The results of standardized field sobriety tests (SFSTs) can be valuable evidence in impaired driving cases, but their persuasive force depends on whether jurors understand what SFSTs actually measure.
Defense attorneys often exploit the jury’s unfamiliarity with these tests by turning them into a series of confusing technical points rather than what they really are: practical demonstrations of the same mental and physical abilities required for safe driving. A successful trial presentation should clearly connect SFST performance to the core functions of driving, including reaction time, divided attention, visual tracking, balance, coordination, and judgment.
Before discussing the tests themselves, jurors should understand driving is not a simple physical act; it is a divided attention task requiring executive functioning. A driver must scan for hazards; track moving vehicles; remember traffic laws and instructions; divide attention among steering, speed, lane position, mirrors, signs, pedestrians, and other vehicles; and then make decisions and respond to changing conditions in real time. Research consistently shows alcohol and many other impairing substances affect reaction time, lane control, hazard perception, psychomotor coordination, attention, and judgment in ways that directly affect driving safety. This is why SFSTs matter: They test the same abilities impaired driving compromises.
The first step in explaining SFSTs is to focus the jury on what it means to drive safely. Driving is not just holding a steering wheel and pressing pedals; it requires continuous monitoring, rapid decision-making, and the ability to manage multiple demands at once. A driver at an intersection may need to remember a route, watch a pedestrian, track a changing traffic signal, judge oncoming speed, and decide whether to brake or proceed, all within seconds. When a person is impaired, that process breaks down in familiar ways: delayed braking, missed cues, drifting, swerving, poor judgment, and a failure to process more than one piece of information at a time.
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