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How does alcohol affect a driver, and what are the legal blood-alcohol limits?

The effects of alcohol on driving ability, the legal blood-alcohol limits and BAC, and the consequences of drink-driving.

A CCEA GCSE Motor Vehicle and Road User Studies answer on how alcohol impairs driving, the legal blood-alcohol limits (BAC), and the penalties and dangers of drink-driving.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

CCEA wants you to explain how alcohol impairs driving, state the legal blood-alcohol limit (the BAC), and describe the penalties and dangers of drink-driving. Alcohol is a core road-safety topic and appears in nearly every Unit 1 paper, often combined with drugs and fatigue in an "impairment" question.

The answer

How alcohol affects driving

Alcohol is a depressant: it slows down the brain and nervous system. Even small amounts impair the skills a driver needs.

A dangerous feature of alcohol is that it makes a driver feel more confident while actually being less capable, so they take chances they would normally avoid.

Blood alcohol concentration (BAC) and the legal limit

The legal drink-drive limit in Northern Ireland, England and Wales is 80 mg of alcohol per 100 ml of blood. (Scotland's limit is lower, at 50 mg/100 ml.) There are equivalent limits for breath and urine. Police test BAC at the roadside with a breathalyser, confirmed by an evidential breath, blood or urine test at the station.

There is no reliable way to know how much you can drink and stay under the limit, because it depends on body weight, sex, metabolism, food eaten and the type and strength of the drink. The safest rule is none for the road.

The consequences of drink-driving

Being convicted of drink-driving brings serious penalties:

  • A driving ban (disqualification) - at least 12 months for a first offence.
  • A heavy fine.
  • Penalty points and a criminal record, which can affect employment and insurance.
  • For causing death by careless driving when over the limit, a prison sentence.

Beyond the penalties, the human cost is the real danger: drink-driving is a major cause of serious and fatal collisions.

Worked example: why "I feel fine" is not safe

Examples in context

Example 1. A small drink, a big delay. A driver just over the limit may take a few tenths of a second longer to react, which at 30 mph adds several metres to the thinking distance - enough to turn a near miss into a collision.

Example 2. The morning after. Someone who drank heavily the night before can still be over the limit the next morning, because the body removes alcohol only slowly (roughly one unit per hour).

Try this

Q1. What type of substance is alcohol in terms of its effect on the body? [1 mark]

  • Cue. A depressant (it slows the brain and nervous system).

Q2. State the legal drink-drive limit in Northern Ireland in mg per 100 ml of blood. [1 mark]

  • Cue. 80 mg of alcohol per 100 ml of blood.

Q3. Give two ways alcohol impairs driving. [2 marks]

  • Cue. Any two of: slower reactions, impaired judgement, reduced co-ordination, blurred vision, false confidence, drowsiness.

Exam-style practice questions

Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

CCEA style4 marksExplain four ways in which alcohol impairs a person's ability to drive safely.
Show worked answer →

Any four of the following:

  • Slower reaction time - the driver takes longer to respond to hazards, lengthening the thinking distance.
  • Impaired judgement - of speed, distance and risk, so the driver misjudges gaps and bends.
  • Reduced co-ordination - smooth control of steering, gears and brakes is lost.
  • Blurred or double vision and reduced field of vision.
  • False confidence / increased risk-taking - the driver feels capable while actually being less able, so takes more chances.
  • Drowsiness - alcohol is a depressant and can cause tiredness.

Markers reward four distinct, correct effects.

CCEA style3 marksState the legal drink-drive limit in Northern Ireland expressed as milligrammes of alcohol per 100 millilitres of blood, and give two penalties a driver can face for drink-driving.
Show worked answer →

The legal limit (as used in England, Wales and Northern Ireland) is 80 mg of alcohol per 100 ml of blood (the BAC limit). Note that Scotland uses a lower limit of 50 mg, and proposals exist to lower the NI limit, but the figure tested in CCEA papers is 80 mg per 100 ml.

Two penalties (any two): a driving ban (disqualification); a heavy fine; penalty points; a criminal record; or, for causing death by careless driving when over the limit, a prison sentence.

Markers reward 80 mg per 100 ml of blood plus two valid penalties.

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