A Methodological Framework to Assess Road Infrastructure Safety and Performance Efficiency in the Transition toward Cooperative Driving

Abstract

There is increasing interest in connected and automated vehicles (CAVs), since their implementation will transform the nature of transportation and promote social and economic change. Transition toward cooperative driving still requires the understanding of some key questions to assess the performances of CAVs and human-driven vehicles on roundabouts and to properly balance road safety and traffic efficiency requirements. In this view, this paper proposes a simulation-based methodological framework aiming to assess the presence of increasing proportions of CAVs on roundabouts operating at a high-capacity utilization level. A roundabout was identified in Palermo City, Italy, and built in Aimsun (version 20) to describe the stepwise methodology. The CAV-based curves of capacity by entry mechanism were developed and then used as target capacities. To calibrate the model parameters, the capacity curves were compared with the capacity data simulated by Aimsun. The impact on the safety and performance efficiency of a lane dedicated to CAVs was also examined using surrogate measures of safety. The paper ends with highlighting a general improvement with CAVs on roundabouts, and with providing some insights to assess the advantages of the automated and connected driving technologies in transitioning to smarter mobility.

Insights into Simulated Smart Mobility on Roundabouts: Achievements, Lessons Learned, and Steps Ahead

“…Assumptions regarding assertive behavior led to an operational efficiency advantage at the expense of road safety, as indicated by the frequency of conflicts identified in the simulations, especially for the two-lane roundabout (R2). Based on the findings concerning the two-lane roundabout, dedicated lanes for CAVs with turbo-like configurations, featuring a spiraling layout and curbs for separating vehicular movements, may offer greater adaptability in implementing the V2X features typical of smart infrastructure [13,80]. Additionally, cautious CAV behavior should also be simulated in order to identify the most appropriate behavioral trade-off, especially in mixed traffic.…”

“…Calibration methods, as discussed by various studies, should ensure accurate predictions [75,76]. A concise overview of select peer-reviewed studies from 2019 to 2023, primarily using PTV Vissim [77] and Aimsun [78], is provided in Table 4 [76,[79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98]. However, research on roundabouts has significantly expanded, reflecting the increasing interest in integrating smart features for enhanced functionality [11].…”

“…Stability was observed within speeds of 10 to 74 km/h, with a critical zone beyond. Nonetheless, the anticipated safety advantages of cooperative driving, compared to traditional systems, seemed to diminish in scenarios exclusively involving CAVs at roundabouts [80]. This decline was largely attributed to assumptions of assertive driving behavior in simulations, which could potentially decrease the safety margin among CAVs.…”

“…They allow engineers to assess CAV impact on traffic, congestion, road safety, and other critical transportation parameters. Microsimulation also remains crucial in transitioning scenarios incorporating cooperative vehicles and communication technology systems (e.g., [76,80,84]). Despite calibration needs, driving simulation technology offers clear advantages over real-scale measurements in evaluating safety, operational performance, and driving behavior [57,75,82].…”

Connected Automated and Human-Driven Vehicle Mixed Traffic in Urban Freeway Interchanges: Safety Analysis and Design Assumptions

“…Setting the minimum values for TTC at 0.3 s and PET at 0.50 s was necessary to address processing errors, as zero values were identified and removed [18,41]. The conflict type parameter allowed classification of conflicts based on the conflict angle, representing the hypothetical collision between the trajectories of conflicting vehicles: a rear-end conflict occurs if the absolute value of the conflict angle is less than 30 degrees and a crossing conflict occurs when the absolute value of the conflict angle exceeds 80 degrees, otherwise a lane-changing conflict occurs [42]. To clarify, a rear-end conflict occurs when two vehicles are in the same lane simultaneously, whereas lane changing involves two vehicles that have switched lanes.…”