Turbo Roundabouts Research Articles

AN EVALUATION OF TURBO ROUNDABOUT PERFORMANCES: CASE STUDY OF THE CITY OF OHRID

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 and 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.

Assessment of Turbo and Multilane Roundabout Alternatives to Improve Capacity and Delay at a Single Lane Roundabout Using Microsimulation Model Vissim: A Case Study in Ghana

A single lane roundabout characterized by long queues during morning and evening peak periods was chosen as our study site. The objective of this study was to 1) Model and calibrate the vissim simulation model for the roundabout and 2) to model roundabout alternatives to improve capacity and assess the delay. A two hour video data collection was undertaken on a typical morning peak from which the traffic demand and turning movement data were extracted. The vissim micro simulation model was calibrated using the west approach as the target and the analysis was done for the existing single lane roundabout. A Turbo roundabout and a conventional double lane roundabout alternatives were also assessed. The capacity of the single lane roundabout was estimated as 2990 pcu/h and was performing at an ICU level of service H. Average Delay on the west approach was 232 seconds. The intersection capacity was 4392 pcu/h when the turbo roundabout alternative was assessed. Westbound vehicles experienced average delay of 87 seconds (inner lane) and 74 seconds (outer lane). The capacity of the conventional double lane roundabout was estimated to be 3690 pcu/h. The turbo roundabout concept will deliver a comparatively higher capacity and could be the most effective alternative to reduce congestion and delay.

MODERN TURBO-ROUNDABOUTS AND THEIR DESIGNING IN THE CZECH REPUBLIC

Even though the turbo roundabouts have been designed in the Czech Republic since the beginning of this century, until the middle of 2015, there was no national regulation which would describe the way of their construction. As a result of this, there are only 10 turbo-roundabouts with various widths of design elements and different traffic signs in the Czech Republic now. From this number there are some that even cannot be considered a turbo-roundabout. The aim of this paper is to present the results we gained within the research project and to present readers with the approach to the construction of geometry of turbo-roundabouts in the conditions of Czech road network and existing legislation and standards.

Design of Turbo Roundabouts Based on the Rules of Vehicle Movement Geometry

This paper describes a turbo roundabout design procedure based on the rules of design vehicle movement geometry. Previous studies carried out on various junction types have shown that this design approach ensures the usage of optimal roundabout element dimensions as well as safety and comfort during driving. A five-step design procedure is suggested, including a detailed description of relevant influential parameters. They are choosing a design vehicle, implementing the initial roundabout scheme on which the vehicle swept path is analyzed, choosing a method of assigning input parameters for swept path requirements testing procedure, choosing optimal design elements of a standard turbo roundabout, and fastest path vehicle speed analysis.

Operational Effects of Special Roundabouts at Large-Scale Rotaries

PURPOSES : The goal of this study is to analyze the operational effects of special roundabouts at large-scale rotaries in Korea. In pursuing the above, this study gives particular attention to comparing standard roundabouts with special roundabouts. METHODS : This study reviews the various types of roundabouts, creates 270 scenarios, builds networks, and comparatively analyzes the operational effects by using VISSIM simulation model and SSAM(Surrogate Safety Assessment Model). RESULTS : First, the operational effects of standard and signalized roundabouts were analyzed, and it was determined that standard roundabouts are the best in the case of under-saturated traffic volume, and signalized roundabouts are the best in the case of over-saturated traffic volume. Second, the operational benefits of a Turbo roundabout were evaluated to be generally lower than the benefits of a standard roundabout, and the benefits of a Turbo roundabout increase when right-turn traffic volume increases. Finally, the safety conflicts of a Turbo roundabout were determined to be the least and decrease when right-turn traffic volume increases. CONCLUSIONS : This study suggests that Turbo roundabouts rank highest for safety, and signalized roundabouts are best for over-saturated traffic volume. This study can be expected to provide some implications for policy decision-making.

Conversion of a Semi-two Lanes Roundabout into a Turbo-roundabout: A Performance Comparison

In the last years, as regards the functional design of at-grade intersections, near to classic layouts (signal-controlled junctions, roundabouts, etc.) a new solution has born: the “turbo-roundabout”. It is a canalized multilane oval intersection with a non-traversable or partially traversable center island and with a spiral circulatory carriageway. This kind of roundabout is also characterized by a predictable lane use: some direction flows are physically separated by curbs. Several roundabouts with spiraling circular carriageways were built in northern Europe (in particular in Netherlands) and they have further allowed to extend the notable advantages of this functional solution against multilane roundabouts, such as: 1) no lane changing on the circulatory carriageway; 2) no need to yield to traffic flow on more than two lanes; 3) low driving speed along the through movement because of raised lane dividers and, consequently, a high reduction of accident risk. In this paper a careful literature review on turbo-roundabouts is proposed. Furthermore, the Authors examine the potentialities offered by the transformation of an existing semi-two lanes roundabout into a “virtual” configuration of a turbo-roundabout. In particular, they also evaluate and compare the performance parameters in the two configurations by using a microsimulation software. The case study roundabout is placed in the city of Cosenza (Southern Italy) and it is characterized by great problems of congestion during peak hours. Experimental measures of traffic flows (O/D matrixes), critical gaps, queue lengths and approaching and circulating speeds represent input data for calibration procedures. Afterwards, derived calibration parameters are used as input variables for the new configuration of the intersection as a turbo roundabout. The Authors highlight that the conversion of the existing roundabout into a virtual turbo roundabout determine an increase of capacity together with a minimization of the queue lengths.

USING A MICROSIMULATION TRAFFIC MODEL TO COMPARE TWO-LANE AND TURBO-ROUNDABOUTS

Microsimulation traffic models are used to analyze and predict the functionality and safety of traffic networks, especially in critical areas such as intersections. These models have proven particularly useful in analyzing and comparing solutions in the early stages of design. In this paper, we compare the functional characteristics of an existing two-lane roundabout and a proposed replacement turbo roundabout. Our microsimulation modeling used the VISSIM traffic model, and we designed the conceptual turbo roundabout with AutoCAD and TORUS5 Roundabouts software.

Gap-accepteance parameters for roundabouts: a systematic review

The critical and follow-up headways are the two gap-acceptance parameters which explain the traffic interaction of a minor street vehicle when enters the roundabout, merging into or crossing one or more circulating (major) streams. Several studies and researches provide measurements of critical and follow-up headways from real data at roundabouts. The objective of our research is to synthesize the data from the series of selected studies to interpret variation across the studies. In order to match the research goal, a systematic literature review on estimations of critical and follow-up headways at roundabouts was undertaken. Since several studies and researches developed worldwide were examined, we were able to note that the effect size varied from study to study. Thus the meta-analysis of effect sizes was performed as part of the literature review through the random-effects model. After discussing the assumptions of this model, the dispersion in effects across studies was assessed and the summary effect for each of the parameters under examination was computed. Calculations were made both for single-lane roundabouts and double-lane roundabouts, as well as for turbo roundabouts. Compared to the results of individual studies, the single (quantitative) meta-analytic estimate provides an accurate and reliable synthesis on the specific issue here addressed, and gives, with greater power of the individual reviewed studies, a comprehensive measure for the parameters of interest.

An Operation and Safety Assessment Study of Roundabout Types

PURPOSES: The aim of this study is to analyze and compare the operational effectiveness and safety of three different types of roundabout found in the literatures using a VISSIM and SSAM program. METHODS : The three types roundabout tested are the 2-lane roundabout (2R), the Turbo roundabout (TR), and the Flower roundabout (FR). For each scenario, three roundabout types and traffic conditions such as traffic volume and movement ratio were applied to VISSIM in order to compute the average delays. In addition the total conflict was calculated through SSAM by using trajectory data from VISSIM. RESULTS: From the analysis results, the average delay in TR and FR type was higher than the 2R. Regardless of the roundabout types, the average delay was reduced as the right-turn vehicles increased. The total conflict in TR was fewer than 2R for all traffic conditions. CONCLUSIONS : The results of this study can be used in the planning and design process of roundabout deployment. The data also provides some numerical justifications in transition from at-grade intersection to roundabout.

THE ROAD SAFETY AT TURBO ROUNDABOUTS IN POLAND

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.

Evaluation of the safety performance of turbo roundabouts by means of a potential accident rate model

Turbo roundabouts are a particular road intersection layout, designed to increase the safety of double-lane roundabouts, while maintaining their excellent capacity. The main feature of this new concept of roundabout is the impossibility to move from one lane to another, provided by physical barriers marking the lanes. The paper shows an application to turbo roundabouts of a potential accident rate model, aiming to evaluate their safety improvement. Themodel is based on the concept of potential conflict: each vehicle involved in a general intersection performs a series of maneuvers which potentially imply a crash, according to the actual traffic. The number of accidents related to each critical maneuver is proportional to the number of times this maneuver occurs at the intersection. In order to define the critical maneuvers, and hence the relevant potential conflicts, specific crash typologies for roundabouts are adopted. Traffic volumes are required, to evaluate the expected number of accidents, and also probabilities of accident for every critical maneuver. These ratios were obtained by a model calibration, based on actual accident and traffic data recorded on conventional single and double-lane roundabouts. The model was then used to compare four-leg turbo roundabouts to conventional roundabouts. The comparisons have taken into account only basic differences in layout, such as geometric elements, that also play a role in determining safety performances of a roundabout. The results obtained show that turbo roundabouts significantly decrease the accident rate with respect to conventional roundabouts, by eliminating conflicts between circulating and exiting vehicles.

Calculation of Turbo-Roundabouts with Slip Lanes

A turbo roundabout is a particular type of roundabout where all lanes are bounded by traffic signs and by non-mountable curbs installed at entering and circulating lanes. Turbo roundabouts also have a very particular shape to accomplish the splitting of traffic streams and to prevent cars weaving through. These aspects make turbo-roundabouts more appropriate than roundabouts when a higher level of safety has to be guaranteed, particularly in presence of relevant pedestrian and two-wheels traffic volumes. Only in some traffic conditions, turbo roundabouts can offer higher capacities than conventional double-lanes roundabouts, so if more capacity must be guarantee a bypass lane can be added to the turbo roundabouts layout. This paper presents a closed-form model for the estimation of capacity, delays and level of service of turbo-roundabout equipped with Right-turn bypass lanes, considering the effect of geometric slip lane schemes, control type, vehicular and pedestrian flow.

Reducing Air Pollutants through Road Innovative Intersections

Road pollutant emissions are correlated mainly to infrastructural capacity and to traffic intensity and typology. With the aim to improve road intersections performances in the last years was designed many new geometric layouts, like turbo roundabouts and flower roundabouts. The main objective of this paper is carried out a comparative analysis between conventional and innovative roundabouts in terms of CO, CO2, NO and PM2,5 vehicular emissions, evaluated by means of COPERT Software which is developed as a European tool for the calculation of emissions from the road transport sector.

Estimation of Air Pollutant Emissions in “Turbo” and in Conventional Roundabouts

The road pollutant emissions, above all in urban context, are correlated to many infrastructural parameters and to traffic intensity and typology. The research work on road junction geometry, carried out in European research centres, has recently allowed to design new road intersection types which are of undoubted interest, especially in terms of traffic functionality and safety, like the turbo roundabouts (in which right-turn manoeuvres do not conflict with the circulating flow). The main objective of this paper is to propose a model for the estimation the performances and the pollutant emissions into turbo roundabouts. A comparative analysis between conventional roundabout and turbo roundabout has been carried out in terms of CO, CO2, CH4, NO, PM2,5 and PM10 vehicular emissions, evaluated by mean of COPERT Software which is developed as a European tool for the calculation of emissions from the road transport sector.

Performance Analysis of Basic Turbo-Roundabouts in Urban Context

A turbo roundabout is a new type of canalized multilane intersection in which the physical separation between lanes helps to prevent side collisions when crossing the roundabout. This paper presents an estimation of capacity, delays and level of service of basic turbo roundabouts in undersaturation conditions, considering both vehicle flow and pedestrian traffic. The traffic performance model was developed by evaluating the capacity for each entry lane. Owing to the geometric features of the intersection, the total entry capacity is obtained by considering different values of the pedestrian impedance factor and degree of saturation at both the right-turn and left-turn lanes.

Conversion of Existing Roundabouts into Turbo-Roundabouts: Case Studies from Real World

Compared with roundabouts the main advantages of turbo-roundabouts are the reduction in the number of potential conflicting points and the lower speed of vehicles passing through the intersection, they both can improve safety conditions at the junction. Moreover, the physical delimitation among lanes limits the side-by-side accident risk. These aspects make turbo-roundabouts more appropriate than roundabouts when a higher level of safety has to be guaranteed, particularly in presence of relevant pedestrian and two-wheels traffic volumes. The present paper has three main objectives: (1) to discuss general design criteria and functional principles of turbo roundabouts, (2) to give the geometric design principles of the central island and circulating lanes and (3) to present three case studies from real world concerning the conversion of existing roundabouts into turbo roundabouts.

New Type of Roundabout: Roundabout with “Depressed” Lanes for Right Turning – “Flower Roundabout”

Recently, many of the foreign traffic-safety analyses point out the low level of traffic safety in multi-lane roundabouts. This problem is resolved in several ways in different countries; however, the solution, whereby the number of conflict points is diminished (e.g. turbo roundabout) has proven to be the most successful. However, the turbo roundabout also has its deficiencies: it has conflict crossing points and larger reconstruction of the existing two-lane roundabout is needed when the turbo roundabout is to be implemented instead of the existing one. In the paper a new type of roundabout has been introduced; the roundabout with “depressed” lanes for right turning (“the flower-roundabout”). Financially speaking, the main advantage of the new type of roundabout is that it can be implemented within the dimensions of the already existing “normal” two-lane roundabout. From the traffic-safety point of view, the main advantage of the new type of roundabout is that it has no crossing conflict points. KEYWORDS: traffic safety, roundabout, turbo roundabout, roundabout with “depressed” lanes for right turn

Turbo Roundabouts

While concentric two-lane roundabouts have a higher capacity than single-lane roundabouts, they have the disadvantage of a higher driving speed through the roundabout. They also reintroduce the possibility of lane changing on the roundabout and hence raise the risk of accidents. The author developed the turbo roundabout in 1996 in an attempt to deal with these drawbacks. This type of roundabout has the following features: no lane changing on the roundabout, no need to yield to traffic on more than two lanes, and low driving speed through the roundabout because of raised lane dividers. This paper discusses the concept of the turbo roundabout and the details determining success. Studies have shown that the risk of accidents associated with injury is greatly reduced on turbo roundabouts: an 80% reduction has been measured. In view of the known safety trends on single-lane roundabouts, it is recommended that a slightly lower reduction in the accident rate (70%) should be assumed in the long term. Another great advantage of the turbo roundabout is the fact that the traffic flow can be divided over the lanes of the roundabout in a much more balanced way. Since 2000, 70 turbo roundabouts have been built in the Netherlands. The Dutch Information and Technology Platform (CROW) published its guidelines on turbo roundabouts in April 2008.

Turbo Roundabouts

The Dutch turbo roundabout is characterized by predictable lane use and radial connecting entries. To calculate the capacity, in 1997 the multilane roundabout explorer was developed by modification of the capacity model of Bovy, which considered both separated lanes and pseudoconflict. Because of its linear structure, this model did not take into account multilane roundabout properties in a good way. Therefore a new model was developed by modification of the model of Hagring. Using only the gap acceptance approach to calibrate the parameters is not sufficient because the pseudoconflict is not taken into account. A combination with a stream approach is necessary. For validation of an analytic model, it is important to realize that the distribution of gaps offered in two flows simultaneously is determined primarily by a stochastic process. Thus, it is possible to test the effect of the distribution of the flows over two circulatory lanes by using a microsimulation model. The parameters needed to tailor VISSIM microsimulation software for this purpose were estimated. It is concluded that a VISSIM model may be suitable for the analysis of both single-lane and two-lane roundabouts. This paper deals with this combined approach. The findings are that ( a) the pseudoconflict should be taken into account and ( b) the turbo roundabout will have a larger capacity than the Dutch standard concentric double-lane roundabout because of the better circulatory lane-split.