Drug driving and impairment testing

Categories: Forensic Casework experiences, New Zealand specific, News, Opinion, Sciblogs

Drug driving is illegal in many countries including New Zealand and the UK.  New Zealand has recently (June 2009) changed the law in order to increase the rate of successful prosecutions .  These changes, which come into force in December 2009, include giving the Police the power to conduct roadside impairment tests.  Such tests were introduced in England & Wales in 2004.  As a forensic scientist working largely for the Defence at that time, these changes resulted in a) more casework coming through our door; and b) more successful prosecutions.  As long as the Police covered off all relevant points it was very unlikely a case would fail.

My involvement was to assess whether or not the various points had been covered.  These included:

  • a witness (including a Police Officer) who could talk about the manner of driving of the Driver at the time in question;
  • the results of roadside impairment tests undertaken by the Driver under the supervision and direction of a specially-trained Police Officer.  If the Officer deemed that the Driver had performed poorly then they had grounds for arrest and transfer of the Driver to the Police Station.
  • once at the Police Station, a medic is required to examine the Driver.  This allows the medic to rule out any medical cause for any impairment observed by the Police Officer at the scene – the Driver usually has to re-do some or all of the impairment tests.  If the medic formed the opinion that the Driver was impaired through the use of drugs, a blood sample could be taken.  Without this opinion the taking of a blood sample was not allowed.
  • the blood sample would be analysed to detect the presence of a range of commonly-encountered drugs (prescription and illegal) that can adversely affect driving performance. Some drug or metabolite would need to be identified in order to confirm that the Driver may have been under the influence of drugs at the time in question.

All of the above had to be in place for a successful prosecution.  The law change in New Zealand seems to be along similar lines but only time will tell how well the Police and the legal system deal with the changes.

Despite the law changes in England & Wales being successful (in my experience at least), the UK government has announced a new ad campaign warning of the dangers of drug driving. The adverts will advise drivers that the Police can spot the signs of whether someone may be under the influence of drugs using the tag line  “Your eyes will give you away.” It’s true of course.  Drugs affect difference people in different ways but can be generalised.  For instance, depressants such as cannabis impair a driver’s perception of distance, time and speed as well as restrict the ability to do two things at once (such as look for traffic and change gear).  Cocaine is a stimulant and can cause people to take risks such as driving at high speed in a dangerous manner.

People cannot control how drugs affect them, particularly when combined, such as cocaine and alcohol.  Time will tell whether the law change in New Zealand helps combat the problem.

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Forensic Scientist