Lane Roundabouts Research Articles

Turbo roundabout - An alternative to classic two lane roundabout

Traffic congestion and the questionable safety of two-lane roundabouts are two justified criteria for the introduction of turbo roundabouts. The increase in capacity, which also results in an increase in the level of service, is a positive aspect of this alternative type of roundabout. Also, reduced number of conflict and collision points at the exits and intersections at the turbo roundabout as well as lower vehicle speed, increase safety, compared to classic two-lane intersection. The mentioned advantages justify the need for improving existing overloaded roundabouts.Therefore, the subject of this article is the reconstruction of the existing two–lane roundabout with two entrances and exits, in Podgorica, at the intersection of “Josipa Broza Tita Street” and “V Proleterske brigade Street”, into a turbo roundabout.

Improving cycling safety through infrastructure design: A bicycle simulator study

This study investigated the impact of two road treatments on cyclist behaviour using an bicycle simulator. The treatments were sharrows (presence or absence) at a roundabout and widening an on-road bike lane (width 1.2 m or 1.8 m) on a curved mid-block section of the road. Outcomes collected included count (e.g. number of lane excursions) and continuous responses (lane position upon entry into the roundabout, in metres from the curb). A convenience sample of 21 Perth-based participants was recruited between 1 July and 30 September 2021. The results found that the presence of sharrows was not significantly associated with the distance from the left curb when entering a single lane roundabout. However, females rode 0.44 m further from the left curb when entering the roundabout than males, which was significant (95 % CI = 0.02–0.85; p = 0.04). Riders, aged 26–40 years, also rode 0.61 m further from the left curb when entering the roundabout than riders aged 18–25 years, which was also significant (95 % CI = 0.18–1.05; p = 0.01). The rate of bike lane excursions significantly decreased by 68 % for the wide bike lane on the curved mid-block section of the road compared to the standard width bike lane (IRR = 0.32; 95 % CI = 0.11–0.88; p = 0.03). Riders, aged 26–40 years, had a significant increased rate of 8.72 excursions than riders aged 18–25 years (IRR = 8.72; 95 % CI = 3.32–22.89; p < 0.001). This study highlights that increasing the bike lane width on curved sections of mid-block roads may benefit cyclists. However, the value of sharrows in a single lane roundabout is less clear.

Connected vehicles at single lane roundabouts and its performance evaluation

Connected vehicles (CVs) have led to innovative changes in the transportation field. In this wise, an extended CA model was established incorporating the CVs and regular vehicles to investigate a roundabout traffic flow under the open boundary condition. The throughput and the phase diagrams of the system in the ([Formula: see text]) area is constructed in both cases: with and without CVs. The density profile and the capacity are also calculated. The simulation findings show that CVs presentation changes the traffic dynamics, enhancing roundabout capacity in accordance with the CVs penetration rate. Furthermore, it is found that roundabout size plays a dominant role in its performance where it suggests that the midsized roundabouts operate more optimally. Another relevant aspect is the short sized of Splitter Island shows a better performance. Moreover, the traffic dynamics is negatively (resp. positively) correlated to the probability of displaying indicator [Formula: see text] as well as the probability of aggressive driving behavior of regular vehicles (resp. the cooperation probability [Formula: see text]).

Relationship between Critical Gap and Certain Geometrical Parameters in Roundabouts

Gap-acceptance method is one of the classical methods used to analyze capacity of roundabouts. Critical gap has a privileged role in this approach. Different driver behavior and local rules of traffic has a key role in implementing it in the local standard for capacity calculation in each country. Therefore, a reliable method for estimation of critical gap at a certain location can be of great importance. This paper presents the first steps of an experimental investigation and analysis on whether it is possible to find correlation between video-based gap acceptance data and certain design parameters of roundabouts in Hungary. Ten single lane roundabouts of different size were recorded for hours in different locations in and around Budapest to assess gap acceptance data and relate it to certain design parameters like diameter, distance of neighboring entries, entry width, width of splitter island, number of entries over time, and entry angle – or any combination of those. Using only a linear approach, strong positive correlation was found between measured critical gap and distance between legs. There is correlation (not so strong however) between critical gap and (approach) entry width as well as splitter island width, and enough data were examined to say that there is no correlation between central island diameter and critical gap.

Critical Gap in Roundabouts – A Short Comparison of Estimation Methods

Gap-acceptance method is one of the classical methods used to analyze the capacity of roundabouts. Critical gap has a privileged role in this approach. Different driver behavior and local rules of traffic have key role in implementing gap-acceptance method into the local standard for capacity calculation in each country. Therefore, a reliable method for estimation of critical gap at a certain location can be of great importance. This paper presents an experimental investigation and analysis on whether it is possible to find differences between estimating critical gap using video-based gap acceptance data of roundabouts in Hungary. Three single lane roundabouts of different size were recorded for hours in different locations in Budapest and Érd to assess gap acceptance data. Three different methods or models were used to estimate critical gap and no significant differences were found between their results.

Connected automated vehicle control in single lane roundabouts

This paper introduces a methodology to optimize the trajectory of connected automated vehicles (CAVs) in roundabouts using a two-dimensional point-mass model. We formulate an optimization problem that includes vehicle dynamics and collision-avoidance constraints with explicit representation of vehicle paths. The objective function of the problem minimizes the distance of CAVs to their destinations and their acceleration magnitudes. The methodology also involves a customized solution technique that convexifies the collision-avoidance constraints and employs the alternating direction method of multipliers to decompose the convexified problem into two sub-problems. The first sub-problem only includes vehicle dynamics constraints while the second sub-problem projects the solutions of the first sub-problem onto a collision-free region. The first sub-problem is then transformed into a quadratic problem by redefining its decision variables along vehicle paths. The transformation allows solving this sub-problem with several vehicle-level problems in a distributed architecture. Moreover, we show that iterating between the two sub-problems leads to convergence to the optimal solutions of the convexified problem. The methodology is applied to a case study roundabout with different demand levels. The results show that the trajectory optimization reduced the total travel times and average delays respectively by 9.1% to 36.8% and 95.8% to 98.5% compared to a scenario with human-driven vehicles.

Analysis of gap parameters for the estimation of single lane roundabouts’ capacity in the State of Qatar

Abstract Entry capacity is an important parameter for evaluating the roundabout performance. In general, entry capacity is influenced by three gap parameters: critical gap, follow-up time and minimum headway of circulating vehicles. These gap parameters certainly are correlated with the driving behavior as well as the roundabout characteristics. In this paper, video records of two single roundabouts in the state of Qatar were used to estimate the gap parameters. In addition, the entry capacity of both roundabouts was estimated and compared through different methodologies. Results showed that the entry capacity is directly related with the inscribed circle diameter (ICD) until 400 vph of circulating flow. However, it is inversely related with ICD if the circulating flow exceeds 400 vph. Moreover, we found that the entry capacity has a negative relation with the gap parameters. Estimated entry capacities with the calibrated Highway Capacity Manual 6th Edition model (HCM, 2016) were significantly higher than estimated ones through the proposed approach by Qatar Highway Design Manual (QHDM, 2015). Interestingly, the entry capacity was underestimated in both approaches if default gap parameter values are used compared to the calibrated models using the observed gap parameters (36.7% less for HCM, and 19.4% less for QHDM). Thus, the utilization of realistic gap parameter values representing local traffic condition is essential for traffic planners to accurately estimate the entry capacity and accordingly ensure feasible design of different types of roundabouts.

Imitating a Safe Human Driver Behaviour in Roundabouts Through Deep Learning

Roundabouts provide safe and fast circulation as well as many environmental advantages, but drivers adopting unsafe behaviours while circulating through them may cause safety issues, provoking accidents. In this paper we propose a way of training an autonomous vehicle in order to behave in a human and safe way when entering a roundabout. By placing a number of cameras in our vehicle and processing their video feeds through a series of algorithms, including Machine Learning, we can build a representation of the state of the surrounding environment. Then, we use another set of Deep Learning algorithms to analyze the data and determine the safest way of circulating through a roundabout given the current state of the environment, including nearby vehicles with their estimated positions, speeds and accelerations. By watching multiple attempts of a human entering a roundabout with both safe and unsafe behaviours, our second set of algorithms can learn to mimic the human’s good attempts and act in the same way as him, which is key to a safe implementation of autonomous vehicles. This work details the series of steps that we took, from building the representation of our environment to acting according to it in order to attain safe entry into single lane roundabouts.

CAVs and roundabouts: research on traffic impacts and design elements

Roundabouts’ design combined with gradual changes in vehicle characteristics entails that the existing layouts need to be examined to a wider range of scenarios. Nowadays, the modern automotive industry is facing a revolution that is possible to lead the introduction of automated vehicles for use in everyday traffic. This paper investigates the traffic impacts, as well as the possible changes in the design elements needed by the introduction of automated and connected vehicles on double lane roundabouts. Two case study roundabouts were examined. Different CAV penetration rates were established regarding assertive and defensive driving behavior of CAVs. The assumptions and the parameters for modeling the driving behavior of CAVs were selected according to recent studies and experiments. Results indicate several benefits in terms of operational performance regarding the introduction of CAVs on traffic flow and possible needs for changes in the design elements.

Analysis of the functional efficiency of small town arterial thoroughfare (Case Study of Našice Town)

The main factors that affect the choice of the intersection type when constructing a new or reconstructing an existing intersection are desired traffic flow rate and achievable traffic safety. At the same time, a significant challenge is to find optimal solutions for (re)construction and traffic organization at intersections in settlements, especially in agglomeration centers, due to their specific and, in most cases substantial, spatial and traffic constraints. This paper presents the examination of the functional efficiency of the introduction of roundabouts in the road network of Našice Town. As the location for the analysis, a section of county road 4168 is selected, which includes two consecutive 4-legged signalized intersections. For the purpose of the investigation presented in this paper, these signalized intersections are to be substituted with two single lane roundabouts. Conceptual design of these roundabouts includes prescribed performance checks: swept path analysis, speed and visibility checks. Finally, the rating of the analyzed road corridor functional efficiency and dynamics of intersections reconstruction is given based on the defined levels of service for the current state and the intersection reconstruction proposals.

Influence on the Type of Intersection on Road Traffic Safety in Poland

Analysing accidents in Polish towns it can be seen that a great majority of them occur at intersections. Moreover, it can be observed that some types of intersections are particularly dangerous. Hence, a question arises: which types of intersection can be considered to be more dangerous and which ones less dangerous? It needs to be emphasized that engineering projects do not include guidelines of this type. For designers of road infrastructure this kind of knowledge is very important. Therefore, the article aims at determining the degree of risk to a road traffic user, depending on the intersection type. The risk degree was defined as an average number of accidents falling on 1 vehicle and one traffic lane at the intersection inlet. Data on accidents which occurred in selected Polish towns during 3 years was used. In order to provide diversification of the intersections, each group included intersections with lower and higher significance for the city transport network so the traffic intensity was different for different intersections. The mean risk index as well as the dependence between the number of accidents and a variable characterizing the likelihood of collision were determined for each intersection type by means of regression analysis. Multi-lane roundabouts and intersections with a central island and extended inlets without traffic light signalling (both with right of way for one direction and the necessity of yielding way at each inlet) were found to be the most dangerous types of intersections. Intersections with priority to the right were found to be relatively dangerous, particularly those with traffic canalizing islands. Not channelized intersections with multi-phase traffic signalling were found to be potentially the safest ones. The research shows that single traffic lane roundabouts are potentially safe intersections, for which the risk degree is 2.5 times smaller than at multi-lane roundabouts.

ACFR Five Roundabouts Dataset: Naturalistic Driving at Unsignalized Intersections

This paper presents the ACFR five roundabouts dataset, a collection of over 23,000 vehicle trajectories of real world naturalistic driving at unsignalized intersections. This data was taken using a lidar based perception and tracking system onboard a stationary vehicle near the intersections. The focus of this dataset is single lane roundabouts, as these unstructured intersections have no signals dictating which vehicle has right-of-way, meaning that there is considerable negotiation between vehicles. The method for data capture is presented, as well as a study of the collected data including data preprocessing techniques and data analytics. The data preprocessing techniques are focused around preparing the data for machine learning training. The extensiveness of this dataset makes it essential to validate algorithms for state of the art ADAS and autonomous vehicles. The paper concludes with a focus study of some of the outliers in the data.

Factors with the greatest influence on drivers' judgment of roundabouts safety. An analysis based on web survey in Italy

The aim of this paper is to identify the roundabout geometric characteristics affecting the safety perception while the typical maneuvers (entry, circulation, exit) are being carried out. The tool used was an on-line questionnaire, filled out by about 1.650 respondents. Four different dimensionality reduction methods (Cluster Analysis, Correspondence Analysis, Exploratory Factor Analysis and Confirmatory Factor Analysis) were used to analyze the data collected from the survey, in order to examine the key factors affecting the safety perception during the typical roundabout maneuvers. The considerations arising from the final model are the following: 1) the respondents' opinions regarding the safety perception of maneuvers are not preconceived ideas, but they originate from specific safety perceptions due to roundabout geometric configurations; 2) the users prefer definitely single lane roundabouts; this is an important confirmation of most results in the literature; 3) it was quantified the extent of the relationship between the safety perception of the typical roundabout maneuvers and the following aspects: a) maneuver type, b) geometric characteristics of the roundabouts design elements. This is the innovative aspect of the present research whose results have implications regarding theory, infrastructure and the application of new safety technologies.

Simulating transit priority: Continuous median lane roundabouts

This paper describes and analyses a layout and regulation, which provides 100 % bus priority and no delays for buses at small and medium sized roundabouts. The Continuous Median Lane Roundabout (CMLR) is designed specifically for bus rapid transit (BRT) or buses with high level of service (BHLS), where buses run in median exclusive lanes. In previous solutions, access to the roundabout circulating lanes from the general purpose approach lanes has been controlled by traffic signals. In the CMLR, give way signs within the roundabout control the two conflict points between buses in the median lanes and other vehicles in the circulating lanes. Microsimulations show that there is a large and unused potential for transit priority at roundabouts. Significant reductions in delays and emissions may be achieved.

Case Study: Capacity Characteristics Comparison of Single-lane Roundabout and Turbo-roundabouts

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.

Simulation study of interference of crossings pedestrian and vehicle traffic at a single lane roundabout

Abstract This paper proposes a vehicle–pedestrian cellular automata model to investigate the characteristics of the mixed traffic at a single lane roundabout. The roundabout boundary is controlled by the injecting rates α 1 , α 2 and the extracting rate β whereas pedestrians are generated with arrival probability P cr . The pedestrian and vehicle flux are calculated in terms of rates. Also, the phase diagrams of the system in the ( α 1 , P cr ) and ( α 1 , β ) spaces are constructed. The results show that, the gridlock state is reached only when the pedestrians have the right of way over vehicles, while the maximum current state is reached when including a pedestrians’ crossing decision rule. Likewise, we have found that the crosswalk location play a chief role in improving the dynamic characteristics of pedestrian and vehicle flux. Furthermore, it has turned out that the traffic is sensitive to the driver behavior.

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.

A case study on multi-lane roundabouts under congestion: Comparing software capacity and delay estimates with field data

Existing studies on modern roundabouts performance are mostly based on data from singe lane roundabouts that are not heavily congested. For planners and designers interested in building multilane roundabouts for intersections with potential growth in future traffic, there has been a lack of existing studies with field data that provide reference values in terms of capacity and delay measurements. With the intent of providing such reference values, a case study was conducted by using the East Dowling Road Roundabouts in Anchorage, Alaska, which are currently operating with extensive queues during the evening peak hours. This research used multiple video camcorders to capture vehicle turning movements at the roundabouts as well as the progression of vehicle queues at the roundabout entrance approaches. With these video records, the number of vehicles in the queues can be accurately counted in any single minute during the peak hours. This study shows that unbalanced entrance flow patterns (i.e., one entrance has significant higher flow than others) can intensify the queue and delay for the overall roundabouts. Then various software packages including RODEL, SIDRA and VISSIM were used to estimate several performance measurements, such as capacity, queue length, and delay, compared with the collected field data. With the comparison, it is found that all the three software packages overestimate multi-lane roundabout capacity before calibration. With default parameters, SIDRA and VISSIM tend to underestimate delays and queue lengths for the multi-lane roundabouts under congestion, while RODEL results in higher delay and queue length estimations at most of the entrance approaches.

Phase diagram of a single lane roundabout

Using the cellular automata model, we numerically study the traffic dynamic in a single lane roundabout system of four entry/exit points. The boundaries are controlled by the injecting rates α1, α2 and the extracting rate β. Both the system with and without Splitter Islands of width Lsp are considered. The phase diagram in the (α1,β) space and its variation with the roundabout size, Pagg (i.e. the probability of aggressive entry), and Pexit (i.e. the probability of preferential exit) are constructed. The results show that the phase diagram in both cases consists of three phases: free flow, congested and jammed. However, as Lsp increases the free flow phase enlarges while the congested and jammed ones shrink. On the other hand, the short sized roundabout shows better performance in the free flow phase while the large one is more optimal in the congested phase. The density profiles are also investigated.