Traffic accidents are one of the major worldwide causes of death among individuals aged between 5 and 50 years. The death rate on the roads in the European Union (EU) is 52 deaths per million inhabitants, and in economic terms have been estimated to account for 1%–3% of the GDP of the respective countries, representing up to 500 billion dollars on a worldwide level.1

There is clear evidence that sleepiness, irrespective of its cause, is a significant risk factor for traffic accidents, although it is difficult to determine the exact figures. The National Highway Traffic Safety Administration calculates that 2.5% of fatal accidents and 2% of non-fatal accidents are related to sleepiness, although these numbers may be underestimated.2

Sagaspe et al.3 conducted a telephone survey among 4774 drivers, and found that 5.8% of the respondents had had an accident, 3.2% of which were related to sleepiness.

In a Spanish study of 4002 vehicle drivers, 3.6% regularly experienced sleepiness when driving; of these, 81% had fallen asleep at the wheel at some time, and 25% regularly did so. One of the main causes of habitual sleepiness while driving was sleep apnea.4

Goncalves et al.5 also provided interesting data associated with the prevalence of sleepiness and driving in Europe: in 12434 questionnaires completed in 19 EU countries, the mean prevalence of “falling asleep at the wheel in the last 2 years” was 17%, and of these, the median accident rate was 7% (3.2% of which were fatal).

Sleepiness among professional drivers is a particularly sensitive issue, in view of the possible consequences.6

The population at high risk of experiencing sleepiness at the wheel includes not only professional drivers, due to their longer times of exposure, but also people who work very long shifts or who drive at night, individuals who drive in a state of sleep deprivation, especially young people, or who sleep less than 6h, patients taking hypnotic drugs or other sleep-inducing medications, and finally, individuals with symptoms associated with undiagnosed sleep apnea.7

Various diseases, such as diabetes mellitus, cardiovascular diseases, psychiatric and neurological diseases, obesity or impaired vision, are associated with a higher incidence of traffic accidents,8 but sleep apnea–hypopnea syndrome (SAHS) is the disorder that most frequently causes sleepiness and an increased risk of accidents. Poor sleep hygiene must be added to this group of diseases.

A systematic review and metaanalysis9 of the risk of accidents among drivers of commercial vehicles published in 2009 showed that the mean risk was in the range of 1.21–4.89, and that the predictive factors for accidents among drivers with SAHS include body mass index (BMI), apnea–hypopnea index (AHI), oxygen saturation, and possibly daytime sleepiness. Young et al.10 showed that individuals with an AHI>5 were significantly more likely to have at least 1 accident in a 5-year period, and that men and women with AHI>15 had significantly more multiple accidents in the same period (odds ratio: 7.3).

Although the published studies differ, most of the evidence suggests that the risk of traffic accidents and sleep apnea is related more closely with sleepiness than with disease severity measured by AHI. The significance of sleepiness as a primary factor contributing to traffic accidents was recently supported by Karimi et al.11 who found that excessive daytime sleepiness (Epworth scale>15) is significantly associated with accident rates. Other studies, meanwhile, such as those of Terán-Santos et al.12 and the European Sleep Apnea Database (ESADA), associate AHI with accident rates.13

Several studies have evaluated the effect of continuous positive airway pressure (CPAP) on reducing motor vehicle accident rates in patients with SAHS, and in most studies, effective treatment will result in a substantial reduction or even normalization of the accident rate.14

The fact that untreated SAHS patients have a higher risk of traffic accidents has prompted some countries in the EU, including Spain, to list this disease among those that must be controlled before a driving license can be obtained or renewed. More recently, the EU Commission Driving License Directive 2014/85,15 modifying Directive 126/2006, has included SAHS among the criteria that appear in Annex III on the criteria for psychophysical aptitudes that must be evaluated in all Member States. This regulation was published in the EU in June 2014 and sets down the minimum criteria that must be applied in all countries.

Spain, which already included SAHS in the General Regulations for Drivers, specifically in Annex IV, specifying criteria for psychophysical fitness for obtaining or renewing a driver's license, has updated their criteria in accordance with the European Directive with Royal Decree (RD) 1055/2015, 20 November 2015, modifying the General Regulations for Drivers approved by Royal Decree 818/2009, 8 May 2009, that became effective in January 2016 (Table 1). The annex regarding obtaining or renewing a driving license now includes criteria for moderate (AHI 15–29) and severe (AHI>30) SAHS, both associated with excessive sleepiness, and establishes that individuals with SAHS (diagnosed in a Sleep Unit [SU]) with an AHI of 15 or more associated with sleepiness cannot obtain or renew their driving license, unless they submit a favorable report from the SU stating that they comply appropriately with treatment and that their disease is clinically controlled to a satisfactory degree, particularly with regard to sleepiness. The period of validity of these licenses is limited to 3 years for group 1, and up to 1 year for group 2.

Studies in SAHS and driving show that the risk of a traffic accident in subjects with a diagnosis of SAHS depends not only on the diagnosis of the disease, but also on the different parameters that are also associated with a greater driving risk, and which might affect an individual's fitness to drive.13 This requires a personalized evaluation of the driver in Driving Examination Centers (DACs) and, consequently, the medical staff of these centers must be fully apprised of the impact of the disease on the subject before issuing the psychophysical fitness report.

Annex IV of the General Regulations for Drivers, RD 818/2009, modified by RD 1055/2015, states that to obtain or renew a driving license, drivers with a diagnosis of SAHS must provide the DAC with a report from an SU, which is taken into account in the definitive report on the individual's fitness to drive. The aim of the SU report is to inform the DAC physician of the diagnostic details, clinical manifestations of the disease (primarily sleepiness), and efficacy of treatment, so that the impact of the disease on driving can be evaluated and a report on the fitness of the subject to drive issued. Both the patient and doctors working in SUs must be aware of the need to present this report to the DAC at the time of either obtaining or renewing a driving license, since failure to present the report at the time of license renewal will lead to suspension of the process until such time as it is presented, with the consequent personal and professional inconveniences that such a situation may cause the driver.

Individuals who need to renew their driving license may face difficulties and variable access to SUs, depending on their healthcare areas, our group recommends that a standardized report template is issued for the purposes of obtaining and renewing a license, and that the patient is informed of the importance of such a report and their obligation to present it to the DAC. This report should be valid for a period of 6 months, unless the DAC detects any changes when administering their standard questionnaire.

During the course of their work, the DAC sees 2 large groups of drivers: those with a diagnosis of SAHS, and those without, but who, after clinical screening, are found to meet the established criteria for a high diagnostic suspicion of SAHS.

Excessive sleepiness affects 5%–20% of the population. This problem, together with fatigue, increases the risk of traffic accidents. In total, 3.6% of drivers habitually experience sleepiness while driving.

SAHS is the treatable medical condition most commonly associated with traffic accidents caused by sleepiness.

There is an individual relationship between hours slept and the development of excessive daytime sleepiness.

The population at high risk of experiencing sleepiness at the wheel includes not only professional drivers who have longer times of exposure, but also people who work very long shifts, individuals who drive in a state of sleep deprivation, especially young people, or who sleep less than 6h, patients who use alcohol, hypnotic drugs or other medications that can cause sleepiness, and finally, individuals with symptoms associated with undiagnosed sleep apnea or other sleep disorders.

Every effort should be made to raise awareness of the importance of respecting rest times among professional drivers, so that work interests do not put the safety of drivers or other road users at risk.

Treatment of patients with sleep apneas reduces the number of accidents and associated costs.

The editorial team of these guidelines on procedures in sleep apnea and driving states that the content of this paper is based on current levels of scientific knowledge and that the rate of accidents caused by sleep apneas depends on multiple variables associated with the presence of comorbidities and lifestyle, among other factors.

The authors state that they have no conflict of interests.

Spanish Sleep Society (SES).

Spanish Society of Pulmonology and Thoracic Surgery (SEPAR).

Instituto Carlos III, CIBEReS.

Spanish Traffic Medicine Society.

Spanish Ministry of Health, Social Services and Equality.

General Subdepartment of Road Policies, General Department of Traffic.