The process that leads up to a prosecution on DUI charges typically often begins with a police officer’s reasonable suspicion that a driver has alcohol in their body before they make an Approved Screening Device (ASD) roadside test demand (as defined in the Criminal Code, s.254(2)). However, when an officer stops a motor vehicle and during his investigation forms reasonable and probable grounds that a person’s ability to operate a motor vehicle is impaired by alcohol, they are entitled to arrest a driver under s. 254(3) of the Criminal Code without giving them an ASD roadside test.

The conclusion of a DUI prosecution involves the ‘standard’ for any conviction, which is proof beyond a reasonable doubt that the driver’s ability was impaired by alcohol. In a 2016 trial, R. v. Constable, a man was acquitted on both charges, Impaired Driving and Over 80, because neither charge was proven beyond a reasonable doubt. 


The circumstances leading to the man’s arrest on DUI charges began when a McDonald’s drive-through employee believed that she smelled alcohol in the man’s vehicle and thought that his coordination was ‘off’. Based on these perceptions, the employee recorded the man’s licence plate and called 911. After hearing the radio call reporting the alleged impaired driving incident, a York police officer was en route to the accused person’s home address when he observed the man’s car weaving on Civic Center Road. The driver’s actions were also captured on the police cruiser’s dash camera. Although the officer activated his lights, the driver of the car did not pull over and the officer followed him until the man pulled into his driveway. 

Analysis and Findings

The officer testified that the driver appeared to be walking unsteadily when he got out of his car and also, that his eyes appeared glassy and his speech was slightly slurred. The officer noticed several empty beer cans in the car, as well. As a result of these observations, the officer asked the man to sit in the police cruiser whereupon the man was placed under arrest for impaired operation of a motor vehicle; he was read his right to counsel and was given an appropriate ASD breath demand.

In addition to claims that the man was driving erratically, unsteady on his feet and speaking with slurred speech, the officer testified that he smelled alcohol on the man’s breath once he was in the cruiser. At the trial, the officer admitted that he had a reasonable suspicion, enough to demand a roadside test, before placing the defendant in his cruiser, but it was also his intention to monitor for the smell of alcohol once the man was in the police car, to determine if there were reasonable grounds for an arrest.

The prosecution’s evidence included the breath technician’s alcohol influence report as well as an opinion letter completed by an expert toxicologist. The toxicologist concluded that the defendant’s blood alcohol concentration (BAC) was between 115 and 170 mg at the time he was stopped by the police. 

Key Arguments

The key arguments and issues raised by the defence were as follows.

  1. Was there a breach of the defendant’s Charter rights under section 8, and should the breath tests, therefore, be excluded as evidence under s. 24(2)?
  2. Was the Crown successful in proving an absence of bolus drinking (defined as significant or large quantities of alcohol consumption within 15 minutes of the police stopping the accused’s vehicle which would therefore not be absorbed in the accused’s bloodstream at the time of the stop)?
  3. Has the Crown proven beyond reasonable doubt that the defendant’s ability to drive was impaired?

With respect to the allegation that the defendant’s Charter rights were violated, the judge noted that “reasonable and probable grounds has both a subjective and objective component”. The subjective aspect is the officer’s genuine belief that the subject committed a DUI offence and the objective component requires a reasonable person to come to the same conclusions as the officer when put in the same position. Based on the totality of the circumstances, which included the arresting officer’s experience and training as well witness/hearsay evidence, the judge concluded that the defendant’s arrest was made on reasonable and probable grounds. In this case, the judge concluded that a reasonable person would have reached the same conclusion as the officer if they had received information about a possible impaired driver and if they also observed somewhat erratic driving, a failure to stop when the cruiser’s roof lights were engaged and other (later) indicators of likely impairment.

Defence counsel also challenged the toxicologist’s assumption that the defendant had not consumed ‘large quantities of alcohol’ within 15 minutes of the police stopping his vehicle and that there was no bolus drinking. The defendant advised the officer at the time of the stop that he was not drinking when he was detained on suspicion of the DUI offences; however, the arresting officer admitted that the open beer cans in the vehicle suggested to him that the defendant may in fact have been drinking up to the point of his arrest. The judge placed no weight on the defendant’s initial denial of drinking while driving but rather, concluded that evidence, such as open beer cans and a strong smell of alcohol, suggested that there was a consumption of alcohol prior to being stopped by the officer. On the weight of this evidence, the judge could not accept the toxicologist’s conclusions about the defendant’s BAC at the time of the accident and thus, he acquitted the defendant on the Over 80 charge.

With respect to the impaired driving charge, although the officer observed the smell of alcohol, an unsteady gait and slurred speech on the defendant, the evidence of bad or erratic driving was actually quite insubstantial, particularly as viewed from the dash camera recording. The most significant concern was when the defendant’s car came into contact with the shoulder of the road, which could be explained if he was eating while driving. As he had just purchased a meal at McDonald’s and there were food wrappers found in his vehicle, eating while driving was a reasonable explanation for his driving behaviour. 


The court cited the Ontario Court of Appeal ruling in R. v. Stellato where it was stated, “…before convicting an accused of impaired driving, the trial judge must be satisfied that the accused’s ability to operate a motor vehicle was impaired by alcohol or a drug. If the evidence of impairment is so frail as to leave the trial judge with a reasonable doubt as to impairment, the accused must be acquitted.” In R v. Constable, the judge concluded that the crown had not proven the impaired driving charge beyond a reasonable doubt and accordingly, the defendant was acquitted on the charge of impaired driving.

Even when there are reasonable grounds to make an arrest on the charges of impaired driving and over 80, these initial grounds do not necessarily prove, beyond a reasonable doubt, that the accused person is actually guilty of these offences. Accordingly, in R. v Constable, the prosecution’s failure to prove that the defendant committed these DUI offences beyond a reasonable doubt was the reason for a dismissal on both charges.

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