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Drug driving – A straight line for justice?

Written by: Alan Baker 20th November, 2014

Proposed legislation in 2015 should mean an end to the problem regularly faced by police forces when prosecuting drivers who may be under the influence of a drug.

Currently drivers face a tripod of evidence against them; alleged poor driving, the presence of a drug in their blood or urine and their perceived poor performance in a range of tests commonly know as Impairment Testing.

These latter tests are comprised of five elements; pupillary diameter, perception of time, walk and turn, one leg stand and finger to nose.

These tests are typically undertaken whilst the motorist is at the roadside and the decision about whether an individual is impaired is now usually made by a police officer rather than a doctor based on the individual’s performance in the tests.

Bericon Forensics has a long-standing view that the mandatory instructions given to individuals can be confusing and that the interpretation of any findings needs to be considered alongside their understanding of the tests together with an assessment of their general health and fitness.

To assess the efficiency of the tests, Bericon conducted a study into the performance of 20 individuals who reported to be free from drugs. The results showed that:

50% were not able to accurately estimate 30 seconds in time;

30% were not able to satisfactorily complete the walk and turn test;

30% were not able to correctly stand on one leg;

95% missed their nose at least once in the finger to nose test.

The failure of one or more of these tests could cause the officer to report that the individual was impaired.

Forensic experts at Bericon report that the findings support the view that the tests are a poor discriminator when assessing someone’s potential drug impairment and that matters are made complicated when the individual has a medical condition which may affect their movement and/or co-ordination.

However until scientific limits are in place for the concentration of selected drug types such as cannabis, heroin and cocaine in an individual’s blood, police forces will have to rely on tests which can be of limited and potentially distorted  value in some situations.

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