If a police officer pulls you over on suspicion of drunk driving in Missouri, one of the first things they may ask you to do is step out of the car and perform field sobriety tests. These roadside tests are used by law enforcement officers to assess whether a driver may be impaired. Understanding what these tests involve, whether you're required to take them, and how they're used in court can make a critical difference in your case.
What Are Field Sobriety Tests?
Field sobriety tests are a series of physical and cognitive exercises that law enforcement officers use during a traffic stop to evaluate signs of impairment. Unlike a breath test or blood test, these tests rely entirely on the officer's observations and judgment. That means there's significant room for error — and for challenge in court.
The National Highway Traffic Safety Administration (NHTSA) has established standardized field sobriety testing procedures, but not all officers follow them exactly. Any deviation from the approved procedures can affect the reliability of the results.
The Three Standardized Field Sobriety Tests in Missouri
Missouri law enforcement officers are trained to use three tests approved by NHTSA for standardized field sobriety testing:
Horizontal Gaze Nystagmus Test
The horizontal gaze nystagmus (HGN) test involves following a moving object — typically a pen or fingertip — with your eyes. Officers look for involuntary jerking of the eyes called nystagmus, which can be more pronounced when a person is impaired by alcohol. The officer moves the object horizontally while observing each eye for up to six clues. However, nystagmus can also be caused by medical conditions, certain medications, or even fatigue. Without a controlled environment, the HGN eye test result is far from definitive.
Walk and Turn Test
In the walk and turn test, the suspect is asked to take exactly nine steps heel to toe along a straight line, turn, and return. Officers watch for specific clues — starting before instructions are finished, stepping off the straight line, using arms for balance, or failing to follow instructions to count steps aloud. This divided attention test is designed to stress both your physical coordination and your ability to follow instructions simultaneously. Officers determine impairment based on how many clues appear during the test.
One Leg Stand Test
The one leg stand test requires you to stand on one leg with your foot about six inches off the ground while counting aloud. Officers look for swaying, using arms to balance, hopping, or putting your foot down. People with inner ear problems, injuries, or who are simply nervous can fail this test without any alcohol in their system.
Non-Standardized Field Sobriety Tests
In addition to the three NHTSA-approved tests, officers sometimes use non-standardized tests — such as the finger to nose test, reciting the alphabet backwards, or counting down from a number. These non-standardized tests have no scientific validation and are even more susceptible to challenge. A criminal defense attorney can argue that these tests are unreliable and should carry little weight with a jury.
What Officers Are Looking For During a DWI Stop
When an arresting officer asks a suspect to exit the vehicle and perform field sobriety tests, they are trained to conduct each test in the same manner every time. The officer follows instructions from NHTSA certification and documents signs of intoxication — not just whether the driver passes or fails each test, but exactly how many clues were observed.
A driver's level of impairment is evaluated across all three tests together. Courts have found, however, that the inherently flawed nature of roadside tests — conducted under stress, on uneven surfaces, with vehicles passing nearby — means the results must be carefully scrutinized. Missouri DWI and DUI case law recognizes that field observations carry significant weight, but defense attorneys routinely challenge them on procedural and factual grounds.
Charged with DWI after a field sobriety test?
The tests may have been administered incorrectly, or your performance may have had nothing to do with alcohol. Bur Oak Legal represents people charged with DWI across central Missouri. Free consultation — no fee unless we win.
Get a free consultation →Can You Refuse a Field Sobriety Test in Missouri?
Yes. Unlike a chemical test (breath test or blood test), field sobriety tests in Missouri are not covered by implied consent law. Missouri's DWI statutes under Chapter 577 RSMo require drivers to submit to chemical testing when lawfully arrested for DWI, but they do not require participation in roadside sobriety tests.
That said, refusing field sobriety tests doesn't mean you'll avoid a DWI arrest. Officers can still arrest you based on other observations — slurred speech, the smell of alcohol, erratic driving. Refusing the tests simply means there's less evidence for the prosecution to use against you at trial.
If you were arrested for DWI after refusing or performing field sobriety tests, contact a criminal defense attorney right away. The sooner you have representation, the better your options.
How Field Sobriety Test Results Are Used in Court
In a Missouri DWI case, the prosecutor will often use field sobriety test results as part of the evidence against you — especially if your chemical test result was close to the legal limit or if no chemical test was taken. Officers typically document their observations in a police report and testify at trial about what they observed during the roadside tests.
Field sobriety test results are not as objective as they may sound. They depend heavily on the officer's training, the conditions on the roadside, and how instructions were given. Defense attorneys look closely at the officer's certification records, the lighting and terrain at the stop, and whether the tests were administered according to NHTSA guidelines. Understanding the Missouri criminal court process from the outset gives you a meaningful advantage.
Challenging Field Sobriety Tests in a Missouri DWI Case
There are several well-established grounds for challenging field sobriety test results in a Missouri DWI defense:
Improper administration: If the officer didn't follow standardized field sobriety testing procedures — wrong number of steps, improper instructions, failing to ask about medical conditions — the results may be suppressed or discredited.
Medical or physical conditions: Knee injuries, inner ear problems, neurological conditions, and even poor footwear can all affect performance on these tests. An attorney can present evidence that your performance had nothing to do with alcohol impairment.
Environmental factors: Uneven pavement, poor lighting, heavy traffic noise, and bad weather conditions on Missouri roads can all compromise test performance.
Officer credibility: In some cases, the officer's training records, past conduct, or inconsistencies in the police report can be used to challenge their testimony.
At Bur Oak Legal, Chris Miller reviews every aspect of the traffic stop — from the reason for the stop to how each roadside test was conducted — to identify weaknesses in the prosecution's case. There are no handoffs to associates or paralegals — your case stays with Chris from the first call to the final outcome.
If you or someone you know is facing DWI charges in central Missouri, also consider how this charge intersects with your other legal rights. Our criminal defense and personal injury practice areas may be relevant depending on your situation.