Estimation of Air Pollutant Emissions in Flower Roundabouts and in Conventional Roundabouts
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Summary
This paper addresses the estimation of air pollutant emissions, capacity, and delay in flower roundabouts compared to conventional roundabouts. The research is motivated by the need to evaluate the environmental and functional performance of flower roundabouts, a specific intersection design that separates right-turning vehicles into a free-flowing bypass lane to reduce conflicts within the circulatory ring. The authors aim to determine if this geometric innovation offers advantages in terms of traffic efficiency and reduced vehicular emissions, particularly in urban contexts where road infrastructure significantly impacts air quality. The study employs a modeling approach to estimate lane capacities, delays, queue lengths, and levels of service for both flower and conventional roundabouts. Capacity calculations are performed lane-by-lane, accounting for different traffic regulations (stop, yield, or free flow) for the right-turn bypass lanes and utilizing the HCM 2010 methodology for through and left-turn lanes. The model also incorporates the impact of pedestrian flows on vehicle capacity using reduction factors derived from German methods. To estimate pollutant emissions, the authors use the COPERT software, a European tool for calculating emissions from road transport. This software calculates emission factors for carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), nitrogen oxides (NO), and particulate matter (PM2.5 and PM10) based on vehicle types, fleet composition, and traffic parameters such as speed and acceleration. The comparative analysis evaluates six geometric layouts: flower roundabouts with stop, yield, or free-flow slip lanes, and conventional roundabouts with varying lane configurations (single or double lanes at entries and rings). The study analyzes specific traffic conditions, including hourly origin-destination matrices and pedestrian flows indicative of peak hours. Results indicate that flower roundabouts and double-lane conventional roundabouts provide better performance in terms of mean control delay and average speed compared to single-lane conventional roundabouts. Specifically, flower roundabouts are advantageous when circulating flows are modest or moderate (below 1,600 veh/h) and when a significant portion of traffic turns right. However, they are unsuitable for high circulating flows exceeding this threshold, where conventional large-sized roundabouts are more appropriate. The emission analysis demonstrates that the reduction in delay and improvement in traffic flow associated with flower roundabouts can lead to lower vehicular emissions compared to less efficient conventional designs, provided the traffic conditions align with the design's capacity constraints. The significance of this work lies in providing a comprehensive model for assessing the environmental and operational impacts of flower roundabouts. It highlights that while flower roundabouts can enhance safety and reduce emissions by minimizing conflicts and delays, their application is limited by circulating flow volumes. The findings support the use of flower roundabouts in specific urban scenarios where right-turn traffic is dominant and circulating flows are moderate, offering a viable alternative to conventional intersections for improving both traffic functionality and air quality.
Provenance
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | OpenAlex-citations | — | — | 1 | 2026-06-20 |
| archive | success | unpaywall | — | — | 2 | 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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