Long-distance lorry drivers who drink coffee have fewer road traffic accidents, research suggests.
Australian investigators say they found the link while comparing 530 heavy goods vehicle drivers who had recently been in a crash with 517 who had not.
Coffee and other beverages containing the stimulant caffeine cut crash risk, probably because they boost alertness, the British Medical Journal reported.
Road safety experts stressed caffeine was no substitute for sleep.
In the study, more than a third said they drank caffeinated beverages and half of these said they did so in order to stay awake.
The drivers who consumed caffeine to keep them from nodding off behind the wheel were 63% less likely to crash than drivers who had no caffeine.
This was after adjusting for factors such as age, sleep patterns, kilometres driven, breaks taken and night-driving schedules.
If the driver had a poor track record of crashes in the past five years this had an impact on their likelihood of having another crash, raising their risk by 81%.
About 70% of the drivers in the study said they stopped for a nap when they were tired - something that road safety experts strongly recommend.
Lead researcher Lisa Sharwood and colleagues from the University of Sydney say while it is clear that tired drivers should be taking breaks, it still not clear what activities benefit them most during these breaks - napping or drinking coffee.
"The varying extent to which activities such as taking a nap, drinking a cup of coffee, or going for a short walk contribute to subsequent vigilance behind the wheel are not well understood and are therefore recommended for further study," they say.
UK road safety experts say the only real cure for fatigue is sleep.
A spokesman for the Department for Transport said: "Driving tired significantly increases the risk of an accident so we encourage drivers to ensure they are properly rested before climbing behind the wheel.
"Drivers should get a good night's sleep, plan sufficient breaks and pull over if they feel tired.
"The Highway Code is clear that the most effective way to counter sleepiness while driving is to have, for example, two caffeinated drinks and take a short nap."