A growing number of studies, presented in scientific and professional literature, point out a poor traffic safety characteristic of "standard" two-lane roundabouts, and lower capacity than expected. ...These problems are resolved in different ways in different countries; however, the most successful solution has proven to be reducing the number of conflict points. Lower number of conflict points is one of the characteristics of alternative (or unconventional or no-widespread) types of roundabouts. Alternative types of roundabout differ from "standard" two-lane roundabouts in one (or more) design elements, while the purpose of their implementation is also specific. This paper illustrates two established alternative types of roundabouts (turbo and flower roundabout), and two alternative types of roundabouts in development phase (reduced-turbo and semi-turbo roundabout), offering their detailed functional description, and comparison of their capacity and traffic safety characteristics. Comparative analyses of turbo, reduced-turbo, flower and semi-turbo roundabouts was made by evaluation approach based on simulation of traffic operating at four types of alternative design layouts, including exact geometric layout of the traffic site and the precise representation of traffic flows, with turning movements, through origin-destination matrixes. The capacity comparison was conducted by a software tool VISSIM, while the traffic safety comparison was made by a software tool SSAM. In traffic safety analyses, microsimulation was used to simulate traffic operations at various levels of traffic volume. Performance measures were obtained, including measures of traffic safety, based on conflicts estimated from trajectories generated in microsimulation. According to the results, level of traffic safety (as well as capacity) of analysed alternative types of roundabouts depends on traffic flow strength, and on numbers of right-hand and left-hand turning vehicles. Consequently, for different circumstances, there are different optimal alternative types of roundabouts.
This study aimed to investigate the effect of geometric characteristics and traffic scenarios on the performance measures, including delay, volume to capacity (v/c) ratio, capacity, and the level of ...service (LOS) in basic and rotor turbo roundabouts. In addition, it attempted to compare turbo roundabouts using performance measures based on geometric characteristics and traffic scenarios. The results showed that performance measures reduced significantly by increasing the diameter of four-leg turbo roundabouts although they improved in three-leg turbo roundabouts. Further, four- and three-leg basic turbo roundabouts had a better performance by changing the balanced to imbalanced traffic flow scenario compared with four- and three-leg rotor turbo roundabouts. Additionally, substituting four- and three-leg basic turbo roundabouts for rotor four- and three-leg turbo roundabouts increased the performance measures. Overall, the basic turbo roundabouts had a better performance compared to the rotor turbo roundabout under unsaturated and saturated traffic conditions .
Turbo-roundabouts are one of the most frequently recommended road junction design options when it comes to increasing traffic capacity and traffic safety. This is in particular true of suburban ...areas, with dominant traffic flow on the main road and moderate traffic flow on the side road. Other intersections handling local traffic and considerably constricting the availability of space are usually located in the vicinity of such intersections. Another factor contributing to the limited availability of land for construction in these locations is the presence of surrounding residential housing. Then, choosing the suitable turbo-roundabout type becomes the main issue. The article presents a case study for the selection of a type of turbo roundabout under the conditions of considerably constricted land availability based on the analysis of the provision of a swept path for the chosen design vehicles. The article considers the standard egg-type turbo-roundabouts, “look-a-like” type turbo-roundabouts, non-standard “flattened” turbo-roundabouts and ellipse-based roundabouts, with non-standard geometries of the truck apron and central island. For each of the analysed roundabout types, setting-out methods were described in detail, allowing the designer to quickly select a type of roundabout suitable for the specific constrained site conditions. This article analyses the applicability of non-standard turbo roundabouts for three area types: LUDA low urbanisation degree area, BA built-up area and CDA highly commercially developed area along the side road, wherever standard roundabouts are not practicable due to constraints imposed by existing buildings, canals or any other obstacles found at the project site.
•Government interventions is needed to implement applicable and sustainable road designs in road intersections.•Turbo-roundabout is significance in reducing traffic related accidents and ensuring ...pedestrian safety.•Triggering stop and go in roundabouts can lead to higher fuel consumptions for motorists and harmful greenhouse gas emissions for environmental sustainability.
The public transportation system is significant in increasing the efficiency of urban mobility in metropolitan cities, especially when transportation infrastructures are involved. The primary problems related to urban mobility are traffic accidents, traffic congestion, and environmental pollution from vehicles' exhaust pipes. Several types of interventions can be proposed to curb these issues; they are an application of efficient public transportation systems and the implementation of unconventional road intersections. This research focused on the adverse effects of environmental pollution and traffic safety in Bus Rapid Transit operation in a turbo roundabout. We used simulation software such as VISSIM and VERSIT + micro through EnViVer to analyze these adverse effects. The outputs gotten from EnViVer were compared to COPERT 5 mesoscopic model. The results show that the input and output are well correlated. The results also show a difference in emissions between the presence and absence of bus rapid transit (BRT) in turbo roundabout. This study contributes to the growing area of turbo roundabout research, especially for Bus Rapid Transit. Furthermore, this research will assist transportation researchers and urban planners in planning constructive transportation planning when it comes to roundabouts and road intersections.
The growing need for sustainable mobility has led the transport policy-makers as well as population to use more of soft mobility solutions such as pedestrian and cycling traffic. Several European ...countries are implementing policies for total mobility with less motorization in order to reduce the negative environmental effects generated by industries and transport. In the same time new unconventional types of intersections are developed in order to ensure safer conditions not only for motorized traffic but also for pedestrians and cyclist. One of those is turbo roundabout, at-grade two-lane roundabout, introduced also in urban areas where heterogeneous traffic users are expected and on which traffic safety should be considered carefully. This article aims to analyze the safety of cyclists in different traffic conditions at turbo roundabout with and without separated traffic lanes for cyclists. Through the evaluation of level of service and surrogate safety parameters, the advantages and critical aspects linked to turbo roundabout are highlighted. The research will be conducted on theoretical turbo roundabout with substantial variation in traffic flow. Comparison of the results will allow a better understanding of functionality (level of service, traffic safety) of turbo roundabout in the presence of pedestrians and cyclists of different age. The aim of this article is to present possible solutions to enable safer introduction of cycling traffic at turbo-roundabouts and help defining conditions (number of vehicles, number of cyclist, and number of pedestrians) in which safety of cyclist is questionable and there is need for different solution.
The paper focuses on the use of non-conventional roundabouts, such as turbo-roundabouts and flower-roundabouts, for the reduction of both functional and safety critical issues. The aim is to evaluate ...the effectiveness of non-conventional design schemes compared to conventional solutions through the implementation of vehicular traffic microsimulation techniques and swept path analysis. The work proposes two case studies in suburban areas characterized by the presence of road intersections affected by high traffic criticality. The study compares the performance in terms of average speed, queues length, time loss, vehicle manoeuvring size, etc., between the actual state and two design solutions, respectively conventional and non-conventional. The results obtained highlight the effectiveness of the non-conventional schemes adopted for both the improvement of traffic and safety parameters and for the containment of polluting emissions into the atmosphere. The work also proposes a methodological approach that can be pursued by the road designer, for the choice between alternative design solutions of conventional and non-conventional roundabout intersections.
Safety and Operational Performance of Roundabouts Tey, Li-Sian; Salim, M. S.; Shah, Shahreena Melati Rhasbudin ...
International journal of engineering and advanced technology,
11/2019, Letnik:
8, Številka:
6s3
Journal Article
Odprti dostop
When there are two or more roads meet, there is higher tendency of conflicts among vehicles. Roundabout is not a new concept to manage conflict points at at-grade intersection. However, improper ...motorist behaviours especially during peak hour affect safety and operational performance of a roundabout. This paper compares the safety and operational performance evaluation of a conventional non-signalized roundabout and a conventional signalised roundabout and explores the potential of turbo roundabout to replace the conventional ones. Three characteristics used to evaluate safety performance of the roundabouts include entry lane selection, use of entry and exit indicators, and weaving activities. These behaviours create the possibility of conflict, hence, risk of fatalities. On the other hand, delay and total time travel are used as indicators of operational performance of the roundabouts. We used SIDRA INTERSECTION Software to determine the theoretical delays and Level of Services. High delay, a time factor, affects motorists’ emotion, might have contributed to the safety performance. Similarly, motorists’ non-compliance behaviours affected the operational performance.
The construction of cities and economic development lead to more and more serious environmental pollution, and the concept of green and low-carbon city has been proposed. Therefore, a series of ...requirements have been put forward for transportation. CO and other pollutants will be produced in the exhaust of conventional fuel vehicles, which will seriously affect the urban environment, especially at intersections with large passenger and vehicle flows. When multiple roads, especially more than 4 roads, intersect on urban roads, traffic organization can usually be achieved by using a roundabout. However, due to the limited capacity of the conventional roundabout, with the rapid increase of the traffic volume, and there are many vehicles in the circle lane change and interweaving behavior. This has caused serious congestion at the roundabout, the significantly increase in pollutants emissions and the decline in air quality. As an unconventional design, the turbo roundabouts use canalized traffic to allowed drivers to select the appropriate lanes in advance depending on their destinations so that different lanes within the circle do not interfere with one another, which improves the safety of the intersection while ensuring capacity. The main purpose of this paper is to analyze the traffic efficiency and safety of the conventional roundabout scheme and turbo roundabout scheme for five-way intersections. Using VISSIM to simulate different forms of roundabout and analyzing the six selected evaluation indicators. The number of vehicles in different entrance lanes and the diameter of the circle are selected as sensitivity factors for sensitivity analysis. Finally, the factor analysis method (FAM) is used to classify the six indicators into two categories: traffic efficiency and traffic safety, so as to comprehensively evaluate the different schemes. The results show that the difference in performance between the two schemes was not significant at low traffic volumes. At high traffic volumes, the turbo roundabout was better than the conventional roundabout in terms of emissions, safety and throughput efficiency. CO emissions from vehicles on conventional roundabout are generally higher than those on turbo roundabout, up to 53.62%. Therefore, the turbo roundabout is more appropriate for heavy traffic conditions.
Spirally arranged and physically separated traffic lanes in the circulatory carriageway of turbo-roundabouts force drivers to choose a particular entry lane and, subsequently, a circulatory traffic ...lane according to their intended destination. This specificity is taken into account in theoretical capacity models for two-lane turbo-roundabout entries typically evaluated by the lane-by-lane approach. Nevertheless, this specific path of movements is not considered in the most widely used capacity models for single-lane minor entries at oval turbo-roundabouts. In these models, only one entering traffic flow conflicted by two circulating traffic flows in front of the entry is considered. However, the entering traffic flow presents a mixed traffic flow of two movements (right-turning movement and left-turning and through movement) with different capacities due to different number of conflicting traffic streams and traffic volumes allocated into the outer and the inner circulatory lane. This fact is included in the capacity estimation for a single-lane minor entry presented in the article using the existing capacity formula for the mixed traffic flow on a shared minor lane at unsignalized intersections. The entry capacity reflects the proportion of the right-turning movement within a shared entry lane as well as the specific allocation of circulating traffic flow into the outer and the inner circulatory lane. This entry capacity is about 10 % to 30 % higher compared to a single-lane entry capacity estimated according to commonly used models described in the article. Higher entry capacity in a higher proportion of the right-turning traffic within mixed entry traffic flow is confirmed also by the results of average delays estimated by the theoretical delay model and microsimulation.
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