Objective measurement of sleepiness in summer vacation long-distance drivers

The study investigated whether sleepiness at the wheel is a problem in non-commercial drivers going on summer vacation. All drivers, who stopped at a rest area on a large European freeway while one of the interviewers was available, were systematically approached and asked to respond to a questionnaire. All subjects who had driven at least 400 km (240 miles), whose age was between 20 and 46 years of age, and who agreed to participate were asked to undergo a longer investigation that included a short sleep/wake diary describing overall sleep habits during the year, a sleep/wake log covering the days just prior to departure, an analog visual scale indicating sleepiness at time of interview, and a polygraphically monitored two nap sleep test (TNST). A control group was recruited that consisted of subjects of the same age range, normal sleep habits, and normal nocturnal sleep time before administration of the TNST. One hundred and four drivers (2 women) participated between 08:00 and 20:00 h. The total group was subdivided into 6 subgroups based upon the time of day of their investigation (08:00-10:00 h, 10:01-12:00 h, etc.). The control group included 50 men with 50-55% of control subjects, relative to the total number of index-cases, in each subgroup. Eighty-eight percent (n = 92) of studied drivers had experienced acute sleep deprivation within one day prior to departure due to the planned long driving. The TNST demonstrated that, overall, drivers had a significantly shorter sleep latency in nap 1 and nap 2 than controls, had a significantly longer sleep duration in nap 1 and nap 2, and there was a significant correlation between the sleep debt prior to departure and the sleep stage reached during the TNST. It is concluded that the TNST is a test which allows the objective study of sleepiness in drivers without the burden of the multiple sleep latency test. Many drivers are excessively sleepy when making long summer vacation journeys.