Researchers from the University of Granada have shown that individual chronotype—that is, whether someone is a “night owl” or “early bird”—markedly influences driving performance.

In fact, evening-types are much worse drivers—they pay less attention—at their “nonoptimal” time of day (early in the morning) by comparison with their optimal time (during the evening). However, in this experiment morning-types were more stable drivers than evening-types and drove relatively well in both the morning and the evening.

In an article published in Accident Analysis and Prevention, researchers from the neuroergonomía research group of the University of Granada Mind, Brain and Behavior Center analyzed the circadian rhythms in a sample of 29 University of Granada students with extreme chronotypes, selected from a database sample of over 500.

“As scientists, we use the simile related with birds: we tend to compare early birds—we call them skylarks—with morning-type people, and night owls with evening-types,” says Ángel Correa, principal author of the study, in a release. 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 nonoptimal times of day.

In 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.

“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 of wakefulness—say, at 2 AM after waking at 8 AM 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.”