If you’ve been stopped for suspected impaired driving in Canada, you’ll likely encounter two different types of breath testing: the roadside screening device and the station breathalyzer. Understanding the critical differences between these tests, and their different legal implications, is essential for anyone facing DUI charges.
The Approved Screening Device (ASD)
The roadside breath test uses a portable Approved Screening Device—commonly a Dräger Alcotest 6810 or Alco-Sensor IV.
Purpose: ASDs provide police with:
- Reasonable grounds to make further demands
- Confirmation of alcohol presence
- General indication of intoxication level
How it works:
- You blow into a small handheld device
- Results appear within seconds
- Shows “fail,” “warn,” or “pass” (or a range like 50-100mg)
Legal authority: Under Section 320.27 of the Criminal Code, police can demand a roadside breath sample if they:
- Have reasonable suspicion you have alcohol in your body (for traditional ASD demands)
- Have lawfully stopped you for any reason (for Mandatory Alcohol Screening)
You must comply immediately. Refusal carries the same criminal penalties as impaired driving itself—minimum $2,000 fine for first offence.
The Approved Instrument (Station Breathalyzer)
If you fail or refuse the roadside test, police demand you accompany them to the station for testing on an approved instrument—typically an Intoxilyzer 8000C or Datamaster C.
Purpose: These sophisticated machines provide:
- Precise BAC measurements
- Admissible evidence for criminal prosecution
- Results that can be used to prove charges in court
How it works:
- Two breath samples taken 15 minutes apart
- Deep lung air analyzed using infrared spectroscopy
- Printout showing exact BAC measurements
- Samples must be within 20mg of each other
Legal authority: Section 320.28 allows police to demand breath samples if they have reasonable grounds to believe:
- You committed an impaired driving offence within the preceding three hours
- The demand is made “as soon as practicable”
Key Differences Between Roadside and Station Tests
1. Legal Admissibility
Roadside ASD: Results are generally NOT admissible to prove your actual BAC in court. They’re used only to establish grounds for arrest and further testing.
Station breathalyzer: Results ARE admissible as evidence of your BAC and can be used to prove you were over 0.08.
This distinction is crucial. Even if you “failed” the roadside test, the Crown typically cannot use that result to convict you—they need station results.
2. Accuracy and Reliability
Alexander Karapancev a seasoned Toronto DUI Lawyer explains, “Roadside devices are far less accurate than station instruments. They’re more susceptible to environmental factors, mouth alcohol contamination, and give only approximations. Station instruments are calibrated to forensic standards and designed for evidentiary purposes.”
Roadside devices:
- Margin of error: ±20-30mg
- Susceptible to temperature, humidity
- More false positives from mouth alcohol
- Less stringent calibration
Station instruments:
- Margin of error: ±10mg
- Climate-controlled testing environment
- Sophisticated mouth alcohol detection
- Rigorous calibration requirements
3. Right to Counsel
Roadside test: You do NOT have the right to speak with a lawyer before providing a roadside breath sample. You must comply immediately with the demand.
Station test: You DO have the right to speak with a lawyer before providing breath samples at the station. Police must:
- Inform you of this right
- Provide a reasonable opportunity to exercise it
- Not continue testing until you’ve had that opportunity
This Charter right is critical and frequently violated by police.
4. Procedural Requirements
Roadside:
- Minimal procedures
- Immediate demand and testing
- No observation period required
- Officer simply hands you the device
Station:
- Strict procedural requirements
- 15-minute observation period (ensuring no mouth alcohol)
- Qualified technician must administer
- Specific protocols for sample collection
- Detailed documentation required
Violations of station procedures can result in exclusion of evidence.
Why These Differences Matter for Your Defence
Challenge Station Test, Not Roadside
Defence lawyers focus on challenging station breath tests because:
- Those results are what the Crown uses for conviction
- Station tests have more procedural requirements (more opportunities for police error)
- Charter rights apply at the station (not roadside)
Even if you “failed” roadside, you might still beat the charges based on problems with station testing.
Roadside Results Can Help the Defence
Sometimes roadside results actually help:
Example: Roadside shows “warn” (under 100mg), but station shows 110mg. This suggests rising BAC—supporting a defence that you were under 0.08 while driving but over by the time station testing occurred.
Different Legal Tests Apply
For roadside demands, police need only:
- Reasonable suspicion of alcohol (very low threshold)
- OR any lawful stop (for mandatory alcohol screening)
For station demands, police need:
- Reasonable grounds to believe you committed an offence (higher threshold)
If police lacked proper grounds for the station demand, results may be excluded even if the roadside test was lawful.
Common Mistakes People Make
Refusing roadside but not station: Some people refuse the roadside test hoping to avoid charges. This results in:
- Immediate criminal charges for refusal
- Station testing anyway
- No strategic advantage
Assuming roadside results prove the case: Many people believe failing roadside means automatic conviction. The station test is what matters.
Not exercising right to counsel at station: People rush through station testing without speaking to a lawyer, missing the opportunity to obtain legal advice about their rights.
Strategic Implications
Understanding the difference between these tests allows for strategic defence:
Timeline analysis: Comparing roadside and station results reveals BAC trends (rising vs. falling).
Procedural challenges: Station testing has more requirements that police can violate.
Charter arguments: Rights violations occur at the station, not roadside.
Technical challenges: Station instruments have more sophisticated technology that can be challenged by experts.
The Bottom Line
Roadside and station breath tests are fundamentally different tools serving different purposes. Roadside tests are preliminary screening tools that aren’t admissible to prove your BAC. Station tests are forensic instruments providing evidence for prosecution.
This distinction matters enormously for your defence. Many people who failed roadside tests successfully beat DUI charges based on problems with station testing procedures, Charter violations, or technical reliability issues.
If you’re facing DUI charges, don’t assume failing the roadside test means you’re automatically guilty. The station test is what counts, and those results can be challenged on numerous grounds that experienced counsel will identify.
Understanding these technical distinctions is essential for mounting an effective defence to impaired driving charges.