.
According to a report, their research said that tiredness was a significant problem as the clocks have only just gone back, and Friday is the end of the working week for the majority of people.
Accidents caused by tiredness peaked at around 3am and were most common on motorways, said the report.
Thames Valley Police Safer Roads Partnership analyst, Bruce Walton, said there were 6% more accidents caused by tiredness of Fridays than the weekly average.
He said figures from the past five years had shown that there were 11% more accidents resulting in injuries during rush hours in the week after the clocks changed, concluded the report.
