Evaluation of a County Enforcement Program with a Primary Seat Belt Ordinance: St. Louis County, Missouri
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Summary
This report evaluates the effectiveness of a high-visibility enforcement (HVE) campaign conducted in St. Louis County, Missouri, following the implementation of a primary seat belt ordinance in March 2007. The study was motivated by Missouri’s stagnant seat belt usage rates, which had plateaued at approximately 77% despite regular participation in national enforcement mobilizations. This rate lagged significantly behind the national average and the higher usage rates observed in states with primary enforcement laws. The research aimed to determine if intense enforcement under a primary ordinance could significantly increase usage and provide a benchmark for potential statewide law upgrades. The study employed a corridor-based experimental design comparing a target site against a control site. The target was an 8-mile segment of State Highway 21 in St. Louis County, selected due to a history of fatal and disabling injury crashes. The control site was a similar roadway, Highway 24, in Jackson County. In November 2008, the St. Louis County Police Department conducted a 13-day HVE campaign on the target corridor. The program involved saturation patrols and enforcement zones, resulting in 500 enforcement hours and nearly 1,000 citations issued, yielding a high citation rate of two per hour. Publicity was limited to roadway signage and variable message boards, with no paid media. Data collection included observational surveys of seat belt use at 15 sites and motorist awareness surveys conducted before and after the campaign. The results demonstrated significant positive impacts on both public perception and behavior. Awareness of seat belt enforcement on the target corridor increased by 60.5 percentage points, from 16.5% to 77.0%, compared to a negligible 9.3-point increase in the control area. Perceived risk of receiving a ticket and support for primary enforcement also rose significantly in the program area. Observed seat belt usage on Highway 21 increased by 4.9 percentage points, rising from 83.3% to 88.2%, while usage on the control corridor declined slightly. Notably, passenger usage increased by 6 points to nearly 90%, and usage among pickup truck occupants, a historically low-compliance group, improved significantly. The findings suggest that combining primary enforcement laws with regular HVE programs can substantially increase seat belt usage. The authors conclude that if Missouri enacted a statewide primary law and implemented similar HVE programs, it could save an estimated 30 to 70 lives annually, prevent 400 to 900 serious injuries, and reduce economic costs by $110 million to $215 million. The study supports the broader evidence that primary enforcement laws, when actively enforced, are more effective than secondary laws in promoting occupant protection.
Key finding
High-visibility enforcement in St. Louis County resulted in a 4.9 percentage point increase in seat belt usage on the targeted corridor compared to a control area.
Methodology
field_study
Sample size: 25877
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 |
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| 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 | — | — | 24 | 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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- Applied Guidance: countermeasure evaluation, policy recommendations
- Empirical Findings: observational prevalence