Evaluation of Michigan’s engineering improvements for older drivers.
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Summary
This study evaluates the safety effectiveness and economic viability of five engineering countermeasures implemented by the Michigan Department of Transportation (MDOT) to address the needs of older drivers (age 65 and older). Motivated by a 2.4% increase in crash involvement for older drivers and a 15.9% rise in fatal crashes involving this demographic between 2004 and 2013, the research assesses Clearview font on guide signs, box span signal installations, pedestrian countdown signals, fluorescent yellow sheeting on warning signs, and arrow-per-lane signing. The primary objectives were to quantify safety benefits for all drivers and older drivers specifically, and to develop Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) for these treatments. The methodology combined a perception survey of 1,590 Michigan drivers across four metro areas with a rigorous analysis of crash data. Researchers developed SPFs using Negative Binomial models for freeway and non-freeway segments, identifying significant variables such as Average Annual Daily Traffic (AADT), segment length, and access points. CMFs were estimated using the Empirical Bayes method where reliable SPFs existed, and the Before-After with Comparison Group method otherwise. Due to simultaneous installation, Clearview font and fluorescent yellow sheeting were evaluated jointly. Benefit-cost analyses were conducted using differential installation costs and estimated crash savings. The findings indicate that all five countermeasures improve safety for both older drivers and the general driving population. Survey results showed strong driver preference for most improvements, with box span signals specifically noted for improving signal visibility and lane identification. Quantitative analysis yielded CMFs less than 1.0 for all treatments, indicating crash reduction. For example, the combined Clearview and fluorescent yellow treatment on urban non-freeways resulted in a CMF of 0.704 for all severities. Box span signals reduced angle crashes involving older drivers significantly (CMF 0.477). Pedestrian countdown signals showed a CMF of 0.683 for all pedestrian crashes. The economic analysis revealed that all countermeasures are highly cost-effective, with benefit-cost ratios ranging from 13:1 for box span signals to 7,456:1 for the combined sign treatments on urban non-freeways. The study concludes that these engineering improvements provide substantial safety benefits that outweigh their costs, justifying replacement before the end of their service life. The development of specific SPFs and CMFs provides MDOT with validated tools for future safety planning and the Highway Safety Manual spreadsheet. The results support the continued systemic application of these countermeasures to mitigate the rising crash rates among older road users.
Key finding
All five evaluated engineering countermeasures significantly reduced crash frequencies for older and general drivers, with benefit-cost ratios ranging from 13:1 to 7,456:1.
Methodology
mixed_methods
Sample size: 1590
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.
Topics
Ranked by relevance to this paper. Hover a topic for its definition.
- roadway lighting effects
- signage environment
- perceptual countermeasures
- incidence prevalence
- rail grade crossings
- sign visibility legibility
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).
- Applied Guidance: countermeasure evaluation
- Empirical Findings: crash risk outcomes
- Methodological Resource: dataset resource