The Effect of Road Shoulder and Weather Conditions on the Occurrence of Rollover Crashes in Two-lane Highways
DOI: 10.3311/ppci.12588
archive: archived pipeline: cataloged verified
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Summary
This study investigates the impact of road shoulder characteristics and weather conditions on the occurrence of rollover crashes on two-lane highways. Motivated by the high danger and frequency of rollover incidents in such environments, the research aims to quantify how specific geometric and environmental factors influence crash probability. The authors focus exclusively on single-vehicle rollover crashes, excluding head-on and fixed-object collisions, to isolate the effects of roadway design and environmental conditions on vehicle stability. The analysis utilizes crash data recorded between 2006 and 2009 from six two-lane highways in central Iran. The dataset comprises 8,609 total crashes, of which 1,860 were identified as single-vehicle rollovers. The highways were classified into Class I (high-speed intercity routes) and Class II (lower-speed access routes). A binary logit model was employed to predict the likelihood of a rollover crash versus other crash types, using NLogit 5 software. The model included independent variables for highway class, road shoulder width, shoulder type (soil vs. asphalt), and weather/lighting conditions (rainy, snowy, foggy, and night). Variables were refined through a backward elimination process, retaining only those with statistical significance (p < 0.05). Shoulder type variables were merged into a discrete variable based on a 0.5-meter width threshold, as specific material types proved insignificant. The results indicate that adverse weather conditions have the most substantial impact on rollover crash occurrence. Rainy and foggy conditions yielded the highest positive coefficients (0.731 and 0.719, respectively), significantly increasing crash probability due to slippery surfaces and reduced visibility. Snowy conditions also increased risk (coefficient 0.303), though to a lesser extent, potentially due to increased driver caution. Nighttime conditions showed a moderate positive effect (0.184). Regarding geometric factors, narrower road shoulders (less than 0.5 meters) increased rollover probability (coefficient 0.221), while Class I highways showed a negative coefficient (-0.312), indicating a lower likelihood of rollovers compared to Class II highways, likely due to better pavement quality and higher traffic volumes. Sensitivity analysis revealed that the baseline probability of a rollover crash on these highways is 21.29%. Marginal effects showed that rainy and foggy conditions increase this probability by approximately 14.5% and 14.3%, respectively, while narrow shoulders increase it by 3.7%. The study concludes that weather conditions, particularly rain and fog, are the primary drivers of rollover crashes on two-lane highways, outweighing the influence of shoulder geometry. While shoulder width remains a significant factor, the type of shoulder material is not. The findings suggest that drivers must exercise heightened caution during rainy and foggy conditions. For infrastructure planning, the results imply that ensuring adequate shoulder width is beneficial for safety, but improvements in weather-related visibility and surface friction may offer greater reductions in rollover incidents. The study validates previous research linking narrower shoulders to higher crash rates while highlighting the critical role of environmental factors in single-vehicle crash dynamics.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | Crossref | — | — | 1 | 2026-06-18 |
| archive | success | canonical_url | — | — | 1 | 2026-06-25 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-18 |
| chunk | success | chunk | — | — | 1 | 2026-06-18 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-18 |
| promote | success | — | — | — | 1 | 2026-06-18 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-18 |
| verify | success | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.
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- Empirical Findings: crash risk outcomes