Drivers should consider taking a break when they start to blink more than normal behind the wheel of the car.
That is the advice of road safety champions Gem, which warned that an increase in your blinking rate is a reflex action designed to warn the human body that we are tired and could need sleep.
An increase in the normal blink rate of about ten blinks (referred to by scientific boffins as nictating) per minute is a warning sign that it is time to find an appropriate place to pull over and take a rest from the stress of driving.
The chief executive of Gem, David Williams, said: "Blinking is a built-in early warning system that gives us the opportunity to head for the nearest motorway service area or other refuge from the road before our driving becomes erratic and potentially dangerous.
"It not only tells us that we are getting tired, but we are bored and liable to lose concentration."
The Highway Code advises drivers to take a 15-minute rest after two hours on the road.