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Legal guide to UK motoring, sections for law enforcement, Driver licensing, learner and new drivers, buying and selling, speeding fines, owning a vehicle, wheel clamping, traffic information.


Drink-driving: Introduction

Drink driving in the UK is defined as the act of driving a motor vehicle (car, truck, etc.) while under the effects of alcohol. Otherwise known as Driving under the Influence [DUI] or Driving While Intoxicated [DWI], it can become a criminal offence when a subject is caught with blood levels of alcohol in excess of a legal limit.

The UK’s Blood Alcohol Concentration [BAC] limit is 0.8 milligrammes of ethanol per millilitre of blood, as set in the Road Safety Act 1967. A conviction for drink driving may not necessarily involve driving the vehicle; you can also be prosecuted in charge of a parked vehicle and/or failing to cooperate with the police in taking a preliminary roadside breath test.

Alcohol unit calculator

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As well as being against the law, drink driving in excess has also scientifically been shown to greatly increase the risk of injury to all parties on the road. Despite a steady decline in numbers of drink driving accidents, in the UK each year thousands of people are injured on the roads by drivers who drink. Therefore, measures have been and will continue to be taken by successive Governments to lower the rate of casualties and fatalities for all drivers, riders, passengers and pedestrians. This includes the introduction of policies such as the High Risk Offenders Scheme, a series of state-sponsored anti- drink drive campaigns and proposals to give the police indiscriminate powers to breathalyse all vehicle drivers and riders at the roadside.

Drink-driving and the law
Legal Limits: UK
The legal blood alcohol limit for driving is 80 milligrammes of alcohol (80mg) for every 100 millilitres of blood, equivalent to 35 microgrammes of alcohol in 100 millilitres of breath, or 107 milligrammes of alcohol in 100 millilitres of urine. However, prosecution guidelines followed by police services mean that in practice drivers are not normally prosecuted until they reach 40 microgrammes of alcohol per 100 millilitres of breath, equivalent to over 90mg.

Ever since the introduction of the breathalyser in 1967, official sources have been extremely unwilling to publish any figures on the amount of alcohol you need to consume to take you over the 80 mg legal limit for driving. The reason for this is that they feel it will encourage drivers to "drink up to the limit". But, in reality, nobody can do that, because of the extremely unpredictable rate at which alcohol is absorbed by the body. Either you play safe, and stay well below it, or you try to drink up to the limit, and run a serious risk of exceeding it.

Of course, everyone knows that the law lays down a limit, not a prohibition, and that a certain amount of alcohol can be consumed without taking drivers outside the law. This is expressed in the popular wisdom that the limit equals two pints. This can be misleading, but contains some truth. Broadly speaking, if a man of average weight consumes two pints of ordinary strength beer of 4% ABV or less, it is extremely unlikely to take him above the 80 mg legal limit, and in reality will probably lead to a maximum BAC of no higher than 60 mg.

The following is an attempt to express this in rather more detail. It is drawn from various sources, including individuals’ experiences of being breath tested, but the primary source is a booklet entitled The Facts about Drinking and Driving, published by the Transport and Road Research Laboratory in 1986, which presumably can be regarded as reasonably authoritative. However, these guidelines are not a statement of fact, and must not be taken as a guarantee of keeping below the legal limit in any particular circumstances.

Alcohol is normally measured in "units" of 10ml of alcohol. This is the amount of alcohol contained a a half-pint of beer of 3.5% ABV, a single 25ml pub measure of spirits, or a small 125ml glass of light table wine.

The rate of absorption of alcohol into the bloodstream is unpredictable and depends on a number of factors such as the level of hydration, the type of alcoholic drink consumed and whether food is eaten at the same time. As a broad rule of thumb, the alcohol in a drink is fully absorbed about an hour after the drink is finished.

The rate at which alcohol is metabolised and removed from the bloodstream is rather more predictable, and averages out at one unit per hour, starting one hour after the first drink is finished. However, the capacity of the body to metabolise alcohol is finite, and is limited to about 16-20 units per day. If you consistently drink around or above this level, you will probably never be below the limit - and you also need to consider seriously whether you have a drink problem!.

To ensure you run no risk of being "over the limit":
Immediately before driving: - men should consume no more than 4 units, women no more than 3
When drinking the night before driving: - men should consume no more than 10 units, women no more than 7. (This assumes that no alcohol is consumed after 11.30 pm, and that driving does not take place before 8 am the following morning)
This applies to people of average weight (around 12-13 st for men, 9-10 st for women). If you are particularly small, these figures should be reduced accordingly. But if you are particularly big, it is no guarantee that they can be increased. The figures are lower for women not only because they are usually lighter than men, but also because their metabolism is different.

If you drink more than this, it will not guarantee that you will exceed 80 mg, as the rate of absorption of alcohol is so unpredictable. But even with one unit more you will be running a tangible risk. The above figures are the maximum you can consume without any significant risk of exceeding the legal limit, and also without resulting in any significant increase in accident risk.

It is also important to remember that a half pint of beer or a glass of wine can contain considerably more than one unit. Given that most pubs serve draught beer 5 to 10% under measure, it is fairly safe to assume a half of any beer up to around 4% represents one unit. But, any higher than that, and you have to make adjustments. A pint of 5% beer is almost three units, and even one and a half pints may not quite be safe.


Figure 1: Legal BAC limits in the 27 EU Member States
Legal Limits: European Union
As of January 2012, the UK has the highest Blood Alcohol Concentration [BAC] limit fo motorcar drivers out of all 27 Member States, a figure matched only by Malta.2 Figure 1 displays a list of BAC limits for EU countries, expressed in milligrammes of ethanol per millilitre of blood.

Alcohol myth buster

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Under the Road Traffic Act 1988, the following acts are deemed illegal and are given the following penalties:
Figure 2: Drink driving Offences

Offence codes DR10 to DR30 must stay on a driving licence for eleven years from date of conviction. Offence codes DR40 to DR70 must stay on a driving licence for four years from date of offence.

Under the amendments made to the Act in 1991, a drink-driver may be prosecuted in the event of a fatality arising from a motoring accident. These offences are given the CD code, which stands for 'Careless Driving'.

Current legislation contains provision for serious, including repeat, drink-drive offenders to be made to retake the driving test at the end of their period of disqualification, courtesy of the Road Safety Act 2006. It also makes provision for the courts, when imposing disqualification as a penalty, to order a reduced period of disqualification if it also makes an order requiring the offender to comply with the conditions of an alcohol ignition interlock programme. According to the latest annual data from the Ministry of Justice, the number of driving offences committed under the influence of alcohol and/or drugs in England and Wales was estimated to be 54,936 in 2011, down from 58,721 the year before.

The most common offence – driving with alcohol in the blood above the prescribed limit – accounted for at least 9 out of every 10 drink and drug driving convictions (50,051). Young drivers – classified as those between the ages of 17 and 30 – committed the most number of offences (22,536). The fewest drink and drug driving convictions of people of driving age occurred in the 60 and over age group (2,811). Men committed 45,754 offences in 2011, accounting for 83% of all convictions.

A recent Parliamentary question to the Secretary of State for Justice asked how many people have been convicted of offences of drink-driving in each of the last 5 years (see Figure 4).3 In 2011, 50,622 people were proceeded against at magistrates courts on the charge of drink-driving in England and Wales; of these, 48,883 were found guilty, a conviction rate of 97%. The conviction rate has remained constant over the last 5 years. Both the number of people proceeded against and those found guilty has fallen every year since 2007, and by a third [32%] over the period.

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