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August 2010Volume 20Number 1PDF icon PDF version (for best printing)

Back to the basics: Challenging the accuracy of field sobriety tests

Scenario: Police officer observes Defendant’s vehicle speeding and initiates a traffic stop on the vehicle. Based on observations made after the stop the officer conducts a DUI investigation. Defendant submits to standardized field sobriety tests including the Horizontal Gaze Nystagmus test [“HGN”]. Defendant is arrested and charged with various offenses of the Illinois Vehicle Code including but not limited to Driving Under the Influence of Alcohol in violation of 625 ILCS 5/11-501(a)(1), (2). Defendant files a motion to quash arrest and suppress evidence. At the hearing, the officer testifies that he administered the tests according to how he was trained but admits that he was not trained in accordance with the standardized field training manual used by the National Highway Traffic Safety Administration (“NHTSA Testing Manual”).1 The issue raised in this scenario is not whether the test results are admissible, but rather, whether or not they are reliable based upon the officer’s admission that he does not administer the tests according to NHTSA standards.


Generally, in order for a “test” to be considered valid, it must be supported by a reasonable degree of validity in accordance with Frye v. United States, 293 F.2d 1013 (D.C. Cir 1923). In 1977, the National Highway Traffic Safety Administration commissioned the Southern California Research Institute to determine the best method for detecting drunk drivers through the use of field sobriety tests and that study revealed that the HGN test, when used with the walk-and-turn and one-leg stand tests, is the most accurate and effective method of detecting alcohol impairment. People v. Robinson, 349 Ill. App. 3d 622, 812 N.E.2d 448, 456 (1st Dist., 2004).2 In fact, a subsequent study revealed that of the three field sobriety tests, the HGN test was the most powerful. Id.3 Furthermore, according to the United States Department of Transportation Test Manual, as devised for use by law enforcement agencies, the HGN test is “the single most accurate field test used in determining whether a person is alcohol impaired.” United States Department of Transportation, National Highway Safety Administration, Improved Sobriety Testing 4 (1984), as cited in State v. Bresson, 51 Ohio St.3d 123, 125, 554 N.E.2d 1330, 1332 (1990); See also, Robinson. The results of an HGN test are not conclusive, however, and can only be considered along with other evidence of intoxication. Id at 546.

In Illinois, the HGN test was found to meet the Frye standard in People v. Buening, 229 Ill.App.3d 538, 592 N.E.2d 1222 (1992). That decision, in turn, was followed by the appellate court in People v. Wiebler, 266 Ill.App.3d 336, 339, 640 N.E.2d 24 (1994).

In the wake of Buening and Wiebler, HGN test results have been routinely admitted in prosecutions for driving under the influence…. Although the State is no longer required to show that the HGN test satisfies the Frye standard before it may introduce the results of an HGN test into evidence, the validity of HGN tests and test results is not beyond challenge. If a defendant has evidence showing that HGN tests are unsound, then he may interpose the appropriate objection to the HGN test results and present his supporting evidence to the trial court. If the trial court is persuaded by the defendant’s evidence, then the court has the right to bar its admission. Note, however, that it is the defendant’s obligation to show that the test results are infirm. It is not the responsibility of the State to show that the tests and results are scientifically valid. Absent proof by the defense that the HGN test is unsound, the State need only show that the officer who gave the test was trained in the procedure and that the test was properly administered.

People v. Basler, 193 Ill. 2d 545, 740 N.E. 2d 1, 4 (Ill., 2000) (emphasis added). Thus, for HGN test results to be admissible, a proper foundation requires testimony concerning the officer’s education and experience in administering the test and a demonstration or explanation that the procedure was properly administered. People v. Buening, 229 Ill.App.3d at 546, 592 N.E.2d 1222 (1992). Once a proper foundation has been laid, the results of that test may be admitted as evidence of consumption of alcohol but may NOT be used to establish that the defendant’s blood alcohol concentration was at or above a certain level. See People v. Dakuras, 172 Ill. App. 3d 865, 527 N.E.2d 163 (2d. Dist. 1988) (holding that the HGN test was inadmissible to prove a blood alcohol concentration due to Section 11-501.2 of the Illinois Motor Vehicle Code, which restricts proof of blood alcohol concentrations to specific analyses of blood, breath or urine only). For example, the police officer’s testimony regarding the results of a defendant’s failed HGN test tends to show that he or she consumed alcohol prior to being tested. Similarly, testimony that a defendant did not display any sign of HGN is relevant evidence that tends to show that he or she had not consumed alcohol. The result of the test, therefore, makes it either more or less likely that a defendant was impaired due to [consumption of] alcohol.” People v. McKown, Docket No. 102372, pg. 20 (Ill. 2/19/2010) (Ill., 2010).

Illinois recognized and adopted the NHTSA protocol for field sobriety testing in People v. McKown, Docket No. 102372 (Ill. 2/19/2010) (Ill., 2010). In that case, the Illinois Supreme Court affirmed Basler with regard to the admissibility of HGN testing holding that “HGN testing is generally accepted in the relevant scientific fields as evidence of alcohol consumption and possible impairment” and adopted “the trial court’s five conclusions of law regarding the admission of HGN evidence and its use at trial.”4 Id. pg. 28. The Court further held that “evidence of HGN field-sobriety testing, when performed according to the NHTSA protocol by a properly trained officer, is admissible under the Frye test for the purpose of showing whether the subject has likely consumed alcohol and may be impaired. As for the qualifications of the individual witness, the trial court concluded that a proper foundation must be laid, including a showing that the witness is properly trained and that he performed the test in accordance with proper procedures.” Id. pg. 21.

The proper method for conducting HGN testing in the field, and the qualifications of the witness, requires that the HGN testing was performed according to the NHTSA standard testing protocol as developed and taught by NHTSA. McKown, Docket No. 102372, pg. 21. Thus, the Court limited Frye admissibility to only those HGN test results that followed the NHTSA standard testing protocol. The Court further noted that “the use of HGN evidence should be limited to proof of alcohol consumption and the possibility of resulting impairment. Limitation may take the form of sustaining an objection to certain questions or arguments made by the prosecutor, giving a limiting instruction at the time the testimony is given, or giving a written jury instruction at the conclusion of the case.” Id. pg. 20.

With regard to the admissibility of a defendant’s performance of physical field sobriety tests, including the Walk-and-Turn Test and One-Legged Stand Test, and the admissibility of testimony interpreting the results of those tests, Illinois courts have been reluctant to require the same quantum of training as with the HGN. This distinction was addressed in People v. Sides, where the Court explained that the ‘finger-to-nose test’, the ‘walk-and-turn test,’ and the ‘one-leg stand test’ (sic) “were not so abstruse as to require a foundation other than the experience of the officer administering them.” 199 Ill. App. 3d 203, 556 N.E. 2d 778, 779 (4th Dist. 1990) citing People v. Vega, 145 Ill.App.3d 996, 1000-01, 496 N.E.2d 501 (1986) (emphasis added). Similarly, in People v. Bostelman, 325 Ill.App.3d 22, 756 N.E.2d 953, 961 (2d Dist. 2001), the Court concluded that an officer is not required to establish that he has any previous experience or formal training in the administration of field sobriety tests in order to testify about the defendant’s performance on field sobriety tests.

In light of the decision in McKown, however, defendants should renew their arguments to extend the principles and guidelines set forth by the U.S. Department of Transportation, as well as the recent Illinois Supreme Court decisions of Basler and McKown, to other field sobriety tests. Indeed, it would be inconsistent for courts to disregard the clear directive of the Supreme Court in finding that the NHTSA guidelines should be strictly followed with regard to HGN testing and not extend those same principles to other field sobriety testing—especially where those tests have a lower accuracy rate than the HGN.5 Failure to follow the NHTSA testing guidelines also contradicts everything that the officers are taught and arguably renders the NHTSA Testing Manual irrelevant. As if to emphasize how important it is to follow the guidelines without deviation, the NHTSA Testing Manual unambiguously states that, “if any one of the standardized field sobriety test elements is changed, the validity is comprised.” NHTSA Testing Manual at VIII-19 (emphasis in the original). Similarly, the Illinois Local Governmental Law Enforcement Officers Training Board and the Illinois Department of Transportation, in conjunction with the Illinois State Police, have produced a Field Sobriety Training Manual, which is based upon the NHTSA standards. Page 9 of that manual states “If the standardized administration and scoring procedures presented in this manual are not followed, then the decision-making guidelines are no longer accurate.” The Illinois State Police Breath Analysis Unit also has a Field Sobriety Manual, which adopts the NHTSA standards. Page 12 of that manual states that “If the standardized administration and scoring procedures presented in this manual are not followed, then the decision-making guidelines are no longer accurate.” Clearly, these guidelines were intended to be followed.

Other jurisdictions have held that standard field sobriety tests conducted in a manner that departs from the methods established by the National Highway Traffic Safety Administration “NHTSA” are inherently unreliable. See State v. Homan, 89 Ohio St. 3d 421, 732 N.E.2d 952, (Ohio, 2000).6 In Homan, the Ohio Supreme Court opined that, in administering field sobriety tests, the police must strictly comply with established standardized procedures. Homan, 89 Ohio St.3d at 427. In that case, the Trooper testified on cross-examination that “at times he deviated from established testing procedures.” Id. The court held that when administering field sobriety tests there must be strict compliance with the standardized testing procedures set forth in the National Highway Traffic Safety Administration (NHTSA) Student Manual, Id. at 425. Therefore, even though field sobriety tests may be valid and admissible when strictly administered and scored, any deviation from the approved/standardized administration procedure rendered the results unreliable and therefore subject to bar.

While field sobriety tests must be administered in strict compliance with standardized procedures, probable cause to arrest does not necessarily have to be based, in whole or in part, upon a suspect’s poor performance on one or more of these tests. The totality of the facts and circumstances can still support a finding of probable cause to arrest even where no field sobriety tests were administered or where the test results must be excluded for lack of strict compliance. That is where the officer’s note taking skills7 become critically important.8


The admissibility of standardized field-sobriety testing, including HGN evidence, in an individual case will depend on the State’s ability to lay a proper foundation and to demonstrate the qualifications of its witness, subject to the balancing of probative value with the risk of unfair prejudice.  The small margins of error that characterize field sobriety tests make strict compliance with standard testing protocol critical. For example, in Homan, the arresting officer’s failure to use the full four seconds when checking for the onset of nystagmus, while seemingly trivial, rendered the results of that test unreliable.

In this scenario, Defendant should argue that the field sobriety test results, particularly that of the HGN test, should be excluded because the officer was not properly trained in accordance with the standardized field training manual used by the National Highway Traffic Safety Administration (NHTSA) and, therefore, the validity of the results are compromised. For the reasons stated above, Defendant may move to quash arrest and suppress evidence of any field sobriety testing unless such test results have been established as reliable by proof that there was strict compliance with the standardized procedures for administering the tests. Finally, Defendant should move in limine to limit the testimony of police officers to actual observations only, and prohibit such terms as pass, fail, etc., because such terms are prejudicial, misleading and invade the province of the trier of fact. See Sides. ■


1. U.S. Department of Transportation HS 178 R2/06, DWI Detection and Standardized Field Sobriety Testing, Student Manual (2006).

2. Citing National Highway Traffic Safety Administration, U.S. Department of Transportation, Psychophysical Tests for DWI Arrests, No. DOT-HS-802-424 at 39 (June 1977).

3. Citing National Highway Traffic Safety Administration, U.S. Department of Transportation, Field Evaluation of a Behavioral Test Battery for DWI, No. DOT-HS-806,475 at 4 (September 1983).

4. 1. HGN testing satisfies the Frye standard in Illinois. 2. HGN testing is but one facet of field sobriety testing and is admissible as a factor to be considered by the trier-of-fact on the issue of alcohol or drug impairment. 3. A proper foundation must include that the witness has been adequately trained, has conducted testing and assessment in accordance with the training, and that he administered the particular test in accordance with his training and proper procedures. 4. Testimony regarding HGN testing results should be limited to the conclusion that a “failed” test suggests that the subject may have consumed alcohol and may [have] be[en] under the influence. There should be no attempt to correlate the test results with any particular blood-alcohol level or range or level of intoxication. 5. In conjunction with other evidence, HGN may be used as a part of the police officer’s opinion that the subject [was] under the influence and impaired.

5. NHTSA analyzed the Laboratory and field-testing test data of sobriety tests and determined that:

a) the HGN by itself was 77% accurate

b) the Walk-and-Turn by itself was 68% accurate

c) the One-Legged Stand by itself was 65% accurate

6. The National Traffic Law Center (NTLC) has a list of every state’s Appellate Court/Supreme Court cases addressing HGN and SFST issues. The materials are available to law enforcement at <> or by phone (703) 549-4253.

7. “The evidence gathered during the detection process must establish the elements of the violation and must be documented to support successful prosecution of the violator.” NHTSA Testing Manual, pg. IV-7.

8. Field notes may be subpoenaed as evidence in court.

Member Comments (1)

Wonderful article. There is a trend across the country to require that all forensic tests be scientifically valid and reliable, and supported by verifiable scientific data. A start in that direction here would be to force the police to strictly comply with the NHTSA guidelines, before prosecutors can be allowed to argue that the results of such tests are reliable and capable of proving intoxication to any degree.

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