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Would you pass a drug-driving test?

If you haven't taken drugs, passing a drug-driving test should be easy, right? Not necessarily, according to motoring lawyer Jeanette Miller.

Assorted drugs

On 2nd March 2015, legislation changed to make it easier for police to apprehend and convict drivers who drive under the influence of drugs.

Police can stop and search motorists at any time, so long as they are acting "in the execution of their duty".

Previously, tests involved not only proving that a driver was under the influence of drugs, but also that their driving was impaired, which was incredibly complicated.

Legislation said that:

"A person who, when driving or attempting to drive a [mechanically propelled vehicle] on a road or other public place, is unfit to drive through drink or drugs is guilty of an offence."

But since the law changed, if police stop you and suspect you're on drugs, they can test you at the roadside using either a drug screening device, or a "field impairment" test.

If you have a certain level of drugs in your system – and this includes legal drugs – there will be no need to prove that you're impaired in any way.

The drug-driving limits

It's important to note that the limits are not set at zero, as drugs taken for medical conditions can be absorbed in the body to produce trace effects.

Different drugs are broken down at different speeds, which is reflected in the varying limits, expressed in microgrammes per litre of blood (µg/L). 

16 drug types have so far been allocated limits for a drug-driving offence:

Illegal drugs

  • Benzoylecgonine, 50 µg/L (Contained in cocaine)
  • Cocaine, 10 µg/L
  • Delta–9–Tetrahydrocannabinol (cannabis and cannabinol), 2 µg/L
  • Ketamine, 20 µg/L
  • Lysergic Acid Diethylamide (LSD), 1 µg/L
  • Methylamphetamine - 10 µg/L
  • Methylenedioxymethaphetamine (MDMA – ecstasy), 10 µg/L
  • 6-Monoacetylmorphine (6-MAM – heroin and morphine), 5 µg/L

General prescription drugs

  • Clonazepam, 50 µg/L
  • Diazepam, 550 µg/L
  • Flunitrazepam, 300 µg/L
  • Lorazepam, 100 µg/L
  • Methadone, 500 µg/L
  • Morphine, 80 µg/L
  • Oxazepam, 300 µg/L
  • Temazepam, 1000 µg/L

Field impairment tests

Policeman giving roadside sobriety test

In place of a drug screening device, police may also try to determine if drugs have impaired your ability to drive with a field impairment test.

The tests are split into five sections:

1. Pupillary test

Watch out if you wear contact lenses or suffer with watery eyes as this could be enough for the police to decide you're impaired when they check the size of your pupils.

They will test your pupils’ size, condition and reaction to light, which are often affected by drugs.

2. Romberg test

The police ask you to stand and balance with your eyes closed and head tilted back. You then have to count to 30 in your head.

They will be watching how accurately you count 30 seconds, which can be impaired by drugs, as well as how you balance.

3. Walk and run test

You might be asked to walk heel-to-toe along a straight line while counting the steps out loud and looking at your feet.

They'll be watching out for you missing a count, a step, tripping, or stepping off the line.

4. One leg stand test

The next test involves you being asked to stand on one leg for as long as the officer decides, while counting out aloud.

Police will watch out for swaying, loss of balance or not following instructions.

5. Finger nose test

You'll be asked to tilt your head back slightly and close your eyes. When told which hand to use, you must touch the tip of your nose with your finger, as a test of depth perception.

Failing the test

Unlike a urine or blood test, the field impairment tests cannot exactly be passed or failed, but are rather used by police officers as a gauge.

They'll watch you, and decide based on your performance whether you should be arrested for drug or drink-driving, and taken for a full drug test.

Penalties for drug-driving

Handcuffs, drugs and fingerprints

If you're convicted of drug-driving you can expect to get:

  • a minimum 1 year driving ban
  • an unlimited fine
  • up to six months in prison
  • a criminal record

Your licence will show you’ve been convicted for drug-driving, which will last for 11 years.

You can also expect to see your car insurance costs rise significantly, and may have trouble travelling to certain countries like the USA.

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Jeanette Miller

Jeanette Miller

Lawyer and legal blogger Jeanette Miller is managing director of motoring law specialists Geoffrey Miller Solicitors.

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