Updated: 9 September 2025
This FAQ supports Episode 16:
Driving with T1D — 5 to Drive.
This
FAQ (PDF)
for Group 1 and Group 2 drivers captures the essentials in one place.
Basics
Why you need to be 5 to drive
- Be ≥ 5.0 mmol/L before you start the engine.
- 4.0–4.9 mmol/L → have a snack, re-check if needed, then drive.
- < 4.0 mmol/L → treat hypo → confirm > 5.0 mmol/L → wait 45 minutes before driving.
- The wait exists because cognitive and reaction-time recovery lags glucose recovery.
Why the 45-minute rule?
- After treating a hypo and once > 5.0 mmol/L, wait 45 minutes before driving again.
- This covers the worst-case lag in attention, processing speed, and reaction time after neuroglycopenia.
What are the Group 1 vs Group 2 licence distinctions?
- Group 1 = cars/motorcycles (≤ 3.5 t; ≤ 8 passengers).
- Group 2 = HGV, buses, minibuses (> 3.5 t or > 8 passengers).
- Group 2 has stricter medical and monitoring rules (see below).
Monitoring & testing
CGM, flash and finger-prick — what counts for driving?
- Group 1 → CGM/Flash or finger-prick are both accepted for pre-drive and in-journey checks.
- Group 2 → finger-prick only for pre-drive and in-journey legal checks (CGM is not yet accepted for the legal checks).
How often to check before and when driving?
- Check before you drive and at least every 2 hours while driving.
- Think of each check as a parking ticket that expires after 2 hours — then re-check.
What backup meter and time-stamp discipline do I need?
- Keep a backup meter and strips in the car (spare-tyre mindset).
- Ensure date and time are correct (legal/forensic review depends on it).
- Use NHS-recommended meters/strips; swap out non-recommended devices.
What are the best CGM practices for driving?
- Set a low alert at 5.0 mmol/L for long journeys.
- Use these performance and selection guides to match device to your needs:
Severe hypoglycaemia & legal duties
What is severe hypoglycaemia?
- An event requiring help from another person to recover.
When must you tell DVLA?
- Group 1 → more than one severe hypo while awake in the last 12 months → must stop driving and notify DVLA.
- Group 2 → any severe hypo in the last 12 months → must stop driving and notify DVLA.
If a hypo happens while driving?
- Pull over safely and treat immediately.
- Confirm glucose is > 5.0 mmol/L.
- Wait 45 minutes before you drive again.
Group 1 rules (cars, motorcycles)
Minimum requirements for Group 1?
- ≥ 5.0 mmol/L before driving; re-check at intervals of no more than 2 hours.
- CGM/Flash or finger-prick are acceptable for checks.
- No more than one severe hypo while awake in the last 12 months.
- Adequate hypo awareness retained.
Good practice from Episode 16?
- “Every check expires” → re-check at 2 hours on long journeys.
- Carry rapid-acting carbohydrate and a backup meter (date/time correct).
- Do not rely on hearsay — read the rules yourself.
Training and tech that may help?
Group 2 rules (HGV, buses/minibuses)
Minimum requirements for Group 2?
- Finger-prick testing only for pre-drive and in-journey legal checks.
- Check no more than 2 hours before the start and then at least every 2 hours while driving; many operators require regular daily records.
- Any severe hypo in the last 12 months → must not drive; notify DVLA.
- Full hypo awareness is required; loss of awareness is a bar to Group 2.
Blood glucose meter accuracy and top tips?
- Use NHS-recommended meters/strips and keep downloadable records.
- Ensure the meter clock is correct; standardise your process across depots/vehicles.
Cognitive impact & awareness (what the science says)
How much does hypoglycaemia impair cognition?
- Hypoglycaemia acutely reduces attention, processing speed, and
coordination; impairment can persist 30–45 minutes after glucose normalises → the basis of the 45-minute rule.
How much does hyperglycaemia impair performance?
- Acute hyperglycaemia (for example, ~16.5 mmol/L clamps)
slows information processing and working memory and worsens mood (evidence strongest in type 2 diabetes; applicability to type 1 varies). -
Review articles conclude
hyperglycaemia may affect driving-relevant cognition, but direct on-road data are limited. Use judgement at high levels, especially with marked symptoms or blurred vision.
Alert values vs “true” hypoglycaemia?
- International consensus: < 3.9 mmol/L (70 mg/dL) = Level 1 (alert); < 3.0 mmol/L (54 mg/dL) = clinically significant hypoglycaemia. Use this language in education and forms.
How common is “below 4” in people without diabetes?
- Healthy adults wearing CGM show median ~1.1% time < 3.9 mmol/L (about 15 minutes/day) — a small, physiological amount. Use patterns plus symptoms, not single data points.
Practical driving setup
What is the best pre-drive routine?
- Pre-drive glucose ≥ 5.0 mmol/L; have 10–20 g rapid-acting carbohydrate if 4.0–5.0 mmol/L.
- Re-check at intervals of no more than 2 hours; set CGM low alert to 5.0 mmol/L for longer trips.
- Bring a backup meter and strips; verify date and time on the device.
What about long journeys?
- Schedule fuel/food stops aligned to 2-hour (or more frequent) glucose checks.
- If you treat a low: confirm > 5.0 mmol/L, wait 45 minutes, then continue.
Questions people with T1D actually ask
Driving after a night hypo?
- If you had an overnight low, the 45-minute rule once above 5.0 mmol/L still applies.
Can I rely only on CGM?
- Group 1: yes, for the legal checks, but carry a meter for confirmation and for tech failures.
- Group 2: no — you must finger-prick for legal checks.
What counts as “more than one” severe hypo for Group 1?
- Two or more events while awake in 12 months that require third-party assistance → must notify DVLA and stop driving until assessed.
Do nocturnal severe hypos count?
- DVLA wording emphasises “while awake” for Group 1 recurrent severe hypos; any severe hypo is a bar for Group 2. Always check the DVLA pages for exact wording and latest updates.
Can my clinician “ban” me from driving?
- Responsibility sits with the driver. Clinicians advise, but legal notification is your duty under DVLA rules.
Clinician FAQs
Cognitive impairment at high glucose — what do we know?
-
Acute hyperglycaemia (~16–17 mmol/L clamp)
slows information processing and working memory
in lab settings (mainly type 2 diabetes evidence). Effects are heterogeneous and individual; use clinical judgement for Group 2 safety.
Form wording about awareness at “4 mmol/L”
- Teaching point: 4 mmol/L is an alert, not “true” hypoglycaemia; many will not feel symptoms at 4 unless glucose is falling. Consider phrasing like: “If your glucose is < 4 and falling, do you still have awareness and symptoms?” (Local form wording; the DVLA bar is loss of awareness, not the alert threshold itself.)
How often do people detect < 3.0 mmol/L?
-
Detection varies widely; a consistent finding is incomplete awareness and
impaired awareness of hypoglycaemia ~15–30% in modern cohorts (lower with CGM). Avoid claiming a fixed percentage unless your data are published; list IAH screening and education plans instead.
Healthy people below 4 mmol/L on sensors
- CGM in healthy adults shows ~1% time below 3.9 mmol/L; interpret context and symptoms rather than isolated values.
Evidence base for the 45-minute rule
- Driving reviews and experimental work show cognitive recovery lag of ~30–45 minutes post-hypo → underpinning “wait-to-drive” advice. Use this with clinical judgement in occupational medicine.
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