Virginia DWI law does not support assuming dissipating alcohol content, let alone using retrograde extrapolation

Virginia DWI law does not support assuming that a driver’s blood alcohol content was higher at the time of driving than at the time of blood alcohol content (BAC) testing via obtaining a breath or blood sample. As a Fairfax DUI lawyer, I know from working with forensic science experts and reviewing the literature that, after consuming alcohol, a Virginia DUI suspect’s blood alcohol level starts rising as alcohol absorbs into the bloodstream, then plateaus and then dissipates. This truism plus the numerous variables referenced below, mean the Virginia law does not support precluding consideration that one’s blood alcohol level was lower at the time of driving than at the time of testing, and should not allow retrograde extrapolation, whereby a prosecution expert witness opines the extent to which the DUI defendant’s blood alcohol level was actually higher at the time of driving than at the time of BAC testing.

What are the seminal Virginia court cases that govern when to consider BAC at time of driving and time of testing?

Discussed below are the two key Virginia DWI law cases governing when and how to consider blood alcohol content at the time of driving and testing. The Virginia DUI / driving under the influence of alcohol or drugs statutory scheme at Va. Code §§ 18.2-266 and 18.2-269 provides for presumptions that may be drawn from breath and blood testing, but only as a permissive inference and not a rebuttable presumption. Yap v. Com., 49 Va. App. 622, 631 ( 2007). The overall language of Yap provides for BAC at the time of driving to be able to be lower than at the time of testing.

Moreover, reading the foregoing Virginia DWI law Yap decision with the following Wimbish decision, for alleged BAC’s under 0.15, the BAC at the time of driving is what governs, and alleged BAC’s of 0.15 consider the BAC at the time of testing. See Yap, supra, and Wimbish v. Commonwealth of Virginia court case (51 Va. App. 474 (2008)).

Why retrograde extrapolation is not supported by Virginia DWI law

Retrograde extrapolation is not supported by Virginia DWI law, nor by the Due Process Clauses of the federal Constitution’s Fifth and Fourteenth Amendments, based on the above considerations, and the persuasive studies linked as follows by Pharmacology expert Alan W. Jones (“Alcohol, its absorption, distribution, metabolism, and excretion in the body and pharmacokinetic calculations (May 2019, Wiley Interdisciplinary Reviews Forensic Science 1(5):e1340),and forensic toxicologist Kurt M. Dubowski (“Absorption, distribution and elimination of alcohol: Highway safety aspects” (August 1985, Journal of studies on alcohol, supplement 10(s10):98-108), including his graphs as page 104 showing how BAC first rises before it plateaus and dissipates. Moreover,  retrograde extrapolation is all the more unreliable when considering that alcohol absorption rates are affected by such factors as when alcohol consumption began, food intake factors, adiposity, age and gender.

Virginia DUI lawyer Jonathan Katz has successfully defended hundreds of people charged with driving under the influence of drugs and/or alcohol. See the positive difference Jon Katz can make to your defense with a free in-person confidential consultation scheduled through Jon’s staff at 703-383-1100.