CYCLING AT INTERSECTIONS: A MULTI-OBJECTIVE ASSESSMENT FOR TRAFFIC, EMISSIONS AND SAFETY

Bahmankhah, Behnam; Fernandes, Paulo; Coelho, Margarida C. · 2019 · Crossref

DOI: 10.3846/transport.2019.8946

archive: archived pipeline: cataloged verified

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Summary

This study addresses the integrated assessment of traffic performance, pollutant emissions, and safety at signalized intersections with increasing bicycle demand. Motivated by rising cycling rates and the high proportion of cyclist injuries and fatalities occurring at intersections, the research aims to evaluate the impacts of bicycle volume increases and alternative traffic control treatments. Specifically, it seeks to identify optimal bicycle demands that balance traffic efficiency, environmental impact, and safety, addressing a gap in literature regarding the simultaneous analysis of these factors. The methodology employs a microscopic traffic simulation model (VISSIM) coupled with a Vehicle Specific Power (VSP) emission model and the Surrogate Safety Assessment Methodology (SSAM). Data were collected from a three-leg signalized intersection in Aveiro, Portugal, including traffic volumes, vehicle dynamics via GPS-equipped vehicles, and conflict observations from video recordings. Two scenarios were analyzed: (1) increasing bicycle demand from 9 to 270 bicycles per hour (bph) while replacing motor vehicles in the existing signalized layout, and (2) replacing the signalized intersection with a two-lane roundabout and evaluating the same bicycle demand increments. The fast Non-Dominated Sorting Genetic Algorithm (NSGA-II) was used for multi-objective optimization to determine optimal bicycle demands based on trade-offs between emissions (CO2, CO, NOx, HC) and safety indicators (Time-To-Collision, maximum speed). Results indicate that increasing bicycle demand in the signalized scenario reduced vehicular emissions (average decreases of 9% for CO2, 6% for CO, 6% for NOx, and 8% for HC) but increased vehicle travel time by approximately 5% and significantly increased bicycle stops and travel time. The roundabout layout outperformed the signalized intersection, particularly at high bicycle demands. In the maximum demand scenario (270 bph), the roundabout reduced vehicle stops by 78% and travel time by 14%, while decreasing CO2, NOx, and HC emissions by 9%, 7%, and 12%, respectively. Although the roundabout reduced the total number of conflicts by 49%, it resulted in more severe conflicts and potential crashes compared to the signalized layout. Multi-objective analysis identified bicycle demands of 75, 95, and 110 bph as delivering optimal environmental and safety outcomes for the intersection. The significance of this study lies in its comprehensive, multi-objective approach to intersection design, demonstrating that roundabouts can offer superior traffic and environmental performance even with high bicycle volumes, despite potential increases in conflict severity. The findings provide actionable insights for urban planners, suggesting specific bicycle demand thresholds that optimize the balance between safety, emissions, and traffic flow. This contributes to the broader field of sustainable urban mobility by offering evidence-based strategies for integrating cycling infrastructure into existing road networks.

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Topics

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• intersection design
• cyclist safety