Urban Roundabouts Research Articles

Safety of bicyclists in roundabouts with mixed traffic: Video analyses of behavioural and surrogate safety indicators

Although converting an intersection into a roundabout has been shown to result in fewer injury accidents for both motor vehicle drivers and pedestrians, the effect on bicyclists’ safety is unclear or even negative. This study focuses on roundabouts without bicycle facilities (i.e., mixed traffic conditions) and makes use of semi-automated video observation software with the aim of analysing bicyclists’ behaviour and safety on roundabouts with different diameter. Four urban roundabouts in Belgium are observed. Interactions between bicyclists and other vehicles are analysed using speed, lateral position and five indicators to describe the closeness of interactions (TTCmin, PET, T2 min, lateral overtaking proximity and minimum distance headway). Additionally, the lateral position and riding speed of bicyclists that are in interaction with other vehicles is compared with the behaviour of bicyclists that are not in interaction with other vehicles.The behavioural analysis revealed that regardless of the type of condition (free-flow bicyclists or different interactions bicyclist-car), bicyclists always ride faster on roundabouts with big diameter and slower on roundabouts with small diameter. Moreover, bicyclists ride closer to the central island on roundabouts with big diameter compared to roundabouts with small diameter for all the conditions analysed.The analysis of surrogate safety indicators (TTCmin, PET, T2 min) revealed that close interactions between bicyclists and cars are relatively frequent at both small and big roundabouts. The percentages of close interactions are more or less equal for roundabouts with big diameter (7.86% of observed interactions) and roundabouts with small diameter (8.24%). The analysis of the indicators to describe the closeness of interactions also showed that the closest interactions at roundabouts are all situations where the bicyclist has a leading role. The analysis of the most common types of close interactions revealed indeed that the most common close interactions are interactions where the bicyclist is entering the roundabout. The analysis of lateral overtaking proximity showed that bicyclists who overtake a car take smaller lateral overtaking proximities compared to cars overtaking a bicyclist. The analysis of minimum distance headway finally revealed that bicyclists who ride behind a car take smaller distance headways compared to cars driving behind a bicyclist.

New Extensions and Applications of the Modified Chumanov Model for Calculating Entry Capacity of Single-Lane Roundabouts

Over the past decades many models for roundabout capacity have been proposed. Attention to this research sector has never stopped and still today new formulations are always being studied, especially in view of their direct application in design practice. This paper reports the first noteworthy results of a research concerning the Modified Chumanov (MC) model, which can be used to estimate the capacity of single-lane roundabout entrances. After a detailed examination of the original model recommended by the Russian guidelines for small urban roundabouts, the paper proposes some extensions which allow using the revised model even for larger intersections. The MC model also includes some parameterizations that allow its application with different road pavement surface conditions (i.e., dry and wet conditions). The MC entry capacity model, as function of circulating flow and other parameters dependent on geometry and environmental conditions, was compared with 15 widespread models considering a typical medium-sized single-lane roundabout. A validation test was carried out considering four capacity–circulating flow datasets from the literature. The proposed MC model showed good flexibility in adapting to data. This flexibility appears better than the most recent models by Highway Capacity Manual, in the absence of local calibration of the psychotechnical parameters.

Estimation of Critical Headway at Small Urban Roundabout

Before choosing an intersection project design, an important step is to examine the justification of the construction on the basis of defined criteria. One of the key criteria is the analysis of capacity. Large numbers of roundabout capacity models are present in the world, most of them adapted to the conditions of the country they originate from and they need to be calibrated for local conditions. Key parameters for calibration are critical headway and follow-up headway. Follow-up headway can be measured directly in the field, while critical headway cannot be measured, but is estimated. Many critical headway estimation methods exist (over 30) and each of them provides different values. Different values of critical headway result in different capacity estimation values. This raises the question which method provides more realistic estimations under certain conditions. In this paper, four most frequently used critical headway estimation methods (Raff, Maximum likelihood method, Wu, Logit) were selected to be tested by comparison of theoretical capacity models and actual measured capacity at a small urban roundabout.

Modification of SIDRA Model for Capacity Estimation of Urban Roundabouts under Mixed Traffic Condition in Sri Lanka

Modification of SIDRA Model for Capacity Estimation of Urban Roundabouts under Mixed Traffic Condition in Sri Lanka

Approach Alignment Impact on the Geometric Design of Urban Roundabouts

Nowadays existing three and four-leg intersections are frequently replaced by roundabouts. Compared to conventional intersections, the implementation of roundabouts on a road network offers several advantages, such as increased safety and intersection capacity, reduced maintenance costs and air pollution. However, in some cases, these are not realized because of the poor geometric design. One of the main prerequisites for the optimal roundabout design is that all the approach axes must intersect at the centre of a roundabout. The alignment of the approach axis relative to the centre of a roundabout plays an important role in the roundabout design. It affects the amount of deflection (the ability to control driving speed through roundabout), the swept path of a design vehicle and the sight distance. In practice, due to spatial constraints and increasing property development along the road, this precondition cannot always be satisfied. This comes to the fore particularly in urban environments, where the reconstruction of the approach axis is usually not possible. Considering the above, this paper will investigate the impact of the radial offset of approach axis (the axis does not pass through the roundabout centre) on the geometric design of urban roundabouts. The research is carried out through several theoretical examples of the small and medium-sized urban roundabouts with various external radii and for the design vehicle 12.0 m long bus.

Analysis of sight distances at urban intersections from a vulnerable users’ approach: A case study

Road elements are predominantly designed to safely accommodate motorized users. Urban roads and streets, unlike highways, contain very dissimilar users and might have higher points of conflict. Nowadays, due to the increasing use of vehicle sharing systems, personal transportation devices and bicycle-friendly policies, some urban streets have had to adapt to distinct users with different levels of vulnerability. Given the interest in increasing the use of alternative transportation methods, it is of great importance to make sure these car-centered designed roads provide securely for all users. In order to create a safe environment for these unalike users, common measures such as reducing speed limits, traffic calming interventions and modifications to the road geometry have been taken in several urban areas. In this regard, taking into account the key role that proper available sight distance plays in road safety, the visibility of an urban roundabout located in Madrid, Spain was evaluated. This analysis was performed considering the observers to be pedestrians, cyclists and electric scooter riders. In addition to the estimation of their crossing and stopping sight distances, their reciprocal visibility with drivers was assessed. Nowadays there are different ways of obtaining up-to-date information of the road scene and cycle lanes with sufficient accuracy and detail, hence it is possible to easily perform offsite analyses of distinct road parameters. Here, the virtual verification of sufficient stopping and intersection sight distances was performed utilizing a LiDAR derived digital terrain model and 3-D geometries. These evaluations were performed with the objective of identifying potential risk locations for these vulnerable users and the proposal of measures that could improve their safety.

Enriching complex road intersections from OSM with traffic-related behavioral information

Abstract. Bicycle traffic in urban environments has various complex aspects in relation to the used space and the assigned transport infrastructures, especially in urban environments. Depending on the traffic situations, the built static urban infrastructure design, and, the other traffic participants involved, there are more or less challenging possibilities of its representation. Modelling and simulating urban bicycle traffic should include the interactions to other traffic participants, and, of course, behavioral aspects within each ride. Therefore, we introduce a method for enriching road features from OSM with traffic-related behavioural information. We focus on road intersections, since those are the locations with the highest number of interactions, communications, and, accidents. Our aim is to extend microscopic traffic flow simulations for achieving higher accuracies in simulation results and for applying bicycle movement models that are more adapted to reality. As an example we present a behavioral catalogue for cyclists, focussing on urban roundabouts, which results from real video observations and subsequent classifications.We classify into typical, frequently occurring and unusual bicycle maneuvers, and, include those into a specification procedure when enriching various OSM features.

Implementation of Shallow Underpasses at an Urban Roundabout

Implementation of Shallow Underpasses at an Urban Roundabout

Green Mobility Infrastructures. A landscape approach for roundabouts’ gardens applied to an Italian case study

The paper presents a multi-criteria method for unitary projects related to open spaces along urban road networks, with a focus on green spaces at roundabout intersections, considering them as integral part of broader landscape systems, and therefore as an opportunity for the construction of green infrastructures. The sprawl of road networks and the evolution of their types have gradually created a remarkable repertoire of new categories of open spaces, which, despite their often small size and residual nature, collectively can no longer be neglected. Innovative urban planning can transform these residual spaces into a distinctive feature of the city. Within this framework, we present a case-study on green spaces inside and adjacent to urban roundabouts in the City of Imola (Bologna), in the Emilia Romagna Region (Italy). They have been conceived as gardens, in order to enhance cultural values and foster a responsible use of environmental resources. The novelty of work lies in the holistic and cross-scale approach. Our proposal is based on a combination of multiple design issues (scenic values, landscape ecology, socio-economic sustainability) and specific characters of the context, with the aim of fulfilling aesthetic and functional requirements at the landscape level. The study defines spatial composition criteria, vegetation abacus and maintenance plans, articulated according to the various systems we identified and the following greening categories: Wild Flowers areas, Urban Groves, Rain Gardens, and Dry Gardens. We provide planning and design tools as guidance for further exploration. Concepts and guidelines we define enrich the discussion on mobility-related green spaces and integrate the few indications and instances on landscaping at roundabouts reported in the literature.

Traffic flow behavior at a single-lane urban roundabout

In this paper, we propose a stochastic cellular automata model to study the traffic behavior at a single-lane roundabout. Vehicles can enter the interior lane or exit from it via [Formula: see text] intersecting lane, the boundary conditions are stochastic. The traffic is controlled by a self-organized scheme. It has turned out that depending on the rules of insertion to the roundabout, five distinct traffic phases can appear, namely, free flow, congestion, maximum current, jammed and gridlock. The transition between the free flow and the gridlock is forbidden. The density profiles are used to study the traffic pattern at the interior lane of the roundabout. In order to quantify the interactions between vehicles in the interior lane of the roundabout, the velocity correlation coefficient (VCC) is also studied. Besides, the spatiotemporal diagrams corresponding to the entry/exit lanes are derived numerically. Furthermore, we have investigated the effect of displaying signal ([Formula: see text], as the [Formula: see text] decreases, the maximum current increases at the expense of the free flow and the jamming phase. Finally, we have investigated the effect of the braking probability [Formula: see text] on the interior lane of the roundabout. We have found that the increase of [Formula: see text] raises the spontaneous jam formation on the ring. Thus, enlarges the maximum current and the jamming phase while the free flow phase decreases.

Design of the First Italian Roundabout with Jointed Plain Concrete Pavement

This work presents the results of the overall design of the first Italian roundabout with jointed plain concrete pavement. The examined case study complies with current international standards and practices for geometry of roundabouts and road pavements. The construction of a concrete pavement in an urban roundabout will better manage and slow down fast vehicular flows, and increase traffic fluidity in an important junction, trafficked by heavy vehicles, where maintenance works should be reduced to avoid queues. The design of the roundabout involved several competences for: defining the geometry of the four-arm junction, designing the thickness of the jointed plain concrete pavement both on the circular crown and the arms, studying the mix design of a high resistance concrete. As regard to the pavement, the result of the study was an un-dowelled concrete pavement composed of square slabs laid on a cement concrete subbase and a granular layer. The shape of the slabs has been designed to optimize the structural performance of their material, which is a high strength concrete mix derived from an extensive laboratory test work. In general, the results summarized approaches typical of different design conditions: urban ones for traffic flow and safety needs; high-traffic ones for the chosen pavement type; airport ones for the absence of dowel and tie bars at the joints. Indeed, the article has highlighted that the design process of a concrete roundabout requires multiple analyses to consider various features and correctly re-design an existing urban junction. Its geometrical design, the structural design of the concrete pavement and the theoretical and experimental design of the concrete mix were the main phases of this process and they needed different competences to conduct comprehensive and appropriate analyses.

Unmanned Aerial Vehicle-based Traffic Analysis: A Case Study to Analyze Traffic Streams at Urban Roundabouts

Recently, multirotor Unmanned Aerial Vehicles(UAVs) or drones have become increasingly popular for a vast variety of civil applications. Efficient traffic data collection and extraction of various flow parameters are some of the futuristic applications of this technology. However, such applications still need to be streamlined and thoroughly explored for varying traffic and infrastructural conditions. In this paper, the focus is on the authentication of the application of small multirotor UAVs for traffic data collection and subsequent analysis of traffic streams at urban roundabouts. This paper presents an analytical methodology to evaluate the performance of roundabouts by extracting various parameters and performance indicators. The performance evaluation methodology is based on: (i) determining traffic volume via OD matrices for each leg, and (ii) analyzing drivers’ behavior via gap-acceptance analysis. The overall analytical process is principally based on the authors’ previously proposed automated UAV video-processing framework for the extraction of vehicle trajectories. The extracted trajectories are further employed to extract useful traffic information. The experimental data to analyse roundabout traffic flow conditions was obtained in the city of Sint-Truiden (Belgium). The results reflect the value of flexibility and bird-eye view provided by UAV videos; thereby depicting the overall applicability of the UAV-based traffic analysis system. With the significant increase in the usage of UAVs expected in the coming years, such studies could become a useful resource for practitioners as well as future researchers. The future research will mainly focus on further extensions of the UAV-based traffic applications.

Grundfos opens new manufacturing facility in India

Recently, multirotor Unmanned Aerial Vehicles(UAVs) or drones have become increasingly popular for a vast variety of civil applications. Efficient traffic data collection and extraction of various flow parameters are some of the futuristic applications of this technology. However, such applications still need to be streamlined and thoroughly explored for varying traffic and infrastructural conditions. In this paper, the focus is on the authentication of the application of small multirotor UAVs for traffic data collection and subsequent analysis of traffic streams at urban roundabouts. This paper presents an analytical methodology to evaluate the performance of roundabouts by extracting various parameters and performance indicators. The performance evaluation methodology is based on: (i) determining traffic volume via OD matrices for each leg, and (ii) analyzing drivers’ behavior via gap-acceptance analysis. The overall analytical process is principally based on the authors’ previously proposed automated UAV video-processing framework for the extraction of vehicle trajectories. The extracted trajectories are further employed to extract useful traffic information. The experimental data to analyse roundabout traffic flow conditions was obtained in the city of Sint-Truiden (Belgium). The results reflect the value of flexibility and bird-eye view provided by UAV videos; thereby depicting the overall applicability of the UAV-based traffic analysis system. With the significant increase in the usage of UAVs expected in the coming years, such studies could become a useful resource for practitioners as well as future researchers. The future research will mainly focus on further extensions of the UAV-based traffic applications.

Determining the Capacity Model of Urban Roundabouts, Considering the Drivers’ Behaviour in Accepting and Rejecting of Gaps

Nowadays, urban roundabouts are one of the most popular types of intersections that have grown highly all over the world. Thus, the accurate and engineering design of these types of intersections has a significant effect on improving their traffic performance. The capacity is one of the important traffic parameters in different intersections, which represents the maximum volume of vehicles entering the roundabouts. There are two general methods for determining the capacity of intersections including the use of analytical models such as gap acceptance model and the use of empirical methods (regression model). In the present paper, using the collected data such as entry and circulating volume, both accepted and rejected gaps were studied for three urban roundabouts and the capacity model have been determined by the use of analytical method. After implementation of the data, they became consistent and homogeneous in four different groups and the most optimized range of critical gaps as well as the follow up time were separately determined for each of these groups by using conventional methods such as Sigloch, Raff, Wu, and Harder and according to statistical analyses with a confidence level of 95%. From the obtained results, a range of 3.03 – 3.32 s for critical gap of the studied roundabouts and the range of 1.3 – 1.7 s for follow up time could be mentioned. It was used from the theory of gap acceptance in order to determine urban roundabouts capacity model, in which these gaps have a random nature and follow negative exponential distribution and by conducting this analysis (also has been used by Sigloch), some relations were obtained for determining the capacity of the roundabouts according to the impact of circulating volume and drivers’ behaviour. The results indicate that the maximum capacity of the roundabouts in the microscopic models is equal to 2400 veh/h, when the circulating flow rate is reached zero. Moreover, according to the obtained capacity model, the circulating flow never falls down to zero in the case that it reaches its peak value.

Automatic detection of traffic lights, street crossings and urban roundabouts combining outlier detection and deep learning classification techniques based on GPS traces while driving

The automatic generation of street networks is attracting the attention of research and industry communities in areas such as routable map generation. This paper presents a novel mechanism that focuses on the automatic detection of street elements such as traffic lights, street crossings and roundabouts which could be used to generate street maps and populate them with traffic influencing infrastructural elements such as traffic lights. In order to minimize the system requirements and simplify the data collection from many users with minimal impact for them, only traces of GPS data from a mobile device while driving are used. Speed and acceleration time series are derived from the GPS data. An outlier detection algorithm is used first in order to detect abnormal driving locations (which can be due to infrastructural elements or particular traffic conditions). Using deep learning, speed and acceleration patterns are automatically analyzed at each outlier in order to extract relevant features which are then classified into a traffic light, street crossing, urban roundabout or other element. The classification results are enhanced by adding the degree of atypicity for each point calculated as the percentage of times that a particular location is detected as an outlier in several drives. The proposed algorithm achieves a combined recall of 0.89 and a combined precision of 0.88 for classification.

Habitat richness and tree species richness of roundabouts: effects on site selection and the prevalence of arboreal caterpillars

This study examined the relationship between the habitat and tree species richness of roundabouts and the abundance and species richness of tree-dwelling caterpillars, and thus the potential of urban roundabouts to support breeding populations. Total tree species number on sites was related to an increase in caterpillar abundance and a greater number of habitats was associated with a higher number of caterpillar species. An increase in the total number of trees was not correlated with a greater abundance of tree-feeding Lepidoptera; nor were native trees found to support proportionally more caterpillar species than all tree species, including introduced. This could be due to differences in species accumulation, the prevalence of generalist species or a statistical sampling effect. The occupancy and average abundance of caterpillar species was generally low, which does not support the theory that Lepidoptera in urban areas tend towards mono-dominance. It may, however, represent the presence of ‘accidental’ species on roundabouts. Habitat management and planting to increase tree species diversity and density on roundabouts has the potential to increase the species diversity and abundance of arboreal Lepidoptera, and increase abundance of butterfly and moth urban populations.

Microscale traffic simulation and emission estimation in a heavily trafficked roundabout in Madrid (Spain)

This paper presents the evaluation of emissions from vehicle operations in a domain of 300m×300m covering a complex urban roundabout with high traffic density in Madrid. Micro-level simulation was successfully applied to estimate the emissions on a scale of meters. Two programs were used: i) VISSIM to simulate the traffic on the square and to compute velocity-time profiles; and ii) VERSIT+micro through ENVIVER that uses VISSIM outputs to compute the related emissions at vehicle level. Data collection was achieved by a measurement campaign obtaining empirical data of vehicle flows and traffic intensities. Twelve simulations of different traffic situations (scenarios) were conducted, representing different hours from several days in a week and the corresponding NOX and PM10 emissions were estimated. The results show a general reduction on average speeds for higher intensities due to braking-acceleration patterns that contribute to increase the average emission factor and, therefore, the total emissions in the domain, especially on weekdays. The emissions are clearly related to traffic volume, although maximum emission scenario does not correspond to the highest traffic intensity due to congestion and variations in fleet composition throughout the day. These results evidence the potential that local measures aimed at alleviating congestion may have in urban areas to reduce emissions. In general, scenario-averaged emission factors estimated with the VISSIM-VERSIT+micro modelling system fitted well those from the average-speed model COPERT, used as a preliminary validation of the results. The largest deviations between these two models occur in those scenarios with more congestion. The design and resolution of the microscale modelling system allow to reflect the impact of actual traffic conditions on driving patterns and related emissions, making it useful for the design of mitigation measures for specific traffic hot-spots.

A New Instrumented Tool for Motorcyclist Behaviour Understanding: Application to Roundabouts

Today, there are increasingly more motorcycles on the roads and the number of motorcyclists killed is greater than the number of motorists killed. The safety of powered two wheelers (PTWs) is an important issue for public authorities and road administrators. In 2014, in France, PTWs represented only 2% of traffic, but 24% of accidents and 18% of facilities. European governments have made this particular point a priority for road safety for the next decade. Yet, they are vulnerable road users for which few studies have been conducted on their behaviour and interaction with road infrastructure. Observation of their behaviour and interaction enables public authorities to understand causes in order to propose actions to improve safety for this category of road user. In this context, we developed a new tool to analyse motorcyclist behaviour in relation to road infrastructure. This tool is a motorcycle with average engine capacity. It is fitted out non-intrusive sensors so that motorcyclists can ride in real conditions. The motorcycle is equipped with multi-sensor and multi-video architectures. Both architectures are synchronised, enabling qualitative data to be paired with objectives data. Data collected includes GPS position, three axial accelerations and rotations and motorcyclist actions on the motorcycle (for example, braking, flashing, etc.). The video architecture consists of three cameras. The first observes the motorcyclist's environment. The second is positioned on the motorcyclist's helmet to observe head movements and the third films the road surface to detect lateral position and give an idea of road conditions. The objective is to obtain quantitative data to analyse motorcyclists’ dynamics in relation to road infrastructure. The tool will also help to understand interaction between different road user groups, particularly interaction between motorists and motorcyclists. Results will enable road managers to take into account the coexistent status of motorcyclists and motorists. In this study, we focus on motorcycle behaviour on urban roundabouts. Experimentation with a panel of motorcyclists was conducted. The influence zone was determined using driving parameters.

Urban and Rural Roundabout Accident Occurrence Models

PURPOSES: The operational characteristics of roundabouts are generally influenced by location as well as traffic volume. The goal of this study is to develop urban and rural roundabout accident models and to discuss safety improvement guidelines based on the model. METHODS : To analyze accidents, count data models are utilized in this study. This study used accident data from 2010 to 2013 for 56 roundabouts collected from the Traffic Accident Analysis System (TASS) of Road Traffic Authority. Poisson and negative binomial regression models were developed for this study using NLOGIT 4.0. RESULTS : The main results are as follows. First, the hypotheses that there are distributional differences in the number of accidents and injuries/fatalities among rural and urban roundabouts were accepted. Second, Poisson and negative binomial regression accident models, which were all statistically significant, were developed. Seven independent variables, which were statistically significant, were adopted. Third, the common variable of models was evaluated to be traffic volume. CONCLUSIONS : This study developed two negative binomial roundabout accident models and suggested some accident reduction strategies. The results are expected to give some implications to the safety improvement of roundabout.

Multicriteria Assessment of Crosswalk Location in Urban Roundabout Corridors

Midblock pedestrian crossing areas between closely spaced roundabouts can affect traffic operations and may result in a trade-off between capacity, environment, and safety benefits. Even though research has been conducted on the impacts of traffic performance on pedestrian crosswalks located at isolated roundabouts, few studies have focused on how pedestrian crosswalks between closely adjacent roundabouts affect traffic operations. A microsimulation approach was used to examine the integrated effect of a pedestrian crosswalk on traffic delay, carbon dioxide emissions, and relative speed between vehicles and pedestrians at different locations between closely spaced two-lane roundabouts. The main purpose of the study was to develop a simulation platform of traffic (VISSIM), emissions (vehicle-specific power), and safety (surrogate safety assessment model) to optimize such variables. The fast nondominated sorting genetic algorithm NSGA-II was mobilized to identify an optimized set of pedestrian crosswalk locations for the roundabout exit section along the midblock segment. One acceptable solution that provided a good balance between traffic performance, emissions, and pedestrian safety benefits was locating the crosswalks at 15, 20, and 30 m from the exit section. Even at low pedestrian demand, crosswalk effectiveness (as determined by capacity and environment) gradually decreased near the circulatory ring delimitation (<10 m). Findings suggest that crosswalks in the midblock segment (55 to 60 m from the exit section) also must be considered, especially under high traffic demand.