By: Brian Frier, MD, FRCPE |Date: Thursday 29 March 2018| Categories: Hypoglycaemia, Driving performance, Insulin-treated, Impaired Awareness

Driving is a complex activity that requires cognitive integrity, and hypoglycaemia impairs cognition across a range of domains. The inevitable result? Impaired driving performance.

Studies certainly bear this out. In one study of patients with type 1 diabetes, 52% of the drivers reported at least one driving mishap over the past 12 months, and 5% reported six or more.Not surprisingly, the risk was higher in people with a history of severe hypoglycaemia and in those who did not measure their blood glucose before getting behind the wheel.1

Another study, which monitored  blood glucose, symptom perception, and corrective actions in patients with type 1 diabetes using a driving simulator, found driving performance was significantly impaired across a range of low glucose levels, including relatively mild hypoglycaemia.2  Anecdotally, impaired awareness of hypoglycaemia (IAH) has also led to road traffic accidents, though most large studies have not identified it as a significant risk.3

In an ideal world, all drivers would stop their car at the first symptom of low blood glucose. The trouble is, many hypoglycaemic drivers do not realise when their driving performance is impaired, and other at-risk individuals may not take the problem seriously enough—for which deficient knowledge among health providers may be partly to blame.4,5 For example, few drivers at risk of hypoglycaemia routinely monitor their blood glucose and some believe it safe to drive even with a blood glucose level below 3.0 mmol/L (54 mg/dL).6

At a societal level, regulations for issuing driving licences to individuals with insulin-treated diabetes may be lacking or inconsistently enforced, particularly in less developed parts of the world.7 Compounding this challenge, individuals who depend on driving to make a living may be tempted to conceal information when answering some assessment questions for fear of losing their licence.8

Taking the high road

Regulators and researchers continue to make efforts to identify drivers at high risk of hypoglycaemia-related driving accidents. As a notable example, U.S. investigators recently developed an 11-question scale called RADD, using self-reported data from over 1,000 individuals with type 1 diabetes.9

At the same time, health providers can help people with diabetes minimise the risks by communicating the following points to their patients:

  • The act of driving itself can cause blood glucose to fall and provoke hypoglycaemia because the brain consumes a significant amount of glucose during driving.10 Drivers should test their blood glucose before driving and consume a prophylactic snack if the level is below 5.0 mmol/L (90 mg/dL).5 If below 4 mmol/L (72 mg/dL), the individual should not drive.5
  • People driving for more than 30-60 minutes should test their blood glucose at regular intervals.11
  • Drivers with insulin-treated diabetes should be made aware that failure to measure blood glucose could have major medicolegal consequences.12
  • People who experience a progressive decline in their awareness of hypoglycaemia should consult a health care provider to assess their fitness to drive.11
  • Particular care should be taken during changes in routine, which range from adjustments in lifestyle or insulin regimen, to travel and pregnancy.

Hypoglycaemia poses a risk to all insulin-treated individuals. Although the magnitude of its effect on driving safety continues to be debated, it undoubtedly can cause road traffic accidents, some of them fatal. That said, people at risk of hypoglycaemia do not necessarily need to hand over their keys. With proper guidance and commitment to following safe driving practices, most insulin-treated drivers can stay safe while on the road.


  1. Cox DJ et al. Driving mishaps among individuals with type 1 diabetes: a prospective study. Diabetes Care 2009; 32:2177-2180.
  2. Cox DJ et al. Progressive hypoglycemia’s impact on driving simulation performance. Occurrence, awareness and correction. Diabetes Care 2000; 2:163-170.
  3. Inkster B, Frier BM. Diabetes and Driving. Diabet Obes Metabol 2013; 15:775-783.
  4. Watson WA et al. Driving and insulin treated diabetes: who knows the rules and recommendations? Pract Diabet Int 2007;24:201-06.
  5. Graveling AJ, Frier BM. Driving and diabetes: problems, licensing restrictions and recommendations for safe driving. Clin Diabet Endocrinol 2015; DOI 10.1186/s40842-015-0007-3.
  6. Graveling AJ et al. Hypoglycaemia and driving in people with insulin-treated diabetes: adherence to recommendations for avoidance. Diabetic Medicine 2004; 21:1014-19.
  7. Beshyah SA et al. A global survey of licensing restrictions for drivers with diabetes. Br J Diabetes 2017;17: 3-10.
  8. Pedersen-Bjergaard et al. The influence of new european union driver’s license legislation on reporting of severe hypoglycemia by patients with type 1 diabetes. Diabetes Care 2015; 38:29–33.
  9. Cox DJ et al. Predicting and reducing driving mishaps among drivers with type 1 diabetes. Diabetes Care 2017; 40:742-750.
  10. Cox DJ et al. The metabolic demands of driving for drivers with type 1 diabetes mellitus. Diabetes/Metabolism Research and Reviews 2002; 18:381-385.
  11. American Diabetes Association. Diabetes and Driving. Diabetes Care 2012; 35 (Suppl 1): S81-S86.
  12. Graveling AJ, Frier BM. Driving and diabetes: are the changes in the European Union licensing regulations fit for purpose? Br J Diabetes 2018; 18::25-31.