It's no secret that people who are tired don't perform well but a new study tackles the impact of being a morning person or a night owl on driving performance.

By measuring people when they are out of sync with their "chronotype" whether they are physiologically more active during the day or night - influences driving performance, and which chronotype performs better at a non-optimal time.

Result: evening-types are much worse drivers at their non-optimal time of day, early in the morning, while morning-types were more stable drivers than evening-types and drove relatively well both in the morning and the evening. The article in Accident Analysis and Prevention by the 'Neuroergonomía' research group of the University of Granada, analyzed the circadian rhythms in a sample of 29 University of Granada students with extreme chronotypes, selected from a database sample of over 500.

Early birds and night owls

Circadian rhythms—from the Latin circa, 'around', and dies, 'day'—are differences in biological variables that occur at regular intervals, such as sleep and wakefulness. "As scientists we use the simile related with birds: we tend to compare early birds—we call them sky larks—with morning-type people, and night owls with evening-types", explains Ángel Correa, principal author of the study.

The University of Granada team used a questionnaire to determine issues such as when participants were most energetic or what their sleeping habits were, and a driving simulator. So, both the morning- and the evening-types were made to drive at 8.00 in the morning and 8.00 in the evening. Then they compared their driving performance at their respective optimal and non-optimal times of day.

In the light of their results, the researchers suggest that businesses should test workers to determine whether they are morning- or evening-types and adapt work schedules to suit chronotypes.

High-risk professions

"Certain professions involve performing tasks that require good attention vigilance—airline pilots, air traffic controllers, supervisors in nuclear power stations, surgeons, or lorry drivers," Correa points out.

"A particular time of day can be a good or a bad time to perform these tasks as a function of the chronotype of the individual involved, although there are times that are bad for everyone, like siesta time or in the early hours between 3.00 and 5.00," he warns.

The University of Granada researchers warn that driving after more than 18 hours wakefulness—say, at 2.00 in the early morning after waking at 8.00 the previous morning, which is quite common—"entails the same level of risk as driving with the legal maximum level of blood alcohol, because our level of vigilance declines considerably."