The attention to the most vulnerable road users has grown rapidly in recent decades. The experience gained reveals an important number of cyclist fatalities due to road crashes; most of which occur at intersections. In this study, dispersion of trajectories in urban intersections has been considered to identify the whole conflict area and the largest conflict areas between cars and bicycles, and the speeds have been used to calculate exposure time of cyclists and reaction time available to drivers to avoid collision. These data allow the summary approach to the problem, while a risk probability model has been developed to adopt an elementary approach analysis. A quantitative damage model has been proposed to classify each conflict point, and a probabilistic approach has been defined to consider the traffic volume and the elementary unit of exposure. The combination of damage and probability, permitted to assess the risk of crash, at the examined intersection. Three types of urban four-arm intersection, with and without bike paths, were considered. For each scheme, the authors assessed the risk of collision between the cyclist and the vehicle. The obtained results allowed the identification of the most hazardous maneuvers and highlighted that geometry and kinematics of traffic movements cannot be overlooked, when designing an urban road intersection. The strategy proposed by the authors could have a significant impact on the risk management of urban intersections. The obtained results and the proposed hazard estimation methodology could be used to design safer intersections.
The road safety of vulnerable users is a current issue; in densely populated areas, the use of alternative and light mobility vehicles is growing in popularity, and their users conflict with vehicles having larger dimensions and masses. This study focuses on the risk analysis of collision between bicyclists and motorized vehicles in urban intersections. Twenty-five urban four-leg intersections, with and without bike paths, were considered in order to identify the conflict points, calculate their hazardousness, and assess the risk of collision using a probabilistic approach. Traffic light setup, yield line retraction, design of areas, and counter-clockwise circulation reserved for bicyclists are the geometrical and functional approaches proposed to mitigate the risk of collision. Two risk-based approaches proposed by the authors were implemented—the first examines all identified conflict points, while the second assesses the risk condition of the overall intersection. The obtained results show that the number of conflict points varied between 32 and 112 and the risk of collision varied between 4.57 × 10−2 and 2.46 × 10−1. The proposed assessment allowed us to make an objective comparison between the possible layouts for various traffic mixes and design conditions, and to identify the most effective solutions. Significant differences in terms of risk were found. Each mitigation strategy should be motivated by a reasoned decision considering the different needs of all road users, traffic demand, and geometrical and functional constraints.
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