Australia's drug driving laws criminalise individuals who represent no risk to other drivers, making a mockery of the law as a tool for reasonably managing risk in a community, writes Greg Barns.

Every Australian jurisdiction has, over the past decade, passed laws that make it an offence to have any trace of an illicit drug in your blood when you are driving. It does not matter that your driving is exemplary or that the trace of drugs in your blood is from a couple of puffs of a cannabis joint a few days earlier.

In most states and territories the court will have no choice but to disqualify or cancel a first time offender's drivers licence for a period of between a minimum of three months and maximum of six to nine months.

Drug driving laws are grossly unfair. They are not based on data or scientific knowledge.

These laws are under pressure in the United States with the advent of medical cannabis and an acknowledgement by one superior court last month that it is patently unjust to penalise a person who does not threaten other road users in any way.

The inherent unfairness of drug driving laws can be illustrated by comparing them to drink driving laws.

The link between alcohol and road deaths and injuries is well known, as Assistant Professor Andrea Roth wrote about in the California Law Review last year.

In the article, Assistant Professor Roth described the work by epidemiologists - who in the 1940s, 1950s and early 1960, along with law enforcement researchers and medical scientists undertook exhaustive studies and tests - to prove a link between the level of alcohol in a person's blood and how it impairs their capacity to drive a motor vehicle safely.

We base our drink driving laws on this demonstrably correct data and accordingly allow for some alcohol in the bloodstream for full drivers licence holders, so long as it is below a blood alcohol content of 0.05 per cent.

But not so with other drugs such as cannabis. Here we take the prohibitionist stance and apply it to driving without bothering to undertake the rigorous analysis that accompanied and underpinned drink driving law development.

This is admitted by researchers in the field. Roth cites a 2007 paper published in Addiction by Franjo Grotenhermen and colleagues who observed:

"A zero tolerance approach to drugs while driving "avoid[s] the need for a reliable science-based correlation between drug concentration and level of impairment".

As Professor Roth observes, it is a case of legislators being lazy and simply saying "a prohibitionist stance would have to do."

Dr Alex Wodak, now Chair of the Australian Drug Law Reform Foundation and formerly head of drug and alcohol services at St Vincent's Hospital in Sydney, notes that:

"One of the problems with 'zero tolerance' drug driving laws is that they punish some drivers who are not impaired as a way of deterring other drivers who might be impaired or might become impaired from driving. This is what we call 'vicarious punishment' and it offends basic notions of fairness."

Or, as Professor Roth puts it, "punishment without purpose is immoral."

In short, Australia's drug driving laws have no evidential basis but can have severe impacts on the rights of individuals and their families, given that the loss of a drivers licence can mean losing your job.

The US is now grappling with the consequences of the immorality and injustice of zero tolerance drug driving laws in the context of the legalisation of cannabis for both medical and recreational purposes.

You cannot allow people to use cannabis legitimately but then criminalise them if they drive.

Some states, such as Washington and Montana, have adopted limits for cannabis presence in the bloodstream analogous to 0.05 per cent laws.

But to quote Professor Roth again, even these more liberal laws are not legitimate because "there is no demonstrated linear or predictable relationship between THC blood limits and an increased crash risk."

The Arizona Supreme Court weighed into the issue last December in a landmark ruling when it identified the flaw in zero tolerance drug driving laws.

It noted that a driver cannot be considered to be " 'under the influence' based solely on concentrations of marijuana or its metabolites that are insufficient to cause impairment."

In other words, it is only legitimate as a matter of justice and sound public policy to prosecute individuals about whom it can be shown that the concentration of the drug in their blood steam meant that they presented a risk to other road users.

Australian courts are, literally on a daily basis, dealing with drug driving cases and criminalising individuals who represent no risk to other road users. This is making a mockery of the law as a tool for ensuring that risk in a community is managed reasonably.

Drug driving laws must be reformed and this can only be done by governments spending money on pursuing rigorous analysis of the impact of drugs on driving.

The only offence which ought to be on the statute books is one based, as is the case in respect of drink driving laws, where there is a strong research consensus on causation between the substance in a person's blood stream and impairment.

Greg Barns is a barrister and a spokesman for the Australian Lawyers Alliance.