Symptoms of sleepiness while driving and their relationship to prior sleep, work and individual characteristics

In total, 154 lorry and bus drivers participated in a questionnaire study dealing with sleepiness in traffic. The questionnaire included questions about sleep before work, appearance of sleepiness, the type of sleepiness they experienced while driving, and ways to counter sleepiness while driving. Driver sleepiness was analysed with respect to age, type of driving, traffic intensity, experience of work, and sleep before work. About 14% of the drivers reported regular sleepiness while driving, 33% had occasionally fought sleepiness while driving, and 8% had experienced nodding of the head while driving. The majority of the drivers had once been so tired that they had to stop driving. Sleepiness normally occurred between 03.00 and 06.00, at the end of longer trips, and was most frequently appeared in autumn. Poor sleep and poor working hours were considered as the most important causes to sleepiness. Eye tiredness, yawning, difficulties concentrating on the road, and difficulties keeping one’s thoughts together: these were the most frequently reported symptoms of sleepiness. More sleeping hours before work, better working hours, naps during work, listening to the radio, conversations, and lowering the cabin temperature were the most frequently mentioned countermeasures. The appearances of sleepiness while driving was strongly correlated to lower sleep hours and lower sleep quality before work. Age, type of work, or work experience did not interfere with sleepiness in the investigated group in any systematic way.