Report on a National Study of Preliminary Breath Test (PBT) and Illegal per Se Laws: Effectiveness of PBT & IPS Laws
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Summary
This 1981 report, commissioned by the National Highway Traffic Safety Administration (NHTSA) and conducted by Science Applications, Inc., evaluates the effectiveness of two specific legislative countermeasures for Driving While Intoxicated (DWI) offenses: Illegal Per Se (IPS) laws and Preliminary Breath Test (PBT) laws. The study aims to provide state governments and traffic safety organizations with data-driven recommendations to improve DWI enforcement and adjudication. IPS laws establish strict liability for driving with a blood alcohol concentration (BAC) of 0.10 percent or higher, removing the need to prove subjective impairment. PBT laws authorize police to administer breath tests prior to arrest to establish probable cause. The methodology involved a comprehensive national survey of all states with enacted IPS or PBT statutes, as well as states that had attempted but failed to pass such legislation. The researchers conducted in-depth case studies in six states with these laws (Nebraska, Minnesota, Florida, Virginia, Washington, and Oregon) and one state without them (California). Data collection included legal analysis of statutory provisions and case law, interviews with police, prosecutors, defense attorneys, and judges, and a review of statistical data regarding arrests and convictions. The study also incorporated findings from an NHTSA-sponsored workshop attended by national authorities on IPS and PBT laws. The findings indicate that IPS laws significantly enhance the prosecution of DWI offenses. The report documents that IPS statutes increased guilty pleas by an estimated average of 12 percent across jurisdictions, with Alabama reporting a 40 percent increase in the first six months after implementation. IPS laws also reduced the number of DWI charges negotiated down to lesser offenses by an average of 16 percent and increased overall DWI convictions by an estimated 9 percent. Prosecutors reported that IPS facilitated faster case settlements and reduced prosecution costs by lowering the number of trials. Furthermore, IPS laws assisted law enforcement in making arrests based on objective BAC levels rather than subjective observations of impairment, particularly for drivers showing few outward signs of intoxication. The report found no offsetting disadvantages to IPS laws. The significance of this study lies in its provision of model statutory language and jury instructions for IPS and PBT laws, designed to be acceptable to most state legislatures. The report concludes that IPS provisions are effective tools for enforcing drunk driving laws, facilitating prosecution by reducing the elements required to prove guilt and providing a clear, objective basis for arrest. The findings support the adoption of these laws to improve highway safety, streamline legal processes, and increase conviction rates for impaired drivers. The report serves as a practical guide for legislative analysis, addressing legal, constitutional, and tactical issues associated with implementing these statutes.
Key finding
Illegal Per Se laws increased guilty pleas by an estimated average of 12 percent, reduced charges negotiated down to lesser offenses by 16 percent, and increased DWI convictions by 9 percent.
Methodology
mixed_methods
Provenance
The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).
| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
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