SFST Breakdown, What Attorneys Should Look For in Roadside Tests
Overview
Standardized Field Sobriety Tests are one of the most commonly used components in DUI investigations, yet they are also one of the most frequently misunderstood. Attorneys know that SFSTs can make or break probable cause, but only when they are evaluated through a precise, technical lens.
Zach Marshall, a DUI and collision evaluation expert based in Arlington, WA, provides structured SFST analysis to help defense attorneys understand whether test performance and officer scoring align with NHTSA standards.
As the founder of Legal Limit Consulting, LLC, Zach focuses on the reliability, consistency, and procedural accuracy of SFSTs. His evaluations provide attorneys with clear insight into whether the tests were administered correctly, whether clues were interpreted properly, and whether the results can be defended scientifically.
Understanding What SFSTs Are, And What They Are Not
SFSTs are not a measure of guilt or innocence. They are standardized roadside assessments designed to help officers make decisions about impairment. For those tests to be reliable, they must be administered and interpreted exactly as NHTSA requires.
Attorneys benefit from knowing:
SFSTs are vulnerable to environmental and subject related factors
Minor deviations in instruction or demonstration can affect performance
Scoring must follow strict guidelines
Camera to report comparison is essential
Proper articulation is required for each observed clue
A careful review often reveals inconsistencies that may not be visible at first glance.
Horizontal Gaze Nystagmus (HGN)
HGN requires the highest degree of technical accuracy. Zachary examines:
Stimulus distance and angle
Pace of each pass
Smooth pursuit evaluation
Maximum deviation hold times
Onset of nystagmus accuracy
Proper check for resting nystagmus
Equal tracking confirmation
Camera angle versus officer observation
Because HGN clues are dependent on exact timing and movement, even small errors can significantly change the reliability of the test.
Walk and Turn
The Walk and Turn is often scored incorrectly or demonstrated inconsistently. Zachary reviews:
Instruction stance
Clarity and accuracy of the verbal instructions
Quality of the officer demonstration
Line surface and environmental conditions
Clue interpretation
Missed or incorrectly attributed clues
Impact of footwear, roadway slope, or lighting
Whether the instructions were understood
Attorneys often find that the Walk and Turn test evaluation contains procedural weaknesses that directly affect probable cause.
One Leg Stand
This test requires balance, concentration, and environmental fairness. Zachary evaluates:
Instruction clarity
Timing accuracy
Officer demonstration quality
Subject footwear and surface
Clue scoring
Subject specific factors, including injuries or stability issues
Camera evidence compared to written documentation
Mis-scored One Leg Stand tests are common, especially in cases involving fatigue, cold conditions, or uneven surfaces.
Environmental and Human Factors
SFSTs are sensitive to conditions that have nothing to do with alcohol or drug impairment. Zachary identifies factors such as:
Weather
Roadway slope
Footwear
Lighting
Traffic distraction
Subject anxiety or fatigue
Medical conditions
Officer positioning
When these conditions are present, they can reduce reliability and create challengeable inconsistencies.
Video Review and Report Comparison
Every SFST should be compared to bodycam and dashcam evidence. Zachary analyzes:
Whether camera evidence supports the written clues
Timing discrepancies
Demonstration issues
Articulation gaps
Moments that contradict impairment claims
These comparisons frequently become key leverage points for negotiations or suppression arguments.
Why Attorneys Rely On This Analysis
Attorneys hire Zach because his SFST evaluations reveal the technical issues that impact reliability. These issues often shape:
Probable cause determination
Suppression arguments
Trial strategy
Cross examination of the investigating officer
Negotiation leverage
A structured review of SFSTs allows attorneys to clearly identify what the tests actually show, not what they are assumed to show.
Contact
To request an SFST focused review or DUI case evaluation, contact:
Zachary Marshall
Founder and Lead Consultant, Legal Limit Consulting, LLC
Arlington, Washington
Phone: (425) 224 5149
Email: Z.Marshall@LegalLimitConsulting.com
Website: www.LegalLimitConsulting.com
Download Attorney Facing SFST Reliability Checklist
