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Can naps and caffeine cut risk of driving while tired?

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Driving when tired is a key factor in as many as one-in-five road accidents. But how does being tired influence driving behaviour and what can be done to reduce or avoid the chances of being involved in an incident?

One of the ways in which fatigue impairs driving behaviour is by making reaction times slower.

In one study, 240 male drivers were stopped between 1am and 6am. They were asked to rate how tired they were and to complete a simple reaction time task. Those who felt rested had reaction times of around 189 milliseconds (ms), but those who were very tired had significantly slower reaction times of 309 ms.

However, some research suggests that this increase in reaction times might not be seen in actual driving behaviours. Instead, it is argued that when fatigued and driving, we allocate our resources in such a way that we prioritise collision avoidance, but that other tasks, such as steering accuracy, may suffer.

Regardless of why fatigue influences driving behaviour, it is clear that the chances of having a crash increases greatly when the driver is tired. The important issue is how this risk can be avoided or minimised.

Two psychologists, Reyner and Horne, have conducted a series of experiments examining how effective various methods of reducing fatigue are. Methods such as listening to loud music or opening the window are only effective for a very short period of time, around 15 minutes.

Similarly, a highly-caffeinated drink only relieved sleepiness for about 30 minutes in people who had no sleep at all the night before, although it was more effective if people had at least some sleep. The researchers concluded that the most effective method was to take a nap of just 10 to 15 minutes and then have a caffeinated drink.

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