Roundabouts for safer roads DE WINNE, E
Transactions on the built environment,
2009, 20090101, Volume:
108
Conference Proceeding, Journal Article
Open access
This paper describes guidelines and research results about the design of roundabouts and their effects on traffic safety. After an introduction, the principal geometric elements of a roundabout are ...discussed in relation to traffic safety. Attention is given to specific accommodation for cyclists and pedestrians. Next, international research results concerning roundabouts and effects on traffic safety are discussed. Some methodological aspects as well as conclusions from research are dealt with. It is explained why roundabouts have positive effects on traffic safety. Finally, the research results are described, as well as the global effects of roundabouts on traffic safety and specific results for bicyclists and pedestrians. Some case studies, and particular roundabout designs, such as the \“turboroundabout” or the oval-roundabout, are treated and the relationship between design elements and traffic safety was explored, together with conclusions and suggestions.
The article deals with an operation issues and traffic evaluation at selected turbo-roundabouts realized in Czech Republic. Also describes redevelopment possibility of existing roundabouts with ...classic layout to the roundabouts with spiral arrangement of the traffic lanes on the circulatory roadway. Described are advantages and disadvantages of the spiral arrangement in compare with normal roundabouts. The article evaluates Czech methodology of turbo - roundabout design, which was published in 2015 and compares its findings with foreign methodologies, especially Dutch and Slovakian standards. Presented are basic divisions of turbo - roundabouts and how the single types of layout are different from the point of view of number of traffic lanes and estimated capacity. There is shown the list of realized turbo - roundabouts on which is made a comparison of identity of the selected parameters of geometric elements defined in the Czech methodology with the foreign standards. Evaluation criteria of realized constructions are basic design elements of turbo-roundabouts, traffic lane (roadway) width and layout and design arrangement with aiming on problematic design features.
The article also briefly deals with the evaluation of effectiveness from the point of view of capacity and traffic accidents, when are compared traffic accidents data at selected locations in Czech Republic where redevelopment of conventional types of intersections to turbo-roundabouts were made.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A criterion for estimating the capacity under partial and fully automated vehicles environments is presented.•A control area was hypothesized where CAVs start to communicate with a turbo roundabout ...manager system.•Different traffic scenarios were analysed in the research.•With the increase in market penetration levels of CAVs, entry capacities increase accordingly.
This article presents a methodology to estimate the entry capacity (EC) and total capacity (TC) of basic turbo roundabouts under partial and fully connected and autonomous vehicle (CAV) environments. EC calculations are partially based on capacity models and adjustment factors proposed by the HCM 7th edition, taking into account different proportions of CAVs in traffic streams. The proposed methodology was applied to a case study concerning a basic turbo roundabout with different traffic demands and market penetration levels (MPLs) of CAVs. It was assumed that the traffic stream consisted of 100% passenger cars with MPLs of CAVs ranging from 0% to 100%. The research proves that with the increase in MPLs of CAVs, ECs increase accordingly and delays and queues decrease. To maximize the TC, a control area was also hypothesized, where CAVs start to communicate with a turbo roundabout manager system. The system should be able to distribute and channel CAVs, and therefore the entering flows between entry lanes find the values of the maneuver distribution factors (α, β, γ, δ) between the right lane and the left lane of entries to maximize the TC for each origin–destination matrix of traffic flows.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
There are to two groups of turbo roundabouts used currently in Poland. The first group is turbo roundabouts with geometry and traffic organization designed following the model of Dutch turbo ...roundabouts with raised lane dividers. The other group is turbo roundabouts with traffic organization which entirely or partly corresponds to traffic organization of conventional turbo roundabouts, but with lane dividers not present, with their function performed by a single continuous line of P-2 type. Turbo roundabouts in the world are considered as solutions which are characterized by a high level of road safety and allow for effective flow at substantial traffic intensities. The data about turbo roundabouts in Poland analysed by the author show that there are substantially more turbo roundabouts without raised lane dividers. The paper attempts to answer to the question of whether turbo roundabouts with lane dividers in the form of a single continuous line ensure the appropriate level of road safety. Furthermore, the comparison of the level of road safety in turbo roundabouts equipped in raised lane dividers with turbo roundabouts with lane separators in the form of continuous line revealed that turbo roundabouts with raised lane dividers are safer solutions than turbo roundabouts with traffic lane dividers in the form of continuous line.
Turbo roundabouts have been a popular choice of road intersections in the European countries in recent years, since they have better operational and safety performance than conventional roundabouts. ...To serve the heavy traffic demands, signal controls can be implemented on turbo roundabouts. The objective of this study is to clarify the specific traffic conditions, under which signalized turbo roundabouts are selected to install compared with signalized intersections. The twice-stop-right-turn control method is used for turbo roundabouts under the left-hand driving system. A signal control optimization model for turbo roundabouts is developed. Sensitivity analysis is made to capture the influence of entry volume and the right-turn movement ratio on capacity and average delay. Furthermore, the trend of the capacity of roundabouts with the radius of the central island is studied. It is found that under heavy balanced entry volumes, signalized turbo roundabouts have better operational performance than signalized intersections.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Replaces single-lane by turbo-roundabout and yield- and Stop-controlled RCUT.•Collects traffic, pedestrian, and cyclist data from two single-lane roundabouts.•Uses microscopic models to assess ...traffic performance, emissions and driving volatility.•Turbo-roundabout generally yields the lowest travel times and CO2 and NOx emissions.•Yield-RCUT is the best option concerning idling times, queues, and speed indicators.
This research explored the potential of replacing conventional single-lane roundabouts by turbo-roundabouts and yield- and stop-controlled restricted crossing U-Turn (RCUT) at intersections located in urban corridors. A simulation approach based on a well-integrated assessment of traffic performance, emissions and driving volatility indicators of alternative intersection designs (AIDs) is therefore a major contribution of the study. The paper also addressed the impacts that several locations of the U-Turn crossovers have on travel and idling times, as well as on carbon dioxide and nitrogen oxides emissions. Traffic, pedestrian, and cyclist flow data were collected from two urban three-leg single-lane roundabouts. A microscopic simulation platform of traffic and emissions (respectively, VISSIM and vehicle specific power) was used to evaluate intersection-specific design and operations. The results indicated that turbo-roundabout and yield-controlled RCUT outperformed the existing single-lane roundabout at the two sites. Turbo-roundabout generally yielded the lowest travel times and emissions compared to the other intersections. The Yield-RCUT also performed better than the single-lane roundabout for U-Turn crossover located 100–170 m from the main intersection. Our findings bring a solid basis for academic research and transportation planners to promptly consider the implementation of AIDs and contribute to sustainable mobility in cities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Objective: In this work, a roundabout and a turbo roundabout model are compared and previous modeling with continuous Petri nets and safety are analyzed through indicators of complexity. Petri nets ...are a graphic and mathematical representation that allow a faithful modeling of urban systems.
Method: The methodology has been designed for the transformation of a real system to small subgraphs that represent the maneuvers in roundabouts, approximated as roads and lanes of incorporation. Places within the roundabout have been located and defined as continuous places from their influence and visibility toward adjacent conditions. The transitions have been modeled by time and inhibitory arcs, which represent priorities and areas where drivers must pay attention. The created networks represent a faithful model of vehicle flow trajectories in the roundabouts.
Results: The methodology is applied to the same real road intersection. The case study is a recent transformation from roundabout to turbo roundabout. The roundabout network complexity is corroborated by a greater number of entries and exits that lead to each roundabout place (reflected in the maneuvers that can be performed) and a greater number of inhibiting arcs. In most of the turbo roundabout places, the driver's only option is reduced to occupying next place. The possibility of choosing between several places supposes a greater trajectory intersection and an increased time for decision making. The only situation where the complexity is the same between both systems is when a vehicle accesses the inner lane of the roundabout from the left lane on a single-lane road. The main maneuvers causing accidents have been modeled and their solution in a turbo roundabout is presented.
Conclusions: The reduced complexity of the turbo roundabout is due to the strict limitations in lane changes, turning turbo roundabouts into a safer model: A lower number of possible movements that can be performed by drivers and a smaller number of trajectories with collision risk. Petri nets have proven to be perfectly applicable to the representation of traffic circular systems (such as roundabouts and turbo roundabouts) and to measure the complexity and security of the system.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
In recent years, numerous turbo-roundabouts have been built in many European countries. To date, there are no turbo-roundabouts in Italy and even the regulations do not provide for their ...implementation. Turbo-roundabouts are considered the ideal alternative to multi-lane roundabouts as they have numerous advantages. However, they offer better operational performance only for specific traffic flow distributions. This research used the case study of an important and complex urban arterial road in eastern Sicily, Italy, to compare the operational and safety performance between multi-lane roundabouts and turbo-roundabouts. The evaluations were carried out with two simulation software: (1) AIMSUN Next 20.0.1 (operational performance); (2) SSAM 3.0 (safety performance). The results show that at medium/low traffic volumes, multi-lane roundabouts are significantly superior to turbo-roundabouts in terms of operational performance. At high traffic volumes, the operational performance of turbo-roundabouts improves significantly. As regards the safety parameters, for turbo-roundabouts there is always an increase in the TTC and PET, a reduction in maximum speeds and decelerations. There is also a significant decrease in conflict points. Ultimately, the safety and efficiency performance of turbo-roundabouts should: (1) Encourage administrations to replace the multi-lane roundabouts (illegal in Italy) with turbo-roundabouts; (2) encourage Italian legislators to revise intersection design legislation to include turbo-roundabouts among possible design solutions.
A microsimulation approach was carried out in this paper to evaluate the safety performance of turbo roundabouts in which the "CAVs" of connected autonomous vehicles are mixed with the "CVs" of ...conventional vehicles the research aims to evaluate the advantages in terms of safety and performance of turbo roundabouts. The paper shall also lead to describe the methodological path followed to build VISSIM models of turbo roundabout changing O-D matrix as real case applications, to calibrate the simulation models, and to estimate the potential conflicts when the percentages of CAVs are introduced into the traffic mix. The results, in accordance with the existing bibliography, have shown that the safety levels and the parameters that determine an improvement in the service level in a turbo roundabouts are significantly influenced not only by the geometric characteristics, but also by the distribution of vehicular flows. Therefore, it follows that in absence of crash data including CAVs, the surrogate measures of safety must be considered a strong approach to evaluate the safety performance of a roundabout so far, any road entity.
The paper presents a microsimulation approach for assessing the safety performance of turbo-roundabouts where Cooperative Autonomous Vehicles “CAVs” have been introduced into the traffic mix ...alongside conventional vehicles “CVs”. Based on the analysis of vehicle trajectories from VISSIM and subsequent analysis of traffic conflicts through the Surrogate Safety Assessment Model (SSAM), the research aims to evaluate the safety benefits of turbo-roundabouts where the lanes are physically separated by raised curbs, compared to roundabouts without such curbs. The paper will then describe the methodological path followed to build VISSIM models of turbo-roundabouts with and without raised curbs in order to calibrate the simulation models and estimate the potential conflicts when a higher percentage of CAVs are introduced into the traffic mix. A criterion has been also proposed for setting properly the principal SSAM filters. The results confirmed both higher safety levels for turbo-roundabouts equipped with raised lane dividers compared to turbo-roundabout solutions without curbs, and better safety conditions under the traffic mix of CVs and CAVs. Therefore, it follows that, in absence of crash data including CAVs, the surrogate measures of safety are the only approach in which the safety performance of any roundabout or road entity can be evaluated.
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