The study focused on 14 healthy young men. The participants drove in three nocturnal driving sessions (3-5 a.m., 1-5 a.m. and 9 p.m.-5 a.m.) on an open highway. Inappropriate line crossings in the last hour of driving of each session, sleep variables, self-perceived fatigue and sleepiness were analyzed.
According to the results, compared to the 3-5 a.m. driving session, the incidence rate ratio of inappropriate line crossings increased by 2.6 in the 1-5 a.m. driving session and by 4.0 in the 9 p.m.-5 a.m. driving session. Compared to the reference session (9-10 p.m.), the incidence rate ratio of inappropriate line crossings were 6.0 in the 3-5 a.m. driving session, 15.4 in the 1-5 a.m. driving session and 24.3 in the 9 p.m.-5 a.m. driving session. Self-related fatigue and sleepiness scores were both correlated to driving impairment in the 1-5 a.m. and 9 p.m.-5 a.m. driving sessions and increased significantly during the nocturnal driving sessions compared to the reference session.
“Up to now, regulations have taken into account maximal duration of driving, but the cumulative effects of sleepiness and fatigue were never studied or integrated in the driving regulation,” said Pierre Philip, of Université Bordeaux in France, one of the authors of the study. “Here, we show that performance is badly affected by time of the day, and therefore, we think that a warning to limit maximum nocturnal driving duration should be included in professional safety recommendations.”-American Academy of Sleep Medicine
