Stress and shortage of sleep may cause daytime somnolence and impaired vigilance at the wheel, especially among those suffering from sleep disturbances. According to the international consensus meeting in Stockholm in May of 2000 on "The sleepy driver and pilot--causes, risks and countermeasures", drowsy driving is an underestimated risk factor in official statistics, and as many as 15-30 percent of today's traffic accidents are related to drowsiness; thus it is an even greater risk factor than alcohol. Drowsy drivers suffer from inattention, impaired concentration and may even fall asleep at the wheel. Accidents during dozing result in three times as many fatalities as other accidents. There are a number of reasons for habitual drowsiness at the wheel aside from sleep deprivation, including rhonchopathy, shift work and jet lag, mental depression, insomnia, narcolepsy, endocrinological diseases, periodic limb movement disorder, medication, pain-disordered sleep, and heart disease. Among the most active drivers, i.e. middle aged men, obstructive sleep apnea syndrome (OSAS) has been found to be the most common reason for habitually drowsy driving. OSAS causes a 2-3 fold increased risk of traffic accidents, and it impairs simulated driving. Palatoplasty as well as nasal CPAP have been shown to improve vigilance and driving performance to an extent that the increase in risk is eliminated. Drivers suffering from habitual drowsiness and micro-sleep attacks forcing them to take repeated rests are at special risk. Even if they are as dangerous as drivers with unlawful blood alcohol levels they cannot be caught in a police checkpoint. However they often seek medial advice, and properly treated they may often return safely to traffic. If not, there could be a need to report them to the authorities so as to limit or prohibit their driving.