•Overall, Carmel’s roundabout program reduced injury crashes by 47%•The effects were strongest at double-teardrop roundabouts.•Double-teardrop roundabouts reduced injury crashes by 84% and total ...crashes by 63%•Single-lane roundabouts decreased 51% in total crashes and 50% in PDO crashes.•Double-teardrop roundabouts are recommended to install at interchange terminals.
Introduction: Roundabouts are a proven safety countermeasure for intersection safety. This study examined the safety effects of roundabout conversions in Carmel, Indiana, also known as the “Roundabout City.” Doing so is of particular interest because Carmel has a high density of roundabouts and its drivers understand their effectiveness and are familiar with navigating them. This study also adds to the current state of knowledge about innovative double-teardrop roundabouts (i.e., linked roundabouts with teardrop-shaped central islands). Method: Negative binomial models accounting for correlation within site pairs were applied to evaluate the safety effects of converting conventional intersections to roundabouts on total crashes, injury crashes, and property-damage-only (PDO) crashes between study sites and control sites for different roundabout types (single-lane, multi-lane, and double-teardrop). We compared crash data from a 2-year period before the installation of the roundabouts with the 2-year period after the conversions. Results: Injury crashes were 47% lower than what would have been expected without the roundabout conversions. The effects were strongest at the double-teardrop roundabouts, where injury crashes were significantly reduced by 84% and total crashes by 63%. Single-lane roundabouts experienced significant decreases of 51% in total crashes and 50% in PDO crashes (and a nonsignificant decrease of 50% in injury crashes). Multi-lane roundabouts were associated with increases in total and PDO crashes but a 15% decrease in injury crashes, though all were nonsignificant. Conclusions: Overall, the City of Carmel’s roundabout program is associated with reductions in injury crashes, which indicates improvements to safety. Single-lane and double-teardrop roundabouts are associated with improvements in the occurrence and severity of crashes. Practical Applications: Double-teardrop roundabouts should be considered for installation at interchange terminals to improve highway safety.
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Although multi-lane concentric roundabouts have a greater capacity than single-lane roundabouts, they may encourage increased driving speeds and decrease in safety. Furthermore, lane changing is ...possible in multi-lane roundabouts, thus increasing the risk of crashes. To address these drawbacks, the authors present the “Two-Geometry” Roundabout. This type of roundabout discourages lane changing within the roundabout, lowers driving speed through the roundabout, and facilitates the manoeuvres of larger and longer vehicles. The paper discusses the concept of the Two-Geometry Roundabout and outlines its principal advantages. We first delineate characteristics of single-roundabouts and multi-lane roundabouts, focusing on the problems of the latter. Next, the development, main characteristics and typologies of Two-Geometry Roundabouts are illustrated (with some examples attached); therefore, we focus on the positive effects of the Two-Geometry Roundabout with particular attention on heavy vehicles. Finally, we present methods for calculating the capacity of the Two-Geometry Roundabout and conclude the paper.
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Despite the adoption of roundabouts in developing countries for traffic management and smooth flow, the concept of traffic heterogeneity management at these intersections is relatively unexplored. ...Estimating passenger car units (PCUs) for different vehicle types to homogenize traffic is a recognized approach worldwide. In this study, vehicles were classified into five categories to provide a meaningful context for the analysis. The study proposes a model to estimate PCU values for different vehicle types, specifically at roundabouts, after identifying the potential influencing factors. The study was based on data collected from 10 roundabouts in three Indian cities, having different physical and geometrical characteristics. The proposed method yielded PCU values that were partially comparable with existing standards. Comparisons with the Indian Highway Capacity Manual (Indo-HCM) revealed that this publication underestimated PCU values for two-wheelers and three-wheelers by 20% and 11% respectively, but overestimated PCU values for big cars and heavy vehicles by 9% and 12%, respectively. Method appropriateness was ascertained from the lack of prior assumptions made about traffic and geometrical characteristics. To prevent unnecessary re-estimation of PCU values across locations, the idea of a heterogeneity counter component (HCC) was proposed. The model was trained using cross validation on a dataset of seven roundabouts, and its performance was evaluated on a separate dataset using mean absolute percentage error. The relationship between PCUs and the geometrical features of roundabouts, and the effect of traffic characteristics on HCC were studied. The findings might be considered while revising relevant codes and manuals (e.g., IRC-65:2017, Indo-HCM).
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Critical gap (CG) estimation, while taking into consideration inconsistent driver behavior resulting from heterogeneous traffic conditions, is a tedious task. Several methods dealing with CG ...estimation have been developed in the past but limited research has been done in this regard for developing countries and there is a lot of scope to explore this field considering varying traffic conditions on the roads. In this study, the maximum likelihood method (MLM), one of the most prominent methods of determining CG, has been compared with two other methods developed for traffic conditions prevailing in India. These methods use different techniques for calculating the CG, such as minimization of absolute differences of gaps given by Ahmad et al., and minimization of square root of standard deviation of actual gap value from the predicted CG as per the Indian Highway Capacity Manual (Indo-HCM). This paper discusses the estimation of CG for five different categories of vehicles using these methods to counter the heterogeneity of traffic. Data has been collected on two urban multi-lane roundabouts in India. SOLVER in MS Excel is used to optimize the functions defined in all three methods. The results reveal that the method suggested by Ahmad et al. gives the most consistent results which are close to actual value when driver behavior is inconsistent. The other two methods are also reasonably consistent, with the method given in Indo-HCM being slightly better than MLM. Further, two-way ANOVA was applied to check the consistency of results.
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•The dilemma zone at roundabouts and driving factors that affect the stop/go decision was studied.•The DZ is shorter and closer to stop-line, as compared to signalized intersections.•Driver reaction ...time match to a large extent with the values mentioned by AASHTO and ITE.•Acceleration and deceleration rates are not similar to those values proposed by AASHTO and ITE.•Drivers drive more conservatively at roundabouts and are more willing to stop.
In some Asian countries, roundabouts were designed as a tool for landscape and urban planning in less-populated areas, which did not initially need traffic lights. However, as the urbanization grew, it was needed to signalize these roundabouts to prevent accidents. One of the main reasons for high accident rates at intersections is the dilemma that drivers face when the signal changes from green to yellow. The purpose of this paper is to study the dilemma zone (DZ) at roundabouts and driving factors that affect the stop or go decision. This paper determines the length of all-red interval for yellow light running (YLR) vehicles, using time to collision (TTC) and kinematic motion (KM) methods. TTC sets all-red interval so that the “last to go” vehicles have enough time to clear middle of the roundabout before conflicting vehicles reach the conflict point. KM method applies the kinematic motion equations to estimate the time required to clear the conflict point. The obtained results for three roundabouts in Mashhad, Iran demonstrate that the DZ is shorter and closer to stop-line, as compared to signalized intersections. Drivers drive more conservatively at roundabouts and are more willing to stop. Comparison of TTC and KM reveals that the central tendency and dispersion measures of all-red interval are larger in disaggregate KM method. Studying driving factors shows that driver perception-reaction time of drivers at roundabouts matches to a large extent with the values recommended by AASHTO and ITE. However, such consistency is not observed for acceleration and deceleration rates.
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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.
A path planning and control approach of a non-holonomic three-wheeled mobile robot (WMR) for online navigation in road following and roundabout environments is presented in this paper. We proposed a ...complete navigation algorithm that enables the WMR to autonomously navigate on the road with various scenarios. With such an algorithm, the robot is able to localize itself within the road environment and find a collision free-path starting from a pre-defined start position to a goal point using a novel approach called laser simulator (LS). The path planning and roundabout detection are determined based on LS and sensor fusion of a laser range finder, camera, and odometry measurements. The sensor fusion algorithm is used to remove noises and uncertainties from sensors' data and provide optimum measurements for path planning. A robot motion control scheme is used for the purpose of controlling the kinematic parameters of WMR using a resolved acceleration control coupled with an active force control for rejecting the disturbances. Experimental results show the capability of the proposed algorithms to robustly drive the robot on the road following and roundabout environments.
Transport is one of the essential elements of critical infrastructure. It is necessary to solve the traffic jam problem and threaten life, health, and property. However, there are several places ...where these problems are. There is required to solve this problem. One of them is in the selected village in the Zlín Region, Czech Republic. There are two problem places where are frequently the accident. This paper aims to introduce this intersection and prepare the optimized. The paper is divided into few parts. Firstly, there will be a literature review in traffic and the implementation into the critical infrastructure. Secondly, there will be introduced the methods which will be used for this research. Next, there will be the central part of the paper – results. The results are suitable for supplementation with the figures. These figures will represent the current state of the traffic in the village and others with the problem places. The second part of the results will describe the optimized traffic situation by using roundabouts.
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There is considerable evidence that roundabouts are the safest and most efficient form of traffic control for most intersections. The potential use of roundabouts with all their inherent benefits may ...be greatly diminished if they are not able to accommodate oversize/overweight (OSOW) vehicles, sometimes called “Superloads.” The problem, therefore, is how to accommodate OSOW vehicles without sacrificing the integrity, safety and other benefits of roundabouts.
This study uses TORUS software to design six standard roundabouts using guidance from the latest Federal Highway Administration (FHWA) roundabout guide. Six OSOW check vehicles from the Wisconsin Department of Transportation’s library were used to modify the designs to accommodate these selected check vehicles at the roundabouts. These six OSOW check vehicles were used to conduct swept path analysis using AutoTURN software at the selected six standard roundabouts for right turn, through, and left turn simulations. The space requirements for these maneuvers were analyzed in detail. Various strategies for better accommodating these OSOW check vehicles were suggested and experimented with in this study using AutoTURN software simulations. The effectiveness of using a straight passage through the center island for OSOW vehicles was also addressed in this study and was found to be effective. All the strategies investigated in this study proved to be effective in accommodating OSOW vehicles when compared to conventional ways of using a roundabout. The needed total truck apron was calculated and used as a reference to determine an effective strategy for accommodating OSOW vehicles. This research can be used as guidance for transportation engineers, planners and decision makers to determine possible ways of designing a roundabout at an intersection where certain OSOW vehicles are expected.
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