Simulated surrogate measures to assess the effectiveness of countermeasures at signalized intersections
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Summary
This study addresses the limitations of traditional traffic safety assessments, which rely on historical crash data that is often sparse, underreported, and slow to collect. To overcome these issues, the authors propose using surrogate safety measures (SSMs) derived from traffic conflicts rather than actual crashes. The research aims to evaluate the safety of four four-legged signalized intersections in Diwaniya, Iraq, and assess the effectiveness of various countermeasures in reducing traffic conflicts. The methodology combines microscopic traffic simulation using PTV VISSIM software with the Surrogate Safety Assessment Model (SSAM). VISSIM was used to generate vehicle trajectory files based on collected field data, including traffic volumes, geometric characteristics, and signal timing. These trajectories were input into SSAM to identify and quantify traffic conflicts, specifically using Time to Collision (TTC) as the primary indicator. The model underwent rigorous calibration and validation processes. Calibration adjusted driving behavior parameters to match real-world conditions, reducing the Mean Absolute Percentage Error (MAPE) for total conflicts from 41.9% to 10.6%. Validation confirmed a strong correlation between simulated and observed conflicts, with a Pearson correlation coefficient of 0.954 for total conflicts at the Al-Oruba intersection. The study classified the intersections by risk level based on TTC values; Al-Jumhouri and Al-Oruba were identified as high-risk, while Al-Fadael and Al-Nesser were moderate-risk. Several countermeasures were simulated to determine their impact on safety, including increasing lane width, adding lanes, retiming traffic signals, adding left-turn phasing, and canceling U-turns. Results indicated that increasing the number of lanes was the most effective intervention, achieving a conflict reduction of up to 53.11% at the Al-Nesser intersection. Increasing lane width also proved highly effective, reducing conflicts by approximately 36–46% across the sites. Retiming signals and adding left-turn phasing yielded moderate reductions (26–45%), while canceling U-turns had the lowest impact, reducing conflicts by 21.5–30.9%. The findings demonstrate that simulation-based surrogate measures provide a reliable and efficient alternative to crash-based safety analysis, particularly in contexts where crash data is insufficient. The strong correlation between simulated and observed conflicts validates the use of VISSIM and SSAM for predictive safety assessments. The study concludes that geometric improvements, particularly increasing lane capacity, offer significant safety benefits at signalized intersections. This approach allows engineers to evaluate countermeasures rapidly without waiting for crash occurrences, facilitating proactive safety management and infrastructure planning.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | Crossref | — | — | 1 | 2026-06-20 |
| archive | success | canonical_url | — | — | 1 | 2026-06-26 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-20 |
| chunk | success | chunk | — | — | 1 | 2026-06-20 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-20 |
| promote | success | — | — | — | 1 | 2026-06-20 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-20 |
| verify | success | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.
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Information type
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- Applied Guidance: countermeasure evaluation
- Empirical Findings: crash risk outcomes
- Methodological Resource: validation psychometrics