The Effect of Marihuana Dosage on Driver Performance
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Summary
This 1973 study by Moskowitz, McGlothlin, and Hulbert investigates the impact of marijuana dosage on driving performance, motivated by a lack of epidemiological data linking marijuana use to traffic accidents. The research aims to assess potential safety risks by examining how marijuana affects specific skills critical to driving, such as vehicle control and perceptual monitoring. The study employed two experiments involving 23 male college students with prior marijuana experience. The design used a double-blind, 4x4 Latin square structure with four treatment levels: placebo and three active doses of delta-9 tetrahydrocannabinol (THC) at 50, 100, and 200 micrograms per kilogram of body weight. The first experiment utilized a complex driving simulator featuring a real car mounted on a chassis dynamometer facing a 160-degree screen projecting a filmed 31-mile drive. Subjects controlled speed via accelerator and brake pedals and steering via a wheel that influenced the projected scene’s lateral movement. While tracking the road, subjects also performed a visual subsidiary task requiring rapid lever responses to light signals, simulating the search-and-recognition demands of real driving. The second experiment assessed auditory signal detection under conditions of concentrated and divided attention. Results from the driving simulator indicated that marijuana had little to no significant effect on car control and tracking measures, including speed, steering, and accelerator usage. Statistical analyses of 25 performance scores revealed no consistent trends or significant treatment effects for vehicle handling. However, marijuana caused a statistically significant, dose-related impairment in the visual subsidiary task. Higher doses led to increased reaction times and more errors in recognizing visual signals. For instance, mean reaction times for all responses increased by 5.3%, 10.6%, and 11.6% for the 50, 100, and 200 mcg/kg doses, respectively, compared to placebo. The second experiment on auditory signal detection confirmed these findings, showing a dose-related impairment in discrimination sensitivity rather than just a change in response criterion. The study concludes that while marijuana does not significantly impair the mechanical aspects of vehicle control or tracking in this simulator context, it substantially degrades perceptual functions, specifically the ability to search for and recognize environmental cues. This perceptual deficit is identified as a potential danger to driving safety, as such failures are cited as causes in nearly half of human-error-related accidents. The findings suggest that the primary risk of marijuana-impaired driving lies in reduced situational awareness and delayed recognition of hazards, rather than in the loss of steering or speed control capabilities.
Key finding
Marihuana produced a statistically significant, dose-related impairment in visual recognition reaction times and errors in a driving simulator, while car control and tracking performance remained unaffected.
Methodology
lab_experiment
Sample size: 23
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 | success | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
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Information type
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- Empirical Findings: behavioral performance data
- Methodological Resource: validation psychometrics