A growing number of studies, presented in scientific and professional literature, point out a poor traffic safety characteristic of "standard" two-lane roundabouts, and lower capacity than expected. ...These problems are resolved in different ways in different countries; however, the most successful solution has proven to be reducing the number of conflict points. Lower number of conflict points is one of the characteristics of alternative (or unconventional or no-widespread) types of roundabouts. Alternative types of roundabout differ from "standard" two-lane roundabouts in one (or more) design elements, while the purpose of their implementation is also specific. This paper illustrates two established alternative types of roundabouts (turbo and flower roundabout), and two alternative types of roundabouts in development phase (reduced-turbo and semi-turbo roundabout), offering their detailed functional description, and comparison of their capacity and traffic safety characteristics. Comparative analyses of turbo, reduced-turbo, flower and semi-turbo roundabouts was made by evaluation approach based on simulation of traffic operating at four types of alternative design layouts, including exact geometric layout of the traffic site and the precise representation of traffic flows, with turning movements, through origin-destination matrixes. The capacity comparison was conducted by a software tool VISSIM, while the traffic safety comparison was made by a software tool SSAM. In traffic safety analyses, microsimulation was used to simulate traffic operations at various levels of traffic volume. Performance measures were obtained, including measures of traffic safety, based on conflicts estimated from trajectories generated in microsimulation. According to the results, level of traffic safety (as well as capacity) of analysed alternative types of roundabouts depends on traffic flow strength, and on numbers of right-hand and left-hand turning vehicles. Consequently, for different circumstances, there are different optimal alternative types of roundabouts.
The paper by R. Lattarulo et al. developed a complete framework of motion planning for automated vehicles while considering different constraints with parametric curves for lateral and longitudinal ...planners. A generalized linear model framework was used to estimate the prediction model based on field collected crash data for 26 roundabouts. More in particular, the prototypic approach is adopted from the aircraft airworthiness support measures concepts of developed from subjective analysis on the basis of Jaynes’ principle in the framework of the calculus of variations theory.
The efficacy of the application of traffic models depends on a successful process of model calibration. Microsimulation models have a significant number of input parameters that can be optimized in ...the calibration process. This paper presents the optimization of input parameters that are difficult to measure or unmeasurable in real traffic conditions and includes parameters of the driver’s behavior and parameters of Wiedemann’s psychophysical car-following model. Using neural networks, models were generated for predicting travel time and queue parameters and were used in the model calibration procedure. This paper presents the results of a comparison of five different applications of neural networks in calibrating the microsimulation model. The VISSIM microsimulation traffic model was selected for calibration and field measurements were carried out on two roundabouts in a local urban transport network. The applicability of neural networks in the process of calibrating the microsimulation models was confirmed by comparison of the modelled and measured data of traffic indicators in real traffic conditions. Methods of calibration were validated with two sets of new measured data at the same intersection where the calibration of the model was carried out. The third validation was made at the intersection in a different location. The selection of the optimal calibration methodology is based on the model accuracy between the simulated and measured data of traveling time, as well as queue parameters. The microsimulation model provides access to the raw data of observed traffic parameters for each vehicle in the simulation. The dataset of the calibrated model simulation results of all travel times of the selected traffic flow was compared with the dataset of the measured field data to determine whether the data are statistically significantly different or not.
Alternative types of roundabouts are usually more recent and have been implemented only in certain countries. Typically, they differ from “standard” roundabouts in one or more design elements, whilst ...the purposes of their implementations are also specific. The main reasons for their implementations are particular the disadvantages of “standard” one- or two-lane roundabouts in particular circumstances or changes of “actual circumstances” which in the past has led to roundabout implementations. Today, several different types of roundabouts are well-known (“mini”, “double mini”, “dumb – bell”, “with transition central island”, “with joint splitter islands”, “traffic signal controlled”, “assembled roundabouts” …), and it is possible to stipulate that they will be further developed in the future. This paper illustrates two relative new alternative types of roundabouts – “turbo” and “flower” roundabouts and their comparison from design, traffic safety and capacity point of view.
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
The problems of low level traffic safety on multi-lane roundabouts have been resolved in various ways in different countries, usually by using alternative types of roundabouts that reduce the number ...of conflict points. Alternative types of roundabouts typically differ from 'normal' or 'standard' roundabouts in one or more design elements, as their implementation purposes could also be specific. Today, several different types of roundabouts are already in use ('mini', 'double mini', 'dumb-bell', those 'with joint splitter islands' ('dog-bone'), those 'with a spiralling circular carriageway' ('turbo'), those 'with depressed lanes for right-hand turners' ('flower') etc.). This paper introduces a new type of roundabout, dual one-lane roundabouts on two levels with right-hand turning bypasses, namely the 'target roundabout'. This paper describes and analyses their design, traffic safety, and capacity characteristics, compared with the standard two–lane roundabouts.
Motorcycle riders are an increasing group of road users. The intrinsic characteristics of powered two wheelers (PTW) allow them to be particularly flexible, both in urban and extra-urban ...environments. Nevertheless, crash statistics indicate that riders involved in road accidents are highly likely to suffer severe injuries, underlining the vulnerability of this group of road users. An element that can greatly affect the safety of PTW users is road design, as roads are usually designed for two-track vehicles (cars, buses, and lorries) and do not consider the needs of PTWs. Additionally, handling a motorcycle is quite different from driving a car; thus, the behaviour of riders is different to that of drivers. The aim of this paper is to compare how different road designs are perceived by riders and drivers and to preliminarily assess if riders’ behaviour and attention allocation are related. For the purpose of this research, an eye-tracking experiment was developed outdoors. Both drivers and riders travelled along a route comprising four different road designs and various road layouts, and the output was analysed both qualitatively and quantitatively. Although it was not possible to carry out a statistical analysis due to the limited number of participants, the results demonstrate that there is a difference in the gaze behaviour of drivers and riders, with the latter being far more focused on the left-hand side of the road and concentrating on defined elements of road design. Furthermore, the experiment demonstrated that a higher number of fixations is related to lower speeds. Finally, it was noted that both kinds of road users focus fairly well on the carriageway, leading to the conclusion that the indications given through road markings may be much more effective than vertical signalisation, which has rarely been observed.
The number of elderly people is increasing worldwide, especially in Europe. Such an aging of the population has numerous consequences for society, many of which relate to transportation: older ...people, aware of their reduced abilities, prefer walking to driving. This leads to an increase in the elderly walking population and thus the need to understand and address the safety issues of these road users. Although these issues are well known, this topic has been little researched so far. The objective of this research is to provide a deeper insight into the safety level of elderly pedestrians by recognizing repetitive patterns leading to accidents involving them, to highlight the magnitude of the problem by analyzing a 10-year pedestrian crash database, to develop a model predicting—on the basis of the recognized patterns—the severity level of collisions involving older pedestrians, and, finally, on the basis of the highlighted factors, to propose some countermeasures to improve their safety. In order to achieve this goal, first, a statistical analysis of the database is performed, considering 13 factors that lead to accidents. Second, Kolmogorov–Smirnov and Anderson–Darling tests are performed to check if the data follow a normal distribution. Finally, an ordinal logistic regression model is proposed to determine the relationship between the crash severity level and the factors characterizing collisions. Thanks to this model, the statistical influencing factors are highlighted. Finally, based on the previous analysis, some technical and educational countermeasures are proposed.
•To apply traffic simulation model in local conditions, it is necessary to calibrate the model.•A new calibration method by using computer software was analyzed..•A neural network is applicable in ...the process of calibration of the micro-simulation model.•VISSIM micro-simulation model is used for calibration done at the example of urban roundabouts..•The calibration method is applicable in the VISSIM as well as in other micro-simulation models.
This paper presents the results of research on the applicability of neural networks in the process of computer calibration of a microsimulation traffic model. VISSIM microsimulation model is used for calibration done at the example of roundabouts in an urban area. The calibration method is based on the prediction of a neural network for one traffic indicator, i.e. for the traveling time between measuring points. Besides the traveling time, the calibration process further/also involves a comparison between the modeled and measured queue parameters at the entrance to the intersection. The process of validation includes an analysis of traveling time and queue parameters on new sets of data gathered both at the modeled and at a new roundabout. A comparison of the traffic indicators measured in the field and those simulated with the calibrated and uncalibrated microsimulation traffic model provides an insight into the performance of the calibration procedure.
Over recent decades, roundabouts have become increasingly used when building new at-grade intersections or up-grade junctions all over the world. Consequently, control of traffic flows at at-grade ...intersections and up-grade junctions using roundabouts creates unique design problems. Nowadays, ‘alternative’ types of roundabouts have started to become very popular, especially because of their advantages compared with ‘standard’ roundabouts and standard types of up-grade junctions. Some of these alternative types of roundabouts are two-level roundabouts, which are still currently in the development phase. It is for this reason that they can be called ‘theoretical roundabouts’. Two-level roundabouts are particularly useful in urban and suburban areas with space limitations due to their relatively small footprint. This paper illustrates three new alternative types of two-level roundabouts—‘target’, ‘four flyover’, and ‘roundabout with left and right bypasses’—as well as their functions, capacities, and traffic safety characteristics.
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