Law and Science of Driving Under the Influence

Abstract

Driving under the influence (DUI) of drugs and alcohol is a serious public health problem in the developed world and prohibited by law in virtually all jurisdictions. Historically, while moderate alcohol usage has generally been socially acceptable, impairment due to excessive use of alcohol, while operating a vehicle, is a serious criminal offense, proven through forensic alcohol analysis and field sobriety testing.

While impairing in itself at excess concentrations, alcohol’s metabolites can also have serious detrimental cognitive effects and be responsible for potentially deadly long-term illnesses. Forensic extrapolation of blood alcohol content (BAC) is chiefly obtained from samples of the subject’s breath, that methodology potentially being impacted by other substances and extraneous environmental factors. While an inference of impairment may be drawn solely from BAC, analysis of certain standard field sobriety tests (SFSTs) generally has been shown to be sensitive in ascertaining whether a driver is intoxicated. Both forensic BAC analysis and SFST, however, even when suggestive of alcohol-related impairment, are not specific for it. A DUI charge has significant occupational, legal, financial, and administrative ramifications, such that proper analysis is essential, not only to identify and deter the impaired but to protect the innocently accused.

BAC measurements implying impairment vary in different jurisdictions but generally have trended downward. Prosecutors, hard at work to deter and punish drunk drivers, are countered by a defense bar properly analyzing the probable cause necessary to detain a driver and subsequently administer the SFSTs in addition to the science behind the forensic alcohol analysis and any factors that might wrongfully convict the innocent. Various constitutional and statutory defenses are available on the criminal side, while more limited challenges can be made on the administrative side. Virtually all convicted offenders lose their license to operate a motor vehicle, at a minimum temporarily.

DUI arrests actually occur in a fairly small and predictable number of scenarios, each lending itself to different defenses and prosecutorial theories, the most serious being those involving death or serious injury. The pitfalls and subjectivity of SFST underscore the importance of reliable and reproducible forensic analysis, a typical DUI trial pitting the police and prosecutors attempting to validate each and every procedural step in the arrest, while the defense seeks to find a scintilla of reasonable doubt at those same steps. Whether procedural, statutory, constitutional, or forensic, every facet of the DUI arrest will be dissected.

DUI is a potentially life-changing experience, affecting the individual defendant and having broad impact on society as a whole. Education and avoidance, the lynchpins of curbing impaired driving, come only at a cost, with society’s jury still out on how best to implement deterrence and who will be responsible for paying for it.