Standardized Field Sobriety Test (SFST)
A Standardized Field Sobriety Test, or SFST, is a structured three-part assessment performed at roadside to detect impairment by alcohol or drugs. SFSTs are authorized by section 320.27(1) of the Criminal Code when an officer has reasonable suspicion that the driver has alcohol or a drug in their body. The SFST is more elaborate than an ASD demand and is typically used where drug impairment is suspected or where breath-alcohol screening alone may not capture the impairment.
Mass Tsang's DUI lawyers examine the conduct of every SFST in detail. For more on roadside screening, see our blog post on how police use roadside screening tools in Ontario.
The three components
The standard SFST has three components: (1) Horizontal Gaze Nystagmus (HGN) — the officer observes the driver's eyes as they follow a moving stimulus, looking for involuntary eye movements indicative of impairment; (2) Walk-and-Turn — the driver walks heel-to-toe along a straight line, turns, and walks back, while the officer assesses balance, instruction-following, and motor function; (3) One-Leg Stand — the driver stands on one leg with arms at their sides while counting aloud for approximately 30 seconds, while the officer assesses balance and coordination.
When SFSTs are demanded
Section 320.27(1) authorizes an SFST demand where the officer has reasonable suspicion that the driver has alcohol or a drug in their body and has operated a conveyance within the preceding three hours. Failure to comply with an SFST demand is itself a criminal offence under section 320.15. The demand triggers Charter section 10 rights — implementation of the right to counsel must be considered, though there is no automatic right to counsel before performing the SFST itself.
How SFST results are used
Failed SFST performance can provide reasonable grounds to believe the driver is impaired, supporting a further demand for evidentiary breath testing (under section 320.28) or a Drug Recognition Evaluation. The SFST itself does not prove impairment beyond a reasonable doubt — it is an investigative screening tool. The trained officer's observations and conclusions are admissible at trial, but they are not conclusive.
Defence challenges
Defence challenges to SFST evidence commonly include: improper administration (failure to give standard instructions, deviations from training protocols); officer qualifications and training currency; environmental conditions (uneven ground, poor lighting, weather, traffic, footwear); medical conditions affecting balance or eye movement (inner-ear conditions, leg injuries, anxiety); language barriers affecting instruction comprehension; the inherent limitations of the tests in clinical research literature; Charter issues with the underlying detention, demand, or right-to-counsel implementation; and challenges to whether the threshold of reasonable suspicion existed for the demand.
Related glossary terms
