Field Tests

Pennsylvania Field Tests

Field tests or field sobriety tests (FST) are the balance and coordination tests given to suspected drunk drivers on the roadside. Field tests are administered to help police determine if there is probable cause to make a DUI arrest. It is against the Fourth Amendment’s prohibition against unreasonable searches and seizures for police to pull someone out of a vehicle and arrest them for DUI without probable cause. The police need to build a case against the accused in order for the arrest to be lawful. Field tests perform this function. Pennsylvania police officers will evaluate a suspect’s performance on field tests to determine if there is probable cause to arrest a suspect for driving under the influence of alcohol.

There is no requirement in Pennsylvania that police perform field testing. Though, it is the best practice for police to administer field tests. In the event the suspect refuses the chemical test of blood, breath or urine back at the police station, field tests give the police “back up” evidence to present at trial.

Three field tests are approved by the National Highway Transportation Safety Administration (NHTSA) : the horizontal gaze nystagmus (HGN) test, one leg stand, and walk-and-turn tests.

Horizontal Gaze Nystagmus Test (HGN)

The HGN test measures rapid, uncontrollable and involuntary jerking movements of the eye. The police officer will instruct the DUI suspect to keep their head still and follow an object such as a flashlight, pen or fingertip. The officer will move the object smoothly side to side until the eye moves as far left or right as it can go. If the eye jumps uncontrollably as it is moving or while in the maximum horizontal position, this indicates to the officer that the suspect is under the influence of alcohol. Although there is a scientific evidence to back up the accuracy of the HGN test, it is my opinion that these tests are not admissible as evidence in Pennsylvania. If the prosecution attempts to admit an HGN test into evidence, the defense attorney should be jumping to his feet to object. Many cases by the Pennsylvania Superior Court have held that the Commonwealth’s evidence was insufficient to show that the HGN test was generally accepted in the scientific community as proof that a person is intoxicated. 1

One Leg Stand

In this test the police officer will ask the suspect to stand up straight, lift one leg about six inches off the ground with toes down and hold that stance for thirty seconds. The suspect should count out loud while performing the test. The police officer will look for the following clues to determine whether or not the suspect is intoxicated: hopping, swaying, moving arms out to maintain balance and putting foot down one or more times during the test. The results of this test may not be accurate in some test subjects. If the suspect is more than 50 pounds overweight, aged sixty or over or has a medical condition, he or she may not be able to perform this test satisfactorily.

Walk-and-Turn Test

In this test the suspect is asked to walk on a straight line taking nine heel-to-toe steps while counting each step aloud. After step nine, the suspect must pivot keeping one foot on the line, turn around and take nine more heel to toe steps while counting aloud in the opposite direction. During the test your arms should be at your side at all times. Pennsylvania police officers will look for the following clues that indicate the motorist is intoxicated: 1) starting the test during the officer’s instructions; 2) failure to touch heel to toe; 3) failure to balance; 4) walking off the line; 5) failure to keep the pivot foot on the line; 6) taking the incorrect number of steps; 7) raising arms from side to balance.

*Preliminary Breath Test (PBT)

This test is known as the “preliminary breath test,” “portable breath test” or “roadside breath test.” This test is given to the suspect on the side of the road and gives police a reading as to the suspects Blood Alcohol Concentration (BAC). This test should not be confused with the chemical test of blood, breath or urine given back at the police station or DUI processing center. The roadside breath test is not admissible in court to show the suspect’s BAC. It is merely a tool used by police to confirm the officer’s suspicions that the suspect was driving while intoxicated. It is a probable cause tool used by police to confirm suspicions of drinking and authorize the officer to make a DUI arrest. In a court hearing or trial, the test is only admissible to show the presence of alcohol. The police officer will not be allowed to state the actual reading of the instrument in open court.

Contact Us

If you or someone you know has been arrested for a Pennsylvania DUI based on field test results conducted by police, contact (link) my office to discuss the situation. You may be able to challenge the results of these field tests if you had a medical condition that prevented you from satisfactorily performing the tests, the police officer did not instruct you properly or the officer was overly aggressive in scoring your test. This list is not exhaustive and each case is unique. Contact my office to speak with Jason R. Antoine, former DUI prosecutor.


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See Commonwealth v. Apollo, 412 Pa. Super 453, 603 A.2d 1023 (1992); Commonwealth v. Stringer, 451 Pa.Super. 180, 678 A.2d 1200 (1996)