The Supreme Court of Canada has upheld the core of a tough legislative scheme to combat drunk drivers who fail breathalyzer tests.
However, the court struck down a provision requiring defendants to show precisely how a malfunctioning breathalyzer machine led to an inaccurate test result in their case.
In a 5-2 ruling, the majority said that defendants need only prove a machine either malfunctioned or was operated improperly by police. It is then up to the Crown to show that test results were accurate in spite of the error.
The Supreme Court used its powers to excise the unconstitutional provision from the Criminal Code.
While Friday's decision leaves defence lawyers a toehold to battle against breathalyzer evidence, the judgment was largely a triumph for federal attempts to beef up impaired-driving laws.
In particular, the court upheld a key provision designed to foil the so-called "two-beer defence" – a highly effective defence argument that had resulted in numerous acquittals.
Under the defence, defendants typically testified that they had only consumed a couple of drinks before getting behind the wheel of a vehicle. The defence would then produce a toxicology expert to testify that the defendants would have been unlikely to register such a high breath-test reading unless the machine had malfunctioned or been operated improperly.
Alternatively, defendants sometimes argued that they consumed their last drink not long before the breath test was administered, which could result in more alcohol on their breath than was actually in their blood.
The defence was frequently sufficient to provide trial judges with a reasonable doubt that the accused was guilty.
Toronto defence counsel Jonathan Rosenthal said the court ruling largely affirmed "the validity of the government's attempting to deal with the serious social problems of drinking and driving, as well as their responsibility to improve enforcement and the governments concern with the 'two-beer defence.'"
However, Mr. Rosenthal said the judges criticized the law for wrongly treating breathalyzer tests as if they are infallible.
"The court has properly allowed that in cases in which trial judges are left with a reasonable doubt about the operation or malfunction of the machine, the prosecution may fail," he said.
Mr. Rosenthal predicted that the decision will lead to police and prosecutors having to routinely produce records disclosing breathalyzer maintenance records and the credentials of their operators.
Impaired driving charges make up a substantial proportion of criminal court cases, and fighting them is a staple of many defence lawyers' practices.
For decades, legislators have played a cat-and-mouse game with the defence over the reliability of breathalyzer results. Friday's ruling concluded a three-year challenge launched to restore the legitimacy of the two-beer defence.
The Criminal Code changes, part of the federal government's Tackling Violent Crime Act, were an attempt to reduce the effectiveness of defence attacks on their integrity.
Bolstered by a legal intervention by the Criminal Lawyers Association, lawyers for the defendants argued that the law set an impossible standard of proof for defendants. They maintained that it virtually guaranteed a conviction, frequently leading to the loss of one's driver's licence.
In a second case decided Friday, the Court ruled that the 2009 impaired driving provisions do not apply retroactively to those who had already been charged with impaired driving at the time the new law came into effect.