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With the advancement of autonomous driving technology, scenario-based testing has become the mainstream testing method for intelligent vehicles. However, traditional risk indicators often fail in roundabout scenarios and cannot accurately define dangerous situations. To accurately quantify driving risks in roundabout scenarios, an improved driving safety field model is proposed in this paper. First, considering the unique traffic flow characteristics of roundabouts, the dynamic characteristics of vehicles during diverging or merging were taken into account, and the driving safety field model was improved to accurately quantify the driving risks in roundabout scenarios. Second, based on data from the rounD dataset, the model parameters were calibrated using the social force model. Finally, a DENCLUE-like method was used to extract collision systems, calculate vehicle risk degree, and analyze these risks for both the temporal and the spatial dimensions, providing guidance for virtual testing. The proposed method significantly improves detection efficiency, increasing the number of identified dangerous scenarios by 175% compared to the Time to Collision (TTC) method. Moreover, this method can more accurately quantify driving risks in roundabout scenarios and enhance the efficiency of generating dangerous scenarios, contributing to promoting the safety of autonomous vehicles. [ABSTRACT FROM AUTHOR]

The reconstruction of a standard at-grade intersection into a roundabout is very often motivated by the need to improve traffic safety, and the effects are usually monitored through before–after analyses based on traffic accidents. As in some countries, like Croatia, data on traffic accidents are not available, in this study, a methodology for the estimation of roundabout implementation effects based on measured operating speeds was developed and applied. This methodology enabled the analysis of the development of roundabouts designed according to the Croatian guidelines through the analysis of four roundabout case studies. Statistical analyses of before–after operating speed were performed, and speed time distribution variations, traffic volumes, and design elements were analyzed, compared, and correlated. Statistically significant differences were found between operating speeds before and after the reconstruction, although the expected effect of speed reduction of roundabouts was not observed. The weak correlations observed between the individual design elements of the roundabouts and operating speed highlight the need to analyze the combination of design elements with operational speed. The application of the developed methodology enabled systematic safety analyses of the selected roundabouts. The results of the analyses suggest a need to revise the guidelines. [ABSTRACT FROM AUTHOR]

Autonomous driving has witnessed rapid advancement; however, ensuring safe and efficient driving in intricate scenarios remains a critical challenge. In particular, traffic roundabouts bring a set of challenges to autonomous driving due to the unpredictable entry and exit of vehicles, susceptibility to traffic flow bottlenecks, and imperfect data in perceiving environmental information, rendering them a vital issue in the practical application of autonomous driving. To address the traffic challenges, this work focused on complex roundabouts with multi-lane and proposed a Perception EnhancedDeepDeterministic Policy Gradient (PE-DDPG) for AutonomousDriving in the Roundabouts. Specifically, themodel incorporates an enhanced variational autoencoder featuring an integrated spatial attention mechanism alongside the Deep Deterministic Policy Gradient framework, enhancing the vehicle's capability to comprehend complex roundabout environments and make decisions. Furthermore, the PE-DDPG model combines a dynamic path optimization strategy for roundabout scenarios, effectively mitigating traffic bottlenecks and augmenting throughput efficiency. Extensive experiments were conducted with the collaborative simulation platform of CARLA and SUMO, and the experimental results show that the proposed PE-DDPG outperforms the baseline methods in terms of the convergence capacity of the training process, the smoothness of driving and the traffic efficiency with diverse traffic flow patterns and penetration rates of autonomous vehicles (AVs). Generally, the proposed PE-DDPGmodel could be employed for autonomous driving in complex scenarios with imperfect data. [ABSTRACT FROM AUTHOR]

This paper presents a simulation-driven method for assessing the safety and efficiency of traffic at roundabouts incorporating connected and automated vehicle (CAV) technology. Utilizing the newly proposed CAV-based factors specified by the Highway Capacity Manual (HCM) provided a practical framework for analyzing capacity dynamics across various traffic scenarios. Using microscopic traffic simulation on a roundabout model replicating real-world geometry and traffic attributes facilitated the identification of crucial behavioral parameters. This simulation spanned from smooth traffic scenarios to operational saturation, aiding in the study of mixed traffic scenarios during the transition to increasing CAV presence. Additionally, the study assessed the safety and traffic impact of a dedicated CAV lane using surrogate safety metrics. Aimsun software aided in model parameter calibration, which, combined with the Surrogate Safety Assessment Model (SSAM), supported safety analysis. Despite observed enhancements in roundabout performance with CAV integration, the benefits of a designated CAV lane highlighted the potential to reduce conflicts among vehicles. In conclusion, the paper emphasizes the overall performance enhancement achieved with CAVs at roundabouts while also providing insights for evaluating the potential of CAV technologies in future mobility management strategies. [ABSTRACT FROM AUTHOR]

The frequency and severity of traffic accidents are causing growing concern. This study aims to develop a tool to improve the traffic safety level on roundabouts and identify the influence of traffic operations, geometric parameters, weather, and time of day on improving roundabout traffic safety. It is the first study to evaluate the performance of the integrated Median Ranked Set Sample (MRSS) and Analytic Hierarchy Process (AHP) with statistical analysis. A hierarchy tree of accident causes has been developed using data gathered from accident reports and relevant authorities. Then, the selected stakeholders’ professionals prioritized the traffic accident causes using a MRSS and AHP. Moreover, traffic microsimulation software VISSIM was also used to extract traffic operation parameters for the analysis. Afterwards, Analysis of Variance (ANOVA) was used to validate the causes of traffic accidents. The results show that geometric design accounts for 36% of accidents at roundabouts, followed by traffic operation (22%). However, conflicting and queuing lengths are responsible for about 20% of traffic accidents. The tools developed, and the causes of accidents determined in this study will help geometric designers and city planners to take the necessary measures to minimize accidents and enhance traffic safety levels in urban areas. [ABSTRACT FROM AUTHOR]

Transforming intersections into roundabouts has shown that a sufficient degree of road safety and traffic capacity can be achieved. Because of the lower speeds at the area of a roundabout, drivers tend to become more easily adaptive to any kind of conflict with the surrounding environment. Despite the contribution to safety, the design elements of roundabouts are not uniformly fixed on a worldwide scale because of different traffic volumes, vehicle dimensions, drivers' attitude, etc. The present study provides a brief overview of the contribution of roundabouts to road safety and the interactions between safety and the design elements of roundabouts. In addition, discussion points about current challenges and prospects are elaborated, including findings from the environmental assessment of roundabouts; their use and performance on the era of autonomous vehicles that will dominate in the near future; as well as the role and importance of simulation studies towards the improvement of the design and operation of roundabouts in favor of safer vehicle movement. The criticality of roundabouts, in terms of their geometric design as well as the provided road safety, lies upon the fact that roundabouts are currently used for the conventional vehicle fleet, which will be gradually replaced by new vehicle technologies. Such an action will directly impact the criteria for road network design and/or redesign, thereby continuously fostering new research initiatives. [ABSTRACT FROM AUTHOR]

With the rapid advancement of autonomous vehicles reshaping urban transportation, the importance of innovative traffic management solutions has escalated. This research addresses these challenges through the deployment of roadside units (RSUs), aimed at enhancing traffic flow and safety within the autonomous driving era. Our research, conducted in diverse road settings such as straight and traffic circle roads, delves into the RSUs' capacity to diminish traffic density and alleviate congestion. Employing vehicle-to-infrastructure communication, we can scrutinize its essential role in navigating autonomous vehicles, incorporating basic safety messages (BSMs) and probe vehicle data (PVD) to accurately monitor vehicle presence and status. This paper presupposes the connectivity of all vehicles, contemplating the integration of on-board units or on-board diagnostics in legacy vehicles to extend connectivity, albeit this aspect falls beyond the work's current ambit. Our detailed experiments on two types of roads demonstrate that vehicle behavior is significantly impacted when density reaches critical thresholds of 3.57% on straight roads and 34.41% on traffic circle roads. However, it is important to note that the identified threshold values are not absolute. In our experiments, these thresholds represent points at which the behavior of one vehicle begins to significantly impact the flow of two or more vehicles. At these levels, we propose that RSUs intervene to mitigate traffic issues by implementing measures such as prohibiting lane changes or restricting entry to traffic circles. We propose a new message set in PVD for RSUs: road balance. Using this message, RSUs can negotiate between vehicles. This approach underscores the RSUs' capability to actively manage traffic flow and prevent congestion, highlighting their critical role in maintaining optimal traffic conditions and enhancing road safety. [ABSTRACT FROM AUTHOR]

The service level is the quality of traffic conditions in the road network, which includes comfort, safety, freedom of maneuvering and so on. There are different service level depending on the conditions and circumstances of the roundabout construction. The purpose of this paper is to highlight the geometric elements as highly important parameters in the uninterrupted traffic flow in roundabouts, as well as the safety elements for an uninterrupted and efficient traffic flow. [ABSTRACT FROM AUTHOR]

Roundabouts are a common traffic infrastructure, which are supposed to facilitate safe and smooth traffic flow. Electric bikes as a common traffic tool in a lot of cities in China play an important role in relieving traffic congestion due to the rapid increase of motor vehicles on roads. However, compared with cyclists, e-bikers are more vulnerable because of their higher speed when colliding with motor vehicles. In this research, the spatial-temporal distribution characteristics of conflicts between motor vehicles and electric bikes (e-bikes) at signalized roundabouts are explored. First, the time distance method was used to identify conflicts, and the time to collision (TTC) was selected as the discrimination index we proposed for two representative conflict types. On conflict heat maps and conflict distribution during one signal cycle, we found a series of spatial-temporal conflict distribution regularities. Spatially, the proposed two representative types of conflicts were mainly distributed at exit areas and near the outermost circulatory lanes. Conflict Type 1 was mainly distributed around the outermost motor vehicle lanes, and Type 2 was mainly distributed inside the outermost vehicle lanes and behind the second stop line. In time span, both types of conflicts showed rapid increase before reaching a peak at 30 percentile green time and then decreasing gradually after that peak. Type 1 presented a sharp increasing range during 0–10 percentile green time, while the sharp increasing range for Type 2 presented during the 10–20 percentile. The conclusions developed by this article could provide a theoretical basis for improving traffic safety at roundabouts. [ABSTRACT FROM AUTHOR]

The article discusses the evolution of roundabout roads in the northeastern U.S. Topics include the strong resistance of people against the construction of modern roundabout in the northeastern region despite being life-savers, failures of roundabouts in Massachusetts, and New York State Department of Transportation's (NYSDOT's) Roundabouts First property to create roundabout corridors in 2006.

The essential of developing an advanced driving assistance system is to learn human-like decisions to enhance driving safety. When controlling a vehicle, joining roundabouts smoothly and timely is a challenging task even for human drivers. In this paper, we propose a novel imitation learning based decision making framework to provide recommendations to join roundabouts. Our proposed approach takes observations from a monocular camera mounted on vehicle as input and use deep policy networks to provide decisions when is the best timing to enter a roundabout. The domain expert guided learning framework can not only improve the decision-making but also speed up the convergence of the deep policy networks. We evaluate the proposed framework by comparing with state-of-the-art supervised learning methods, including conventional supervised learning methods, such as SVM and kNN, and deep learning based methods. The experimental results demonstrate that the imitation learning-based decision making framework, which ourperforms supervised learning methods, can be applied in driving assistance system to facilitate better decision-making when approaching roundabouts. [ABSTRACT FROM AUTHOR]

New mobility transport systems are expected to be autonomously driven. Even if public interest and a priori acceptability of such systems are high, there is only a few studies with people that already experienced an automated mobility system. This paper presents the results of a questionnaire study after experience the automated vehicle in the Tornado project. 155 users tested the vehicle in an itinerary of 6.5 km with an average speed of 25 km/h and a maximum speed of 50 km/h including straight stretches, intersections, traffic lights, roundabouts, narrow roads and a tunnel. Questionnaire content is based on some of the determinants of the unified theory of acceptance and use of technology (UTAUT) and car technology acceptance models (CTAM) together with an additional determinant introduced to analyze if vehicle performance seems natural. Usefulness, safety and enjoyment of automated vehicles already claimed in other projects are here confirmed even if speed is increased compared to previous projects. The increase in the maximum speed is not directly associated to a reduction on the safety feeling on-board. Answers have also been correlated to demographic characteristics of respondents, confirming some findings in the literature, and adding new ones related to previous autonomous vehicle experience and education level. [ABSTRACT FROM AUTHOR]

• We examined how driver support affects trust and perceived risk, and at which level of detail physiology and behaviour can identify risk perception. • Drivers held an appropriate safety attitude towards driver support. • Trust was higher in manual driving compared to when using driver support. • Physiology responds to risk events on average, but lacks reliability for detecting perceived risk in individual events. To encourage appropriate use of driving automation, we need to understand and monitor driver's trust and risk perception. We examined (1) how trust and perceived risk are affected by automation, driving conditions and experience and (2) how well perceived risk can be inferred from behaviour and physiology at three levels: over traffic conditions, aggregated risk events, and individual risk events. 30 users with and without automation experience drove a Toyota Corolla with driving support. Safety attitude, subjective ratings, behaviour and physiology were examined. Driving support encouraged a positive safety attitude and active driver involvement. It reduced latent hazards while maintaining saliently perceived risks. Drivers frequently overruled lane centring (3.1 times/minute) and kept their feet on or above the pedals using ACC (65.8% of time). They comfortably used support on curvy motorways and monotonic and congested highways but less in unstable traffic and on roundabouts. They trusted the automation 65.4%, perceived 36.0% risk, acknowledged the need to monitor and would not engage in more secondary tasks than during manual driving. Trust-in situation reduced 2.0% when using automation. It was 8.2% higher than trust-in-automation, presumably due to driver self-confidence. Driving conditions or conflicts between driver and automation did not affect trust-in-automation. At the traffic condition level, physiology showed weak and partially counter-intuitive effects. For aggregated risk events, skin conductance had the clearest response but was discernible from baseline in < 50%. Pupil dilation and heart rate only increased with strong braking and active lane departure assist. For individual risk events, a CNN classifier could not identify risk events from physiology. We conclude that GSR, heart rate and pupil dilation respond to perceived risk, but lack specificity to monitor it on individual events. [ABSTRACT FROM AUTHOR]

Connected and automated vehicles (CAVs) are expected to transform future transportation systems. Over time, these vehicles might enhance traffic efficiency and safety, especially at urban intersections. Therefore, it is essential to make adaptations to the traffic analysis models that are currently designed for human-driven vehicles only. This paper aims to assess the impact of CAVs on the entry capacity of roundabouts and develop an approach to adjust the capacity values calculated by the Highway Capacity Manual (HCM) for planning level analysis. Both single- and double-lane roundabouts are studied under various CAV market penetration rates and conflict flow rates in this paper. A specific CAVapplication, cooperative adaptive cruise control (CACC), is evaluated in this study because it enhances the car-following behavior at the roundabout entrance and has the best potential for improving the entry capacity. The simulation results indicate that the introduction of CAVs can substantially improve the entry capacity as the market penetration rate increases for both singleand double-lane roundabouts. The capacity improvement is more significant in the single-lane roundabout than in the double-lane roundabout. The capacities under different CAV market penetration rates and conflict flow rates are calculated and compared with the capacity results estimated from base models in the HCM to acquire the adjustment factors. Finally, a table of capacity adjustment factors is provided for the future implementation of HCM models. [ABSTRACT FROM AUTHOR]

The unique traffic situation at roundabouts causes complex interactions between merging vehicles, thereby increasing the likelihood of conflicts. Reliable prediction of conflict risk contributes to active safety improvement, but few studies have investigated the merge risk of roundabouts at a microscopic level. In light of this, this study develops a hybrid deep learning framework for predicting potential conflict risks in complex merging scenarios at roundabouts. Specifically, a roundabout coordinate system is devised to define vehicle characteristics based on trajectory data. Then, an improved 2D-TTC (time-to-collision) indicator is employed to identify two-dimensional merge conflicts. Since the surrounding vehicles may change as vehicles merge into a roundabout, this study analyzes several merging scenarios involving different vehicle groups and conflict durations in order to provide a comprehensive understanding of the conflict mechanism. For these scenarios, a hybrid model consisting of a convolutional neural network (CNN) and a long short-term memory network (LSTM) integrated with the convolutional block attention module (CBAM) is utilized to identify key features. The superiority of the proposed prediction method is demonstrated in comparisons with benchmark models. Results showed that segmental predictions were more accurate than overall predictions in terms of conflict duration. Furthermore, it is possible that a specific vehicle group has a decisive effect on the merging conflict risk, as indicated by the fact that information from multiple vehicle groups does not significantly improve the prediction performance. Another finding is that the driving state of vehicles merging at the roundabout varies considerably, but rarely with consecutive or multiple changes. The study provides novel insights into roundabout conflict prediction, which could serve as a tool for enhancing safety management involving complex traffic scenarios. [ABSTRACT FROM AUTHOR]

• This review synthesizes the literature on the role of traffic conflicts in roundabout safety evaluation. • Current surrogate safety indicators are not appropriate for measuring roundabout conflicts involving in three or more road users. • The configuration and geometry elements of a roundabout are related to the types and frequency of the conflicts. • The conflicts involving more than two vehicles or vulnerable road users need more studies in future research. • Traffic signs, signals and technologies of intelligent connected vehicles should be used comprehensively to control roundabout conflicts. The roundabout is one type of at-grade intersection commonly seen in many countries. The evaluation of roundabout safety is usually counted on conflict analysis of the roundabout traffic due to random and limited records of real accidents. This paper surveyed published papers and reports that investigate the role of traffic conflicts in roundabout safety evaluation. It summarized the definitions and observation methods of roundabout conflicts and classified the attributing factors of roundabout conflicts and the countermeasures to control the conflicts. This study found that although unique traffic flow movements at roundabouts create special patterns of roundabout conflicts, the methods of roundabout conflict analysis used in most existing studies were inherited from the studies of highway or cross-intersection conflicts, including conflict definitions, conflict measurements, and thresholds of conflict severity. Special or improper designs of roundabout configurations or basic geometry elements could arouse roundabout conflicts. The most common vehicle-to-vehicle conflicts were entering-circulating conflicts, sideswipe conflicts, and exiting-circulating conflicts. The conflicts among vehicles and vulnerable road users (VRUs) easily evolved into serious collisions, but these conflicts did not get deserved attention in previous studies. Drivers' familiarity with roundabouts also affected road users' safety. Traffic signs and pavement markings were commonly used to control roundabout conflicts, while traffic signals were more effective methods for the roundabouts with uneven distribution of approaching traffic or high traffic volume. Based on the analysis of existing studies, this paper pointed out seven future directions of further research in term of conflict measurement, data collection, infrastructure and access management, geometry, drivers and VRUs, signal control, and vehicle control. [ABSTRACT FROM AUTHOR]

The present work seeks to analyze how a roundabout in a metropolis in the Northeast is affected by the increase in traffic generated by the allocation of a pole that generates trips in its area. The work included a bibliographic survey on the subject and used sampling and observation in loco, following the methodology of the National Department of Transport Infrastructure - NDIT, counting the number of vehicles in the four points of the spine, as shown by noting the license plates of the vehicles that they entered and left the roundabout making a segmentation line every 15 minutes. The data were tabulated and analyzed with the aid of MS Excel ®. The results showed that if the current growth rate of 7% for the fleet is maintained, the service level during peak hours will drop sharply reaching the worst level in 2022. It has also been observed that failure to respect driving rules also causes delays and conflicts reducing traffic safety at the roundabout. The suggested proposals are the allocation of auxiliary time-saving mechanisms such as traffic lights and an educational campaign to maintain the level of service. [ABSTRACT FROM AUTHOR]

Historically, there are several large roundabouts in Vilnius with traffic organisation and safety problems. Vilnius City Administration initiated changes on these large roundabouts in 2016, by introducing new traffic organisation schemes and using relatively simple measures such as the line markings, safety measures and road signs. The aim of the research is to analyse the number of traffic accidents on the roundabouts before and after such traffic reorganisation. The article is based on accident maps in roundabouts created by the authors. Based on the comparison of accident maps, the safety trends were analysed and summarised. [ABSTRACT FROM AUTHOR]

The main objective of the work was inventory intersections like roundabouts in all cities with poviat rights located in two voivodeships of Poland: Upper Silesian and Masovian, and then performing users surveys of registered roundabouts. Survey research had two main objectives. The first one was to learn how vehicle drivers, pedestrians and cyclists perceived roundabouts as safe or unsafe road solutions. The second one was to learn about the behaviour of three users groups: vehicle drivers, pedestrians and cyclists on this type of road infrastructure in terms of traffic safety. [ABSTRACT FROM AUTHOR]

This paper is a case study, which among other things includes the analysis of the three roundabouts entry capacity: a turbo- and two spiralroundabouts. These intersections are located in one of the main road localised in Sosnowiec city (Poland). Before reconstruction, this road was characterised by unfavourable road and traffic conditions, insufficient capacity and low traffic safety level. The traffic congestion decreased significantly, traffic and road conditions, as well as the level of road traffic safety, were improved after the rebuilding of this route and the designing of three roundabouts on it. Results obtained from field measurements enabled comparative analysis of theoretical and empirical capacity values: lanes on the entry of turbo-roundabout and entries of the spiral-roundabout. This paper presents also characteristics of turbo- and spiralroundabouts with methods, which are dedicated to entry capacity calculation. [ABSTRACT FROM AUTHOR]

It is well known that a roundabout is an efficient and safe intersection. However, the safety is generally influenced by the given various conditions. This study analyzed the effects of the geometric and traffic flow conditions on traffic accident frequency at roundabouts, constructed in Korea since 2010. Many previous studies have investigated the efficiency and safety effects of roundabout installation. However, not many studies have analyzed the specific influences of individual geometric elements and traffic flow conditions of roundabouts. Accordingly, this study analyzed the effects of various influencing variables on traffic accident frequency based on a random parameter count model using traffic accident data in 199 roundabouts. Using random parameters that can take into account unobserved heterogeneity, this study tried to make up for the weakness of the fixed parameters model, which constrains estimated parameters to be fixed across all observations. A total of eight variables were determined to be the main influencing factors on traffic accident frequency including the number and width of entry lanes, the presence of pedestrian crossings, the width of the circulatory lanes, the presence of central islands, the radius and number of entry lanes, and traffic volume influence accident frequency. Based on the study results, safer roundabout design and more efficient roundabout operation are expected. [ABSTRACT FROM AUTHOR]

Double-lane roundabouts have been created in many European countries over the past few centuries and are now characterized by an unsafe geometric development and by a low sustainability capacity or level. In this regard, new double-lane geometries have been implemented to overcome to these critical points. This article shows a comparison of two nonconventional double-lane roundabout schemes defined as elliptical and turbo. Considering this research on the unsafe and congested conditions for each road schemes at grade, the microsimulation approach allows comparing schemes of intersections not yet realized in order to be able to evaluate the critical issues. A symmetric traffic distribution and an identical vehicle mix for both design solutions are considered. The research was conducted considering two different double-lane roundabout-turbo roundabout and the elliptical roundabout. By comparing their geometry and technical elements, this article assumes that turbo roundabout due to its physical separating traffic lanes in the central circulatory carriageway will enable potentially better traffic safety conditions. This article has the following main goal: a comparison of traffic safety using VISSIM microsimulator and SSAM tools. The results can provide to show safety level on investigated scenario considering level of service (LOS) and also the possibility of obtaining time to collision (TTC) and postencroachment time (PET) through the use of surrogate parameters obtained by SSAM tool. In fact, the surrogate safety parameters allows evaluating the possible collision scenarios between them, according to the trajectories of the single vehicles. This assessment is useful in order to be able to evaluate by the local authorities which of the examined schemes can provide greater negativity in the construction and operation phase. Therefore this comparative analysis allows reducing, in the preliminary phase, possible security impacts and also economic ones for the community. [ABSTRACT FROM AUTHOR]

Upgrade of the Ejisu-Kumasi section of the N6 saw the construction of roundabouts at selected intersections. Their use appears challenging particularly for vehicles with elevated Centre-of-Gravity. The objective of this study was to establish the relative risk of traffic accident deaths or hospitalized injuries at the roundabouts. Five-year crash data covering a 100 m stretch upstream and downstream of the roundabouts were analysed. A total of 119 crashes occurred with 18% casualty hospitalization and 12%fatalities. Compared with the Ejisu roundabout, fatal or hospitalized injuries were significantly higher at the Boadi (OR = 25.6, p = 0.0021) and Kwame Nkrumah University of Science and Technology Police Station Junctions (OR = 48.2, p < 0.001). Occupants of buses, heavy goods vehicles and riders of two wheelers were at elevated risk of deaths or serious injuries. Crash severity at the round abouts was aggravated by night-time, steep gradients and adverse cambers. It is recommended that, signalization and grade separation should be used in the current arrangement where appropriate. [ABSTRACT FROM AUTHOR]

A detailed analysis of traffic conditions at the intersection allows us to obtain information about the efficiency of its operation. This type of analysis usually involves assessing the capacity and scale of the intersection and applying classical measures to assess its quality. In Poland, for this purpose, methods developed by the General Directorate for National Roads and Motorways are used to estimate the capacity of intersections without traffic lights, intersections with traffic lights, and roundabouts. The paper presents the results of the analysis of traffic conditions at the intersection of Brzezinska and Nowochrzanowska Streets, located in Myslowice (Silesian Province, Poland). The paper also examines the findings on traffic safety at this intersection. [ABSTRACT FROM AUTHOR]

Turbo-roundabouts are new type of roundabouts that recently become more popular for their significant advantages. Due to their specific geometry of spiral leading circulatory lanes and raised lane dividers provide a high level of traffic safety while a relatively large capacity maintain. To compare with conventional double-lane roundabouts, turbo-roundabouts ensure above all a reduced number of conflict points moreover without waving and lower driving speed through the intersection. Challenge of this paper is to transfer existing single-lane roundabout into configuration models of basic and egg turbo-roundabouts and compare their capacity characteristics. Case study is placed in Zilina, the city on the north of Slovakia, where the single lane roundabout has a great congestion problem not just during peak hours. Configurations of the roundabout are evaluated and compared from their performance parameters using microsimulations and theoretical models. For calibration procedure of microsimulation, complex data obtained from survey of existing roundabout were used and derived as input variables for two new configurations. This example is to demonstrate the capacity increase of turbo-roundabouts comparing with single-lane roundabout and the comparison of microsimulation model and theoretical models to determine capacity of turbo-roundabouts. [ABSTRACT FROM AUTHOR]

Building safe and effective roundabouts requires optimizing traffic (operational) efficiency (TE) and traffic safety (TS) while taking into account geometric factors, traffic characteristics and local constraints. Most existing simulation-based optimization models do not simultaneously optimize all these factors. To capture the relationship among geometry, efficiency and safety, we put forward a model formulation in this paper. We present a new multi-criteria and simultaneous multi-objective optimization (MOO) model approach to optimize geometry, TE and TS of urban unsignalized single-lane roundabouts. To the best of our knowledge, this is the first model that uses the multi-criteria decision-making method known as analytic hierarchy process to evaluate and rank traffic parameters and geometric elements of urban single-lane roundabouts. The model was built based on comprehensive review of the research literature and existing roundabout simulation software, a field survey of 61 civil and traffic expert engineers in Croatia, and field studies of roundabouts in the Croatian capital city of Zagreb. We started from the basis of Kimber’s capacity model, HCM2010 serviceability model, and Maycock and Hall's accident prediction model, which we extended by adding sensitivity analysis and powerful MOO procedures of the bounded objective function method and interactive optimization. Preliminary validation of the model was achieved by identifying the optimal and most robust of three geometric alternatives (V.1-V.3) for an unsignalized single-lane roundabout in Zagreb, Croatia. The geometric parameters in variant V.1 had significantly higher values than in the existing design V.0, while approaches 1 and 3 in variant V.2 were enlarged as much as possible within allowed spatial limits and Croatian guidelines, reflecting their higher traffic demand. Sensitivity analysis indicated that variant V.2 showed the overall highest TE and TS across the entire range of traffic flow demand and pedestrian crossing flow demand at approaches. At the same time, the number of predicted traffic accidents was similar for all three variants, although it was lowest overall for V.2. The similarity in predicted accident frequency for the three variants suggests that V.2 provides the greatest safety within the predefined constraints and parameter ranges explored in our study. These preliminary results suggest that the proposed model can optimize geometry, TE and TS of urban single-lane roundabouts. [ABSTRACT FROM AUTHOR]

Although, roundabouts have proved significant in improving safety, capacity, and environmental performance, they have shown an increasing crash rate in Oman over the years. This article aims to evaluate the safety performance of the roundabouts in Oman through the development of crash-prediction models to examine the relationship between the geometric, traffic flow variables, and crash frequency and severity. These models can determine which variables are the best indicators for safety performance. GLM technique with Poisson or negative binomial regression (NBR) was carried out to develop these models. Two types of models were developed separately: the flow-based models including only exposure functions, and the full models containing exposure functions and other significant geometry and traffic variables. The result shows that the 85th percentile speed, number of lanes at specific approach, entry angle, and circulating width were the most significant variables. It was found that reducing the 85th percentile speed reduces the total and injuries crashes, however increasing the number of lanes in each approach and adding right-turn bypass lane may be the most effective methods to reduce the rear-end accidents. [ABSTRACT FROM PUBLISHER]

Correctly designed roundabouts proved to have positive safety and functional performances. However, they are also affected by peculiar disadvantages. In particular, they are difficult to manoeuvre, especially for heavy vehicle drivers. Despite these concerns, there are currently no driving workload metrics devoted to roundabouts. A novel methodological approach is proposed for trying to quantify workload impinging on heavy vehicle drivers when manoeuvring through complex at-grade intersections. Proper acquisition of input data constitutes the starting point for future research about ascertainment of workload for these particular road scenarios. The described procedure enables recording steering wheel angles performed by a driver when manoeuvring an articulated lorry through a complex at-grade intersection. A field trial was carried out for verifying the practical feasibility of proposed method in capturing driver’s steering behaviour. Dynamic data acquired via global navigation satellite system instrumentation were related to actual driver’s steering wheel behaviour captured by camera frames. As a complement to the experiment, selected steering behaviour metrics were calculated. Steering Entropy attributed a high difficulty level to the manoeuvres performed through the roundabout, whereas High Frequency Component and Steering Reversal Rate showed intensity and occurrences of driver’s corrections needed for controlling position of the semitrailer at the ring. It appears that even a single roundabout may represent an arduous task for drivers. The study concludes with recommendations for further research about workload imposed by roundabouts to heavy vehicle drivers, with special attention to successions of closely spaced roundabouts. [ABSTRACT FROM AUTHOR]

This paper presents a meta-analysis of the road safety effects of converting junctions to roundabouts. 44 studies containing a total of 154 estimates of effect were included. Based on a meta-regression analysis, converting junctions to roundabouts is associated with a reduction of fatal accidents of about 65% and a reduction of injury accidents of about 40%. The mean effect on property-damage-only accidents is ambiguous. Summary estimates of effect are robust for fatal and injury accidents, but vary depending on the model of meta-analysis and the treatment of outlying data points for property-damage-only accidents. A trim-and-fill analysis suggests a weak tendency for publication bias, with modest influence on summary estimates of effect. It is concluded that roundabouts are very effective in reducing traffic fatalities. [ABSTRACT FROM AUTHOR]

The use of roundabouts is gaining popularity in North America for their safety, capacity, and environmental benefits. Studies have shown that roundabouts can significantly reduce injury collisions compared to stop control and traffic signals. As more roundabouts are constructed, there will be an increased need for a detailed analysis of their safety performance. Traditional road-safety analysis of roundabouts has relied on the use of historical collision records. This approach offers a less-complete understanding of roundabouts safety and their effects on the behavior of drivers, pedestrians, and cyclists. This paper represents a case study where automated video-based traffic conflicts analysis is used to diagnose safety issues at a roundabout in Vancouver, British Columbia, Canada. Traffic conflicts are automatically identified and analyzed to develop an in-depth understanding of the behavior of road users and the causes of traffic conflicts. Conflicts contributing factors were identified and safety countermeasures are presented. [ABSTRACT FROM AUTHOR]

Roundabouts around the world are often seen as a beneficial measure for intersection safety. Although their number has grown recently in the Czech Republic, their safety impact has not been fully studied. Furthermore, Czech roundabouts have sometimes been unpopular, including doubts about their benefits. This situation inspired the authors to investigate three questions related to Czech roundabouts: (1) Are roundabouts safer than traditional intersections?; (2) Are roundabout conversions beneficial for safety?; (3) Is Czech roundabout safety performance comparable to other countries? Safety performance functions were developed based on data samples and used in order to answer these research questions. The final results are mixed: roundabouts seem to be safer compared to traditional intersections and before-after study of urban roundabout conversions yielded positive crash modification factors; on the other hand, expected crash frequencies on Czech roundabouts are higher compared to other European countries. [ABSTRACT FROM AUTHOR]

This article presents an approach for studying different aspects of traffic safety at roundabouts. An automated safety analysis framework is used to detect different types of traffic conflicts, as well as the inappropriate negotiations and the gap acceptance behavior of drivers. To test the validity of the proposed method, a case study is used for a roundabout in Doha, Qatar. Seven types of traffic conflicts are studied and their severity is identified using the time-to-collision conflict indicator. Four common types of driver inappropriate negotiations behavior are also investigated. The analysis shows that most of the inappropriate negotiations and traffic conflicts are due to drivers' poor lane discipline that can be partially attributed to the poor lane marking. Gap acceptance behavior is also studied by identifying lead, lag, and total gaps. The traffic conflicts, inappropriate negotiations, and gap acceptance results are validated by a comparison with manual observations. The results of the validation process show the viability of the automated approach that produces acceptable results with less time and effort. Moreover, the data collected using this approach provides further insights on roundabout safety evaluation and has the potential for use in the assessment of roundabout design. [ABSTRACT FROM AUTHOR]

Drivers may modulate their secondary behavior based on roadway or driving demand, but there is little research capturing secondary behaviors in a range of driving situations among a large sample of drivers on actual roadways. Weekday daytime and nighttime roadside observations were conducted of drivers traveling in free-flowing traffic on a straightaway, in a roundabout, and when moving or stopped at a signalized intersection on the same roadway in four Northern Virginia communities. The presence of 12 secondary behaviors were noted for each of the 16,556 drivers observed. Overall, 23% of drivers observed were engaged in some kind of secondary behavior. The most common secondary behaviors were holding (5.1%) or talking on (4.2%) a hand-held cellphone, eating or drinking (3.1%), and talking or singing with a passenger (2.7%). Based on logistic regression analysis, the prevalence of any kind of secondary behavior and of more manually demanding behaviors, like manipulating a hand-held cellphone and eating or drinking, was highest among drivers stopped at red lights and lowest among drivers in roundabouts. Other factors also influenced the prevalence of driver secondary behavior. Drivers were more likely to be eating or drinking and less likely to be talking on a handheld phone in the morning than at others time of the day. Drivers estimated to be 60 and older were least likely to be engaged in any secondary behavior, but drivers younger than 20 and drivers 20–59 years old were equally likely. Drivers with and without passengers were equally likely to be engaged in any secondary behavior, but drivers with passengers were most likely to be talking or singing with the passengers, whereas drivers without passengers were most likely to be eating or drinking or holding, talking on, or manipulating hand-held phones. The current findings in combination with past research suggest that drivers may engage in secondary behaviors when perceived driving demand is reduced, and that roadway demand and contextual variables are important factors to consider when studying driver secondary behavior. [ABSTRACT FROM AUTHOR]

The rollover propensity of SUVs and trucks has long been recognized as a potential safety issue. The propensity may increase with the growing number of roundabouts that are being built on high-speed roadways designed for 50 mi/h or higher. This paper presents a research methodology developed to evaluate the rollover propensity of trucks on existing roundabouts and other roads with tight curves and high-speed traffic. The research objective was accomplished by developing an advanced 3D model of rollover that is applicable to field observations of the undisturbed behavior of multiple vehicles. This model was supplemented with a nonintrusive method of data collection based on recording video from a remote location and a novel method of extracting the data from the video material and processing it to generate the input required by the rollover model. The method is demonstrated in this paper on an example roundabout by evaluating the rollover propensity of semi-trailers in daytime and nighttime conditions. The results indicate that the drivers observed in nighttime conditions compensated well for the challenging conditions by driving more cautiously, which led to their rollover propensity at night being lower than during the day. The method was found useful for timely detection of the potential rollover problem without waiting for crashes. [ABSTRACT FROM AUTHOR]

The turbo roundabout is an innovative design of the two lane roundabout that has revolutionised roundabout design. According to the international research, it is determined that the turbo roundabout has a higher level of traffic safety because of the lower number of conflicts and the use of raised lane dividers. In addition, compared with the conventional two lane roundabout, turbo roundabout has higher capacity. Due to these advantages, the reconstruction of intersections into turbo roundabouts has become a kind of global trend nowadays. The first turbo roundabout in the Republic of Macedonia was designed in Skopje in 2011, without tracking the performances. This was exactly the motive to investigate the performances of this type of intersections. In this research three intersections in sequence located in Ohrid (two signalized and one non-signalized intersection) and the performances are determined for the current situation and the situation with increased flows by using the software tool SIDRA. A reconstruction of the intersections has been made into turbo roundabouts. The performances for two different cases (current situation and the situation with increased flows, with and without the pedestrians' influence) are determined with the use of both VISSIM and analytical model by Brilon&Wu. The analysis has proven that with the input parameters, turbo roundabouts offer better performances compared to the existing intersections. Thus, the reconstruction of the intersections is justified. [ABSTRACT FROM AUTHOR]

Intersection regions widely exist in road networks as crucial connections, and the congestion effects on traffic in the networks cannot be ignored. In general, a conventional intersection region includes a merging region and more than two ramps, whose congestion brings a serious negative effect on traffic service quality and satisfaction of drivers. Specifically, intersection region congestion is caused by congestion in merging regions. However, current control methods regarding coordination of the variable speed limits and ramp metering in order to solve merging region congestion are insufficient to handle congestion occurring in the intersection region. Therefore, a new method of coordinated control is proposed in this paper based on mainline control using the variable speed limits and coordinated ramp metering. The coordinated control method is formulated considering the degree of crowdedness indexes and implemented based on the queue length, with the goal to relieve congestion in conventional intersection regions caused by merging region congestion. The coordinated control method is further evaluated based on an actual traffic network. The results show that the proposed method is effective in terms of improving traffic service quality and relieving intersection region congestion. [ABSTRACT FROM AUTHOR]