How Ontario Actually Enforces Impaired Driving Laws at the Roadside
Last reviewed: 2026 · Driviology Road Safety Education Team
Quick Answer
Ontario's impaired driving laws are enforced at the roadside through approved screening devices, officer observation, and discretion, which together determine whether a driver proceeds to further testing.
Beyond the penalty structure and legal categories, it helps to understand how impaired driving laws are actually enforced in the moment at the roadside.
Roadside Screening
An approved screening device measures blood alcohol concentration at the roadside, feeding directly into the thresholds described in our guide to blood alcohol concentration.
Officer Observation and Discretion
Beyond any device reading, an officer’s direct observations - slurred speech, odour, unsteady movement - factor into the decision on how to proceed, alongside the broader legal framework covered in our guide to Ontario’s DUI laws.
What Happens After a Failed Screening
A failed roadside screening typically leads to further testing and an immediate licence suspension, connecting directly to the broader picture described in our guide to impaired driving in Ontario.