Influence of truck apron design on two-geometry roundabouts’ speed management potential
DOI: 10.5592/co/cetra.2024.1529
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Summary
This study investigates the influence of truck apron design on the speed management capabilities of two-geometry roundabouts, an alternative intersection design featuring an elliptical outer carriageway edge and a circular inner edge. These roundabouts are less bulky than standard designs, making them suitable for space-constrained locations. However, previous research indicates they require truck aprons to ensure vehicle trajectory deflection and necessary speed reduction for personal vehicles. Due to a lack of experimental data from constructed sites, the authors utilized computer simulations to analyze personal vehicle speed reduction and relative speeds between conflicting traffic streams. The methodology involved designing 40 single-lane, four-legged roundabout schemes using Autodesk AutoCAD 2021. This included 32 two-geometry roundabouts with major axes ranging from 18 to 25 meters and minor axes varying from 0.75 to 0.90 times the major axis length, plus eight standard modern roundabouts for comparison. Truck aprons were designed based on a 5-meter-wide circulatory lane, accommodating a standard European long vehicle (tractor with semitrailer) simulated via Autodesk Vehicle Tracking 2020. Expected driving speeds were estimated by constructing "fastest paths" for passenger vehicles, measuring path radii, and applying the FHWA speed-radius model. The results demonstrated that entry design speeds for the two-geometry roundabouts remained below the recommended maximum of 40 km/h for single-lane roundabouts, with only one standard roundabout scheme slightly exceeding this limit. Crucially, the relative speeds between consecutive geometric elements on all two-geometry schemes were below the recommended safety threshold of 15 km/h, whereas standard roundabouts showed a maximum relative speed of 16 km/h. Additionally, average expected driving speeds through the roundabouts were lower than 35 km/h, aligning with safety recommendations. The study found that relative speeds between conflicting traffic streams were higher on one approach compared to the other in two-geometry designs. The authors conclude that introducing truck aprons based on a 5-meter circulatory lane width provides sufficient vehicle speed reduction and consistency between consecutive geometric elements, thereby ensuring adequate traffic safety. This design allows two-geometry roundabouts to effectively manage speeds despite their compact footprint. The findings support the use of this design in constrained spaces, provided the truck apron is correctly sized. Future research is recommended to optimize circulatory lane widths further, investigating variable widths to determine limit values that maximize vehicle trajectory deviation and speed reduction.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | Crossref | — | — | 1 | 2026-06-25 |
| archive | success | canonical_url | — | — | 1 | 2026-06-26 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-25 |
| chunk | success | chunk | — | — | 1 | 2026-06-25 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-25 |
| promote | success | — | — | — | 1 | 2026-06-25 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-25 |
| verify | success | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.
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