Updated: 9 September 2025
This FAQ supports Episode 16, Driving with T1D — 5 to Drive
This FAQ for Group 1 and Group 2 drivers captures the essentials.
Ep-16-Driving
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 → snack, recheck 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 license 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 & monitoring rules (see below).
Monitoring & testing
CGM, flash and finger-prick — what counts for driving?
- Group 1 → CGM/Flash or finger-prick both accepted for pre-drive and in-journey checks.
- Group 2 → finger-prick only for pre-drive and in-journey checks (CGM 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 + strips in the car (spare-tyre mindset).
- Ensure date & time are correct (legal/forensic review depends on it).
- Use NHS-recommended meters/strips; swap out non-recommended devices.
What’s the best CGM for driving tips?
Severe hypoglycaemia & legal duties
What is severe hypoglycaemia?
- An event requiring help from another person to recover.
When you must 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 & treat immediately.
- Confirm > 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 ≤ 2-hour intervals.
- CGM/Flash or finger-prick acceptable for checks.
- No more than one severe hypo while awake in 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 carbs & backup meter (date/time correct).
- Don’t rely on hearsay — read the rules yourself.
Training & 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 every 2 hours while driving; many operators require regular daily records.
- Any severe hypo in 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 top accuracy and top tips?
- Use NHS-recommended meters/strips and keep downloadable records.
- Ensure meter clock is correct; calibrate your process across depots/vehicles.
Cognitive impact & awareness (what the science says)
How muck does hypoglycaemia impairs 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?
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 & 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 min/day) — a small, physiological amount. Use patterns + symptoms, not single data points.
Practical driving setup
What’s the best pre-drive routine
- Pre-drive glucose ≥ 5.0 mmol/L; have 10-20g rapid carbs if 4.0-5.0 mmol/L.
- Re-check at ≤ 2 hours; set CGM low alert to 5.0 mmol/L for longer trips.
- Bring backup meter + strips; verify date/time today.
What about long-journeys?
- Schedule fuel/food stops aligned to ≤ 2-hour checks.
- If you treat a low: confirm >5mmol/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 3rd 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. See 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?
Form wording about awareness at “4 mmol/L”
- Teaching point: 4 mmol/L is an alert, not “true” hypo; many won’t feel symptoms at 4 unless falling. Consider phrasing like: “If your glucose is < 4 and falling, do you still have awareness and symptoms?” (Local form wording; DVLA bar is loss of awareness, not the alert threshold itself.)
How often do people detect < 3.0 mmol/L
- Detection varies widely; consistent finding is incomplete awareness and IAH ~15–30% in modern cohorts (lower with CGM). Avoid claiming a fixed percentage unless your data are published; list IAH screening and education plans.
Healthy people below 4 mmol/L on sensors
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 with clinical judgement in occupational medicine.)
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