Driving & Type 1 Diabetes — FAQ

Updated: 9 September 2025

This FAQ supports the Episode 16 page Driving with T1D — 5 to Drive

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?

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.)

External resources (authoritative)