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Presumptions of Impairment

Under Florida law, the result of a breath test reading may lead to certain "presumption of impairment" being applied in the case. The presumptions define impairment and emphasize the scientific value of breath testing evidence.

If the case goes to trial, the presumptions of impairment are explained to the jury if the breath test results are admitted into evidence and the prosecutor is arguing that the defendant's "normal faculties" were impaired. The jury is told that the presumptions are not conclusive.

The jury is told that the presumptions are not conclusive. Instead, the jury will ultimately decide whether to accept or reject the legal presumptions depending on the other evidence in the case. The other evidence might be sufficient to overcome the presumption of impairment. That other evidence can include the defendant's driving pattern, the odor of alcohol, the defendant's appearance, behavior, movements, and speech.

That other evidence can include the defendant's driving pattern, the odor of alcohol, the defendant's appearance, behavior, movements, and speech.

In Florida, the "per se" version of DUI requires proof of what the BAC level was at the time of driving or actual physical control of the vehicle. Of course, the breath test is often taken an hour later at the police station. The presumptions of impairment also apply to the BAC at the time of driving or being in control of the vehicle.

From the time of driving until the time of testing, the BAC can either continue to rise as alcohol is being absorbed in the body or it can begin to fall. In some cases, the state or defense will call an expert to explain how the BAC at the time of testing can be used to estimate the BAC at the time of driving (often called "retrograde extrapolation").

The presumptions of impairment can be used by either the prosecution when the BAC is over .08 or by the defense when the BAC is under .08. The presumptions can be rebutted with other evidence including the fact that the defendant didn't look impaired.


"Prima Facie Evidence of Impairment" in § 316.1934(2)(c)

Under Florida law, it is not necessary to instruct on the "prima facie evidence of impairment" in § 316.1934(2)(c), Fla. Stat., if the State charged the defendant with driving with a blood or breath-alcohol level of .08 or over and doesn't allege that the defendant's normal faculties were actually impaired.

In those cases, if the jury finds that the defendant drove with an unlawful blood or breath-alcohol level, showing actual impairment becomes moot. Tyner v. State, 805 So. 2d 862 (Fla. 2d DCA 2001). In these cases, the criminal defense attorney can still argue that the lack of evidence showing any impairment also demonstrates that the BAC reading is not accurate.


Florida's Standard Jury Instructions for Impairment Presumptions

One of the best ways to understand the presumptions of impairment under Florida law is to read the standard jury instructions that are often given at trial under Florida Statute Section 316.1934(2)(a), (b) or (c).

  • Breath of Blood Test Reading of .05 or Less - If you find from the evidence that while driving or in actual physical control of a motor vehicle, the defendant had a blood or breath-alcohol level of .05 or less, you shall presume that the defendant was not under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired; but this presumption may be overcome by other evidence demonstrating that the defendant was under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired.
  • Breath of Blood Test Reading of more than .05 but less than .08 - If you find from the evidence that while driving or in actual physical control of a motor vehicle, the defendant had a blood or breath-alcohol level in excess of .05 but less than .08, that fact does not give rise to any presumption that the defendant was or was not under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired. In such cases, you may consider that evidence along with other evidence in determining whether the defendant was under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired.
  • Breath or Blood Test Reading of .08 or More - If you find from the evidence that while driving or in actual physical control of a motor vehicle, the defendant had a blood or breath-alcohol level of .08 or more, that evidence would be sufficient by itself to establish that the defendant was under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired. But this evidence may be contradicted or rebutted by other evidence demonstrating that the defendant was not under the influence of alcoholic beverages to the extent that the defendant's normal faculties were impaired.

Classifications of Rebuttable Presumptions under Florida Law

Under Florida Statute Section 90.302, every rebuttable presumption is classified as either:

  1. A presumption affecting the burden of producing evidence and requiring the trier of fact to assume the existence of the presumed fact, unless credible evidence sufficient to sustain a finding of the nonexistence of the presumed fact is introduced, in which event, the existence or nonexistence of the presumed fact shall be determined from the evidence without regard to the presumption; or
  2. A presumption affecting the burden of proof that imposes upon the party against whom it operates the burden of proof concerning the nonexistence of the presumed fact.

Additional Resources

Florida Statute 316.1934 on Presumption of Impairment - Visit Online Sunshine, the official website of the Florida Legislature to find Florida Statute Section 316.1934 on the impairment presumptions and BAC testing methods. The statute on the presumption of impairment can apply to both civil or criminal action or proceeding arising out of acts alleged to have been committed by any person who was DUI to the extent that the person’s normal faculties were impaired. The statute provides that if there was a BAC of 0.08 or higher, that fact is prima facie evidence that the person was under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired.


Understanding Florida's DUI Impairment Presumptions

Contact one of the four Tampa DUI Attorneys at the Sammis Law Firm so that you can understand how the presumptions of impairment (or lack thereof) might affect your DUI or drunk driving case throughout the greater Tampa Bay area, including Tampa and Plant City in Hillsborough County, FL.

Contact us to discuss the charges pending against you, the elements of that offense that must be proven at trial, and the best defenses that can be used to fight the charges.

Call 813-250-0500 to discuss the particular facts of your case directly with an experienced criminal defense attorney today.


This article was last updated on Thursday, November 15, 2018.