Cyclists at Roundabouts: Risk Analysis and Rational Criteria for Choosing Safer Layouts

Cantisani, Giuseppe; Durastanti, Claudio; Moretti, Laura · 2021 · DOAJ

DOI: 10.3390/infrastructures6030034

archive: archived pipeline: cataloged verified

Get this paper ↗ (DOI — opens at the source; we link to it, we don't host it)

Summary

This study addresses the critical issue of cyclist safety at urban intersections, where over 70% of bicycle-related crashes occur. Specifically, it focuses on single-lane conventional roundabouts, aiming to quantify the risk of collisions between motor vehicles and bicycles and to identify geometric layouts that minimize this risk. The research is motivated by the need to support cycling as a sustainable transport mode while mitigating the vulnerability of unprotected cyclists in shared roadway environments. The methodology combines a probabilistic model with a damage model to assess collision risk at the eight conflict points (four merging and four diverging) of a symmetrical four-arm roundabout. The probabilistic component utilizes Poisson’s law to calculate the likelihood of simultaneous presence of vehicles and bicycles within a one-second exposure unit, based on traffic flow intensities. The damage model incorporates user reaction times and geometric constraints to classify danger levels. The study analyzes a standard layout where cyclists and vehicles share the circulatory roadway, comparing it against alternative configurations, including a "roundabike" layout featuring separated cycle paths. Input data includes specific geometric parameters (e.g., 23 m inscribed circle radius) and constant speeds (10 km/h for cyclists, 30 km/h for vehicles), assuming users adhere to traffic rules. The results demonstrate that the "roundabike" layout significantly reduces collision risk compared to the standard integrated layout where cyclists and motor vehicles share the same roadway. By physically separating bicycle traffic from motor vehicle traffic, the proposed layout effectively mitigates the exposure to conflict points. The analysis provides a quantitative basis for comparing different geometric and functional configurations under varying traffic volumes and bicycle flow rates. The significance of this work lies in providing road managers and urban planners with rational, evidence-based criteria for selecting safer roundabout designs. The findings suggest that implementing separated cycle facilities is a highly effective mitigation strategy for enhancing cyclist safety. This approach allows for the optimization of intersection geometry to balance functional traffic requirements with the safety of vulnerable road users, contributing to broader goals of reducing urban traffic congestion and improving air quality through increased cycling mobility.

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed.

Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• cyclist safety
• intersection design