Man drinking from bottleA new study finds that driving while dehydrated is as dangerous as driving while drunk or on drugs, writes The study, conducted at Loughborough University, is published in the journal Physiology and Behavior, as reports. According to the study, “Having as few as five sips of water an hour while driving is equivalent to being over the drink drive limit,” writes Nicola Harley for The Telegraph. And being only mildly dehydrated causes drivers to make more than twice the number of mistakes as those drivers who are hydrated, Harley adds.

Harley writes:

Professor Ron Maughan, Emeritus Professor of Sport and Exercise Nutrition, who led the study at Loughborough University, said: ‘We all deplore drink driving, but we don’t usually think about the effects of other things that affect our driving skills, and one of those is not drinking and dehydration.

‘There is no question that driving while incapable through drink or drugs increases the risk of accidents, but our findings highlight an unrecognised danger and suggest that drivers should be encouraged to make sure they are properly hydrated.’

To conduct the study — which Adam Withnall reports for The Independent is the first to investigate the effects of dehydration on driving ability — researchers tested male volunteers over three days using a laboratory driving simulator, Harley reports. Each volunteer “drove” on the simulator one day while normally hydrated (given 200 ml of fluid per hour, which is 6.76 ounces) and on another day while dehydrated (given only 25 ml of fluid per hour, which is 0.8 ounce). Harley writes:

The simulated driving task included a two hour continuous monotonous drive on a dual carriageway, with bends, a hard shoulder and simulated auditory ‘rumble strips’, and slow moving vehicles which had to be overtaken.

On average, the study participants made 47 driving errors when normally hydrated, but 101 when dehydrated, Withal writes. The number of errors made by the dehydrated drivers is “roughly the same number as someone who has consumed the legal limit of alcohol,” Withnall writes. Harley notes that the legal limit in the United Kingdom is a blood alcohol content of 0.08%. (In Colorado, the legal blood alcohol limit for drivers over 21 years old is 0.08%, while the limit for drivers under 21 years old is 0.02%, according to The errors dehydration can lead to, according to the study, include such things as drifting out of lane, late braking, and touching or crossing the rumble strip or lane line, Harley writes.

The level of the dehydration in the study was mild, Harley writes. It can produce negative changes in mood; headache; fatigue; and reduced concentration, alertness, and short-term memory, according to the study, as Harley writes. The study warns that driving in a hot car can lead to dehydration, especially during a long trip, and can be exacerbated by drivers who purposely limit their liquid intake to avoid bathroom stops, Harley writes.

Image by Ana Ulin

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