Driving while sleepy can have devastating consequences, but it is an under-recognised problem often associated with behavioural factors, medical conditions or medications. All drivers have a responsibility not to drive if sleepy and there are DVLA regulations restricting driving for patients with certain sleep disorders who are at risk of excessive sleepiness at the wheel. However, sleepiness can be difficult for patient and doctor to assess and guidelines open to interpretation. As doctors it is important we give consistent and reliable advice to patients who may be at risk when driving. This review suggests how to assess driving risk, educate patients about risk reduction, and clarifies DVLA guidelines in this area.
Sleepiness at the wheel (SATW) is a common but under recognised problem. In the UK, anonymous voluntary surveys indicate 37% of drivers admit sleepiness at the wheel, and 13% admit falling asleep.1 Worldwide, up to 58% admit driving while sleepy.2 Tiredness at the wheel increases the risk of road traffic accidents (odds ratio 2.51),2 with studies suggesting worldwide, between 15-20% of accidents are sleep related.3
As doctors our role is to assess and advise patients about how sleepiness may affect driving ability. This can be difficult since sleepiness is an inherently subjective and variable feeling, and reliable tests to predict or objectively measure levels of sleepiness at any given time are lacking. Driver and Vehicle Licensing Agency (DVLA) guidelines can seem open to interpretation with limited guidance on assessing patients in clinic. We discuss assessment of patients’ risk of sleepiness at the wheel, the responsibilities of patients, doctors and the DVLA and treatment strategies to reduce risk and improve symptoms.
Assessing risk of sleepiness while driving
The aim is to identify drivers who are excessively sleepy at the wheel such that it impairs driving. Taking a detailed history is key. If they feel sleepy while driving enquire how often, and under what circumstances, for example does it depend on duration or time of the journey. Ask specifically about ‘red flag’ symptoms which, if occurring frequently suggest a patient is at high risk of excessive SATW:
- Have they nodded off or had instances of ‘head bobbing’ at the wheel?
- Any near misses including lane crossings, or driving onto rumble strips?
- Any driving accidents or claims on insurance in the last three years?
- Using behaviours aiming to increase alertness such as winding windows down or playing loud music.
- If applicable, for older patients, asking whether they are allowed to drive with grandchildren in the car.
Next it is important to enquire about risk factors that may help to explain patients’ symptoms. Discussing these factors can help patients and clinicians understand driving risk and ways to mitigate future problems. Risk factors for SATW are shown in Box 1.
A collateral history regarding driving and a description from a bed partner of any overnight sleep phenomena are useful.
Box 1: Risk factors for sleepiness at the wheel
|Behavioural causes of acute  or chronic  sleep deprivation from late nights or early mornings due to social, family or work commitments. Worryingly, patients who are chronically sleep deprived may lose insight into their degree of sleepiness and continue to drive despite being excessively sleepy. |
|Driving at times corresponding to circadian dips in alertness, for example overnight or mid afternoon. [3,4]|
|Shift workers . Driving home after working an overnight shift is a particular danger since night shift workers are often sleep deprived. Additionally, drivers have built up a large sleep debt by the end of their shift. Driving in for early morning shifts can be risky especially for younger drivers who may have a natural tendency to a delayed sleep phase.|
|Driving long distances, alone, on monotonous roads. |
|Many medical conditions affect sleep and so doctors from a variety of specialties will see patients who may be at risk of sleepiness at the wheel.|
• Obstructive sleep apnoea8 (OSA). Underdiagnosed and rates are increasing due to rising levels of obesity.  Obstructive sleep apnoea syndrome (OSAS) describes OSA associated systemic features including daytime sleepiness. Also associated with craniofacial structural abnormalities which impair ventilation.
• Central hypersomnias 
• Narcolepsy (may have comorbid OSA)
• Idiopathic hypersomnia
• Sleep deprivation secondary to restless legs and insomnia is often a patient concern but with less evidence for increased crash risk. 
• Parkinson’s disease (may have comorbid OSA, and dopaminergic drugs can cause sleepiness).
• Stroke is commonly associated with OSA.
• Lesions affecting diencephalon and brainstem structures.
|Medications and drugs:|
|Always review medications as drugs are an extremely common cause of sleepiness. Sedative medications, including opiates, benzodiazepines, antipsychotics, antihistamines and gabapentinoids, are often taken in combination.|
Tests of sleepiness
Ideally, any test should accurately predict individual risk of accidents, provide a ‘real time’ measure of sleepiness, and assess response to treatment. Unfortunately current tests lack reliability and show only limited associations at best, with driving risk.12 They should not be used as a sole measure of driving safety. However, assessments are often used to quantify sleepiness and sleep disorder severity. These include:
1. The Epworth Sleepiness Scale (ESS): a routinely used questionnaire assessing daytime sleepiness. Although does have driving related questions, was not designed as a driving safety tool. Scores of >10 are abnormal.
2. The Apnoea Hypopnoea Index (AHI): used for diagnosis and classification of OSA. Those with severe OSA (AHI>30) are more likely to be sleepy.
3. The Maintenance of Wakefulness Test (MWT) measures the ability to stay awake. However the testing environment, a quiet, dimly lit room is far from real life driving situations.
4. Devices which monitor behavioural and physiological variables during simulated or real life ‘in vehicle’ driving have been used in research studies to investigate sleepiness and driving abilities but are not yet reliable enough to predict real life driving safety.12
What advice can I give patients?
First it is important to clarify the patient’s perspective on their symptoms. Patients may need an explanation of how their condition can affect driving. Risks should not be exaggerated but patients need to appreciate that driving while sleepy can have devastating consequences. Drivers should understand that it remains their duty to be alert behind the wheel regardless of whether they are on treatment. Although there is no UK law prohibiting driving while sleepy, if sleepiness is found to contribute to a driving accident, drivers can face imprisonment for dangerous driving.
Educating patients about strategies to reduce SATW can enable patients to feel safer on the road. For example, avoiding driving at night, mid- afternoon or when sleep deprived. If feeling tired on longer journeys, stopping to have a caffeinated drink and a nap does reduce sleepiness, but playing loud music, opening windows, and getting out to stretch does not.4 The DVLA and road safety charity websites provide useful information for patients.13,14 Encourage patients that sleepiness typically improves with treatment. For some, sleep hygiene advice and avoiding risky situations will resolve the problem. Patients with OSA who have daytime sleepiness (Obstructive Sleep Apnoea Syndrome: OSAS) usually need CPAP. Patients with central hypersomnias will need stimulants and treatment of any cataplexy. Scheduled naps for narcolepsy can be helpful.
Do they need to stop driving?
Context is important: excessive sleepiness occurring frequently without an avoidable cause is more concerning than a single episode of sleepiness at the wheel while driving at night which the patient has then avoided doing. Concern from a friend or relative is also worrying.
For patients who have concerning SATW, as part of our duty of care, doctors should advise patients that they should stop driving. As always, the medical board of the DVLA ultimately decide whether a licence should be revoked. Patients need to be aware of the insurance and potential legal consequences of driving against medical advice.
Rarely, a patient continues to drive against medical advice. In this situation, we have support from the GMC to inform the DVLA without patients’ consent although we must inform the patient of our intentions beforehand. 15
Occasionally patients with markedly abnormal sleep study results deny SATW. Some patients genuinely do not feel tired when driving, but in other cases, patients under-report symptoms while admitting easily falling asleep in other situations, because of concern about losing their licence. This discrepancy raises suspicion that the patient could be at risk while driving. A collateral history from a partner can be helpful. Ultimately the patient’s story should be taken at face value but regulations on driving and sleepiness should be discussed and documented.
What are the DVLA guidelines on sleep conditions and driving?
Patients are legally responsible for informing the DVLA if they have certain sleep related conditions (see below) or if they are excessively sleepy at the wheel for three months because of another medical condition. The DVLA will ask them to complete an SL1 (Group I licence holders) or a SL1V form (Group 2 licence holders). Full guidance can be found on the DVLA website.16,17
Obstructive sleep apnoea16
Which patients need to inform the DVLA? Those with moderate or severe OSAS with excessive sleepiness while driving need to inform the DVLA immediately, while those with mild or suspected OSAS causing excessive sleepiness while driving, only need inform the DVLA if symptom control cannot be achieved in three months.
Will the DVLA stop them driving? The DVLA only restrict driving if sleepiness is, or is likely to impair driving, regardless of the AHI.
When can patients return to driving? Patients can resume once there is control of their condition and symptoms have improved. In addition, certainly for those with moderate/ severe OSAS, the DVLA needs evidence that patients are compliant with treatment and agree to be reviewed by their medical team annually (lorry or bus drivers), or every three years (car and motorcyclists).
The advice regarding symptom control can seem ambiguous, but in practice, patients need to feel more awake during the day, with improvements documented by their sleep service.
Patients who start CPAP often feel a benefit almost immediately but most services suggest using it for ≥2 weeks, and ≥70% of the night before considering driving again. The DVLA need to be informed that they are no longer sleepy, but drivers can return to driving before a DVLA decision if supported by their medical team. The British Thoracic Society provides guidance in this area.18
Which patients need to inform the DVLA? All patients diagnosed with narcolepsy or idiopathic hypersomnia need to inform the DVLA at diagnosis.
Will the DVLA stop them driving? Yes; all patients need to stop driving at diagnosis for at least three months.
When can patients return to driving? They can drive if symptoms remain satisfactorily controlled for at least three months. Advice on assessing this is vague, but patients should be free of excessive sleepiness that is likely to impair driving, and should not drive if they have little or no warning about falling asleep (so called ‘sleep attacks’). Formal criteria regarding disabling cataplexy are lacking and this is usually based on clinical impression, but several attacks a day would be concerning. Other requirements: Patients should adhere to medical advice regarding treatment of their condition and remain under regular medical review.
Patients prescribed amphetamines should be aware these are on the DVLA’s list of ‘prescription’ drugs that police can test for if suspecting driving is affected by medications (see below). Patients may wish to carry medical documentation about their condition when driving.
Drugs and driving
In the UK drivers can face prosecution if driving is impaired by legal (prescribed or ‘over the counter’), or illegal drugs.19 Even if driving is not impaired, it is an offence to drive haven taken illegal drugs or certain ‘legal’ drugs (listed by the DVLA including amphetamines, certain benzodiazepines and opioids) without a valid prescription. For patients prescribed amphetamines and opioids, the upper legal limit is higher than would be expected if these drugs were taken at a medically prescribed dose. However, for benzodiazepines and some ‘z’ drugs, patients may pose a driving risk with therapeutic plasma drug levels. This risk is magnified if drugs are taken in combination or with alcohol.20
Summary and conclusion
SATW is a common symptom with potentially tragic consequences. Public health campaigns have helped highlight risks, but it remains an under-appreciated problem. As healthcare professionals, it should be a routine question in clinic with anyone who might be sleepy during the day. We need to understand legislation in the area to provide clear and consistent advice to patients. Encouraging patients to seek help in the knowledge that once treated they will be able to return to driving is key.
- The AA Charitable Trust. Drowsy Driver. Available at: https://www.theaa.com/about-us/aa-charitable-trust.
- Bioulac S, Micoulaud-Franchi J-A, Arnaud M et al. Risk of motor vehicle accidents related to sleepiness at the wheel: A systematic review and meta-analysis. Sleep 2018;41. https://doi.org/10.1093/sleep/zsy075
- Akerstedt T. Consensus statement: fatigue and accidents in transport operations. J Sleep Res 2000;9:395. https://doi.org/10.1046/j.1365-2869.2000.00228.x
- Stutts JC, Wilkins JW and Vaughn BV. Why do people have drowsy driving crashes? Input from drivers who just did. AAA Foundation for Traffic Safety 1999. Washington. https://doi.org/10.1037/e363922004-001
- Philip P, Chaufton C, Orriols L et al. Complaints of poor sleep and risk of traffic accidents: A population-based case-control study. PLoS One 2014;9(12):e114102. https://doi.org/10.1371/journal. pone.0114102
- Gottlieb DJ, Ellenbogen JM, Bianchi MT et al. Sleep deficiency and motor vehicle crash risk in the general population: a prospective cohort study. BMC Med 2018;16:44. https://doi.org/10.1186/s12916-018-1025-7
- Akerstedt T. Shift work – sleepiness and sleep in transport. Sleep Med Clin 2019;14:413-421. https://doi.org/10.1016/j. jsmc.2019.07.003
- Tregear S, Reston J, Schoelles K et al. Obstructive sleep apnea and risk of motor vehicle crash: systematic review and meta-analysis. J Clin Sleep Med 2009;5:573-81. https://doi.org/10.5664/jcsm.27662
- Benjafield AV, Ayas NT, Eastwood PR et al. Estimation of the global prevalence and burden of obstructive sleep apnoea: a literature- based analysis. Lancet Respir Med 2019;7:687-698. https://doi.org/10.1016/S2213-2600(19)30198-5
- Pizza F, Jaussent I, Lopez R et al. Car crashes and central disorders of hypersomnolence: A French study. PLoS One 2015; 10(6):e0129386. https://doi.org/10.1371/journal.pone.0129386
- Liu S-Y, Perez MA, Lau N. The impact of sleep disorders on driving safety – findings from the second strategic highway research program naturalistic driving study. Sleep 2018;41. https://doi.org/10.1093/sleep/zsy023
- Dwarakanath A and Elliott MW. Assessment of sleepiness in drivers: current methodology and future possibilities. Sleep Med Clin 2019;14:441-451. https://doi.org/10.1016/j.jsmc.2019.08.003
- Driver and Vehicle Licensing Agency. Tiredness can kill: advice for drivers (INF159). Available from: https://www.gov.uk/government/publications/tiredness-can-kill-advice-for-drivers
- Brake, the road safety charity. Driver fatigue. Available from: https://www.brake.org.uk/get-involved/take-action/mybrake/knowledge-centre/driver-fatigue
- General Medical Council. Confidentiality: patients’ fitness to drive and reporting concerns to the DVLA or DVA. Available from: https://www.gmc-uk.org/ethical-guidance/ethical-guidance-for-doctors/confidentiality—patients-fitness-to-drive-and-reporting-concerns-to-the-dvla-or-dva
- Driver and Vehicle Licensing Agency. Excessive sleepiness – including obstructive sleep apnoea syndrome. Published March 2016, updated Jan 2018. Available from: https://www.gov.uk/guidance/miscellaneous-conditions-assessing-fitness-to-drive#excessive-sleepiness–including-obstructive-sleep-apnoea-syndrome
- Driver and Vehicle Licensing Agency. Primary/central hypersomnias including narcolepsy type 1 and type 2 (narcolepsy with cataplexy). Published March 2016, updated Jan 2018. Available from: https://www.gov.uk/guidance/neurological-disorders-assessing-fitness-to-drive#primarycentral-hypersomnias—including-narcolepsy-type-1-and-type-2-narcolepsy-with-cataplexy
- British Thoracic Society. Position statement on driving and obstructive sleep apnoea (OSA) 2018. Available from: https://www.brit-thoracic.org.uk/quality-improvement/clinical-resources/sleep
- Driver and Vehicle Licensing Agency. Medication effects. Published March 2016, updated Jan 2018. Accessed on 25/9/20 at: https://www.gov.uk/guidance/miscellaneous-conditionsassessing-fitness-to-drive#medication-effects
- Wolff K, Brimblecombe R, Forfar JC et al. Driving under the influence of drugs. Report from the expert panel on drug driving. Department for Transport. HMSO 2013