Short answer: An Ontario DUI arrest typically follows this path: traffic stop or RIDE check → roadside screening (approved screening device, SFST, or oral-fluid drug test) → arrest if reasonable grounds → transport to the station → evidentiary breath, DRE, or blood testing → release on a promise to appear or bail . At every stage, Charter rights — especially right to counsel (s. 10(b)) and silence — apply, and procedural errors can become defence issues.
Being arrested for driving under the influence (DUI) in Ontario is a stressful and overwhelming experience. Whether the stop happens during a routine traffic check, after a collision, or because an officer suspects impairment, the process can feel intimidating — especially if you don't know your rights or what police are legally permitted to do.
A DUI charge can have life-changing consequences: licence suspension, fines, criminal records, increased insurance premiums, travel restrictions, and even jail in severe cases. Because the stakes are high, it's essential to understand how the DUI arrest process works, what police must follow, and where legal defences often arise.
This article provides a clear, Ontario-specific breakdown of the entire DUI arrest process — from the initial traffic stop to post-arrest release or detention — and explains where procedural and Charter issues commonly arise. (In Canada, "DUI" is popular U.S. terminology; the Criminal Code uses impaired operation and related Part VIII.1 offences — see the difference between DUI and DWI in Canada .)
Since the Criminal Code amendments in 2018, police in Ontario have the authority to stop any driver to conduct a sobriety check — even without observing erratic driving or signs of impairment. This is known as mandatory alcohol screening under s. 320.27(2) .
While mandatory screening increases enforcement, it does not eliminate the requirement that police follow constitutional protections. Any DUI arrest must still comply with:
If officers fail to comply with these rules, the defence may be able to challenge the admissibility of evidence or the validity of the arrest.
While random stops are allowed, most DUI arrests begin for predictable reasons:
In most cases, the officer begins by asking for your licence, insurance, and registration while observing your speech, coordination, and smell of alcohol or cannabis, as well as your behaviour.
You do not have to answer "Have you been drinking?" Anything you say can be used as evidence.
After the initial interaction, the officer may legally demand one of the following:
Police do not need suspicion of impairment to demand this test under mandatory alcohol screening. Refusing is a separate criminal offence — see what refusal or failure to provide a sample means in Canadian DUI law .
A result of:
Used when a breath device is unavailable or when drug impairment is suspected. This includes assessing:
Failing the SFST typically leads to arrest.
Used less frequently, but legal. Detects THC, cocaine, and methamphetamine.
Once an officer forms reasonable grounds to believe you are impaired or over 80, they must:
You may be handcuffed and placed in a cruiser. Your vehicle may be searched or towed.
You still have the right to remain silent — and should use it.
As Brian Brody, Criminal Defence Lawyer Partner at Mass Tsang , notes: "After the arrest, the biggest mistake people make is talking too much. Anything you say becomes evidence. Invoke your right to silence until you speak with a lawyer."
At the station, you will undergo formal testing that determines which offence you will be charged with. Police may require:
For suspected drug impairment, a certified Drug Recognition Expert (DRE) conducts a multi-step assessment examining:
Blood samples are used in:
You must be given:
If police fail any of these obligations, the defence may ask the court to exclude the results under s. 24(2) of the Charter .
Strict timing and procedural requirements protect drivers from unreliable or unconstitutional testing. Police must ensure:
Failure to comply allows defence lawyers to argue for the exclusion of breath or drug test results.
As Robbie Tsang, Criminal Defence Lawyer & Managing Partner , explains: "In many DUI cases, the legal defence doesn't focus on the alcohol level but on whether police followed the law. One procedural error can be enough to win a case."
After processing, you may be released on:
Police typically release individuals when they have a safe way home and no aggravating factors. You may be held for a bail hearing if:
Based on results and observations, Criminal Code charges may include:
Provincial consequences (immediate roadside suspension, vehicle impoundment, fines, ignition interlock) often apply in parallel. Penalty ranges and long-term consequences are charge-specific and change with aggravating factors — what matters first is whether the stop, screening, arrest, and station testing were done lawfully.
Experienced defence lawyers analyze every moment of the arrest to identify procedural errors or Charter violations. Common defence avenues include:
A single breach may be enough to exclude test results and undermine the Crown's case.
These are different legal events with different standards:
Confusing the two stages — or treating a roadside "fail" as automatic proof of over 80 — is a common misunderstanding and a frequent source of successful challenges.
During a DUI arrest in Canada, you have the following legal rights under the Charter of Rights and Freedoms:
Why this matters: If any of these rights are violated, your lawyer may argue to exclude the resulting evidence, which can lead to reduced or withdrawn charges.
If you've been arrested for DUI in Ontario, taking the proper steps immediately can protect your rights and improve your legal defence. Here's what to do:
Why it matters: These actions preserve key evidence and can help your defence lawyer challenge the legality of the stop, arrest, or testing procedures.
Mass Tsang LLP focuses on the arrest timeline itself — roadside demands, station testing, and Charter compliance — rather than generic penalty lists. That includes:
A DUI charge is serious, but a conviction is not inevitable. Many cases turn on whether police followed the law at the stop, arrest, or testing stage. Early advice helps preserve your options.
Yes. Mandatory alcohol screening laws allow police to stop any driver at any time without suspicion of impairment.
Refusing a lawful demand is a criminal offence under s. 320.15 and carries serious penalties — often comparable to or exceeding impaired-driving consequences.
Police must conduct evidentiary breath testing as soon as practicable after arrest. Unreasonable delays can support an application to exclude the results.
No. You have the right to remain silent, and anything you say can be used against you.
Yes. Cases are often resolved favourably when police fail to follow proper procedures or violate Charter rights — particularly where evidence is excluded.
Yes. DUI law is technical and time-sensitive. A lawyer can advise you immediately on bail, licence suspension, and how to challenge the arrest process.
Legal Content Disclaimer:
Legally Reviewed by
Jeff Mass
| Updated: August 26, 2026
