Marijuana and Actual Driving Performance
archive: archived pipeline: cataloged verified
Get this paper ↗ (full text — opens at the source; we link to it, we don't host it)
Summary
This report, sponsored by the U.S. National Highway Traffic Safety Administration (NHTSA) and conducted by the University of Limburg, investigates the dose-response relationship between tetrahydrocannabinol (THC) and actual driving performance. The research was motivated by inconclusive epidemiological data regarding marijuana’s contribution to traffic accidents and a need to objectively measure impairment in real-world conditions. The study aimed to determine if driving impairment correlates with plasma THC concentrations and to compare marijuana’s effects with those of alcohol. The research program comprised one pilot study and three actual driving studies involving recreational cannabis users. The pilot study established that users typically consume approximately 300 µg/kg of THC to achieve their desired effect, setting this as the maximum dose for subsequent trials. The first driving study tested doses of 0, 100, 200, and 300 µg/kg on a closed highway, measuring lateral position stability. The second study replicated this on a highway with other traffic, adding a car-following test to assess reaction times and headway maintenance. The third study compared a modest THC dose (100 µg/kg) against a low alcohol dose (BAC 0.04 g%) during urban city driving. All studies utilized double-blind, counterbalanced designs with licensed driving instructors ensuring safety. The findings indicate that marijuana produces a moderate, dose-related impairment in driving performance, primarily affecting the ability to maintain a steady lateral position (Standard Deviation of Lateral Position, SDLP). This impairment persisted for two hours post-smoking, even as plasma THC levels and subjective feelings of intoxication declined. The magnitude of impairment from 300 µg/kg THC was comparable to alcohol concentrations of 0.03–0.07 g%. In car-following tests, subjects increased their headway and reaction times, though these effects diminished with repeated exposure. Crucially, no significant correlation was found between plasma THC concentrations and driving impairment. In urban driving, alcohol significantly impaired performance, whereas marijuana did not; however, marijuana users reported higher effort levels, suggesting they compensated for their impairment. The study concludes that while THC impairs automatic information processing (lateral control), drivers retain insight into their condition and can compensate through increased effort or caution, particularly in tasks requiring controlled processing. Consequently, the adverse effects of THC on actual driving are relatively small compared to alcohol and many medicinal drugs. The results suggest that roadside sobriety tests and plasma measurements are poor predictors of actual driving impairment under the influence of marijuana.
Key finding
Marijuana produces a moderate, dose-related impairment in lateral position control that is significantly less than the impairment caused by alcohol at a blood alcohol concentration of 0.08 g%, with drivers compensating for deficits through increased effort and caution.
Methodology
on_road
Sample size: 70
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 |
|---|---|---|---|---|---|---|
| discover | success | rosap | — | — | 2 | 2026-05-23 |
| archive | success | — | — | — | 1 | 2026-05-23 |
| extract | success | cached | — | — | 2 | 2026-06-10 |
| clean | success | — | — | — | 1 | 2026-06-01 |
| chunk | success | — | — | — | 1 | 2026-06-01 |
| embed | success | — | — | — | 1 | 2026-06-02 |
| enrich | success | — | — | — | 1 | 2026-05-23 |
| promote | success | — | — | — | 1 | 2026-05-23 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 3 | 2026-06-10 |
| tag | success | vector_similarity | — | — | 19 | 2026-06-11 |
| verify | partial | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified_with_issues.
Topics
Ranked by relevance to this paper. Hover a topic for its definition.
Information type
What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).
- Methodological Resource: validation psychometrics