Field sobriety testing
FSTs (and SFSTs) are primarily used in the United States and Canada, to meet "probable cause for arrest" requirements (or the equivalent in either country), necessary to sustain an alcohol-impaired driving (DWI or DUI) conviction based on a chemical blood alcohol test.
[1] According to the National Highway Traffic Safety Administration alcohol-related crashes cause approximately US$37 billion in damages annually.
A BAC or BrAC measurement in excess of the specific threshold level, such as 0.08%, defines the criminal offense with no need to prove impairment.
In addition, many countries have prevention campaigns that use advertising to make people aware of the danger of driving while impaired and the potential fines and criminal charges, discourage impaired driving, and encourage drivers to take taxis or public transport home after using alcohol or drugs.
Burns submitted a grant proposal in response to an RFP focused on creating standardized pre-arrest tools for police officers to use to decide which drivers were impaired.
[6] Her survey did find research by Penttilä, Tenhu, and Kataja, who did a retrospective study of the 15 tests then in use by Finnish law enforcement.
[6][7] Burns also examined officer training manuals[7] and went on ride-alongs with the DUI or special enforcement teams of several police departments.
[6] She conducted a series of pilot studies, statistical analyses, and practical considerations, and reduced this list to three "recommended" tests: the One-Leg Stand, Walk-and-Turn, and Alcohol Gaze Nystagmus.
[7][8] By 1981, officers in the United States began using this battery of standardized sobriety tests to help make decisions about whether to arrest suspected impaired drivers.
[10][11] The National Highway Traffic Safety Administration (NHTSA) has developed a model system for managing Standardized Field Sobriety Test (SFST) training.
FSTs and SFSTs are promoted as, "used to determine whether a subject is impaired",[12][13] but FST tests are widely regarded having, as their primary purpose, establishing tangible evidence of "probable cause for arrest" ("reasonable grounds" in Canada).
While the primary purpose of FSTs is to document probable cause or the equivalent, in some jurisdictions, FST performance can be introduced as corroborating evidence of impairment.
Nevertheless, these tests can be problematic for people with non-obvious disabilities affecting proprioception, such as Ehlers-Danlos syndrome (EDS).
The tests were not validated for people with medical conditions, injuries, 65 years or older, and 50 pounds or greater overweight.
[23] The police may also then check for Vertical Gaze Nystagmus, which is used to test for high blood alcohol levels and/or the presence of certain drugs.
While the purpose is obtaining probable cause support for an arrest and possibly screening, in some jurisdictions, the HGN test may be used as corroborating evidence at the trial stage.
[25] This test measures the suspect's ability to maintain their balance, walk in a straight line, and follow directions.
While the suspect performs this test, the officer is attempting to observe if the suspect fails to follow instructions; is having difficulty keeping their balance; stops walking in order to regain their balance; takes an incorrect number of steps; or fails to walk the line heel-to-toe.
The individual is supposed to walk heel to toe, and while looking down at a real or imaginary line, count the steps out loud.
The proper instruction, according to the NHTSA Guidelines, is as follows: The other standardized test is the One Leg Stand (OLS).
[7] Nevertheless, these tests are common in North America, because the primary purpose of FSTs is to establish probable cause to sustain an arrest and invoke the implied consent law, and thus they do not need to be scientifically validated.
One of the common challenges of field sobriety tests is that FSTs are considered subjective - the judgment is left up to the discretion of the police officer.
[30] It is almost impossible to tell whether or not a police officer used proper procedures for administering or judging the field sobriety test when a case is brought to court without body camera recordings.
[32] One author alleges that FSD analysis reports do not meet scientific peer review standards: "The reports for all three studies issued by NHTSA are lacking much of the material and analysis expected in a scientific paper, and none have been published in peer-reviewed journals" (Rubenzer 2008;[30] Rubenzer 2011).
In the opinion of the re-analysis authors, these tests are so weak that they do not substantially change the certainty of intoxication beyond the uncertainty of the original guesstimate.
As noted above, these tests can be problematic for people with non-obvious disabilities affecting proprioception, such as Ehlers-Danlos syndrome (EDS).
[30] The NHTSA used to say that those who are 50 pounds or more overweight may have difficulty performing the test, and that the suspect must walk along a real line.
[32] The fact that officers are no longer required to provide a line for the suspect to walk along may affect the outcome of the test, and often adds to the scrutiny received from critics.
[36] If over the legal limit of 0.05g per 100 millilitres of blood, then a second breath test will be taken and used as evidence against the driver when charged with the offence.
FSTs are requested in the 'police stop' phase, and are used to provide tangible evidence sufficient to meet the requirements for 'probable cause' for an arrest.
