Many roundabout capacity models are present in the world and they are classified into three key groups: empirical models, theoretical models, and microscopic simulation models. In Bosnia and ...Herzegovina and the Republic of Croatia, there is no roundabout capacity model prescribed by a rulebook. Theoretical capacity models are derived from gap acceptance theory. Due to some deficiencies of gap acceptance theory, Brilon and Wu introduce a new concept for analyzing the capacity of unsignalized intersections, and thereby of roundabouts too, based on conflict theory and queuing theory. This paper analyzes three roundabout capacity models most commonly used in the world (HCM, Akcelik, Brilon-Wu), with different theoretical backgrounds, in order to compare them with directly measured capacity in the field in local conditions in Bosnia and Herzegovina and thus to see the differences in application results.
The increasing congestion on transportation networks has raised inconvenience among the network’s users, especially in major cities intersections where there are frequently problems experienced like ...delays and low levels of service. Roundabouts are always offered as a solution or an alternative from existing signalized intersections believing in their substantial delays reduction. However, it is essential to adopt advanced transportation analysis tools to ensure whether this solution performance would last overtime or not. This study focuses on evaluating the performance of two real existing roundabouts in Jeddah and Al-Madinah cities over time. It aims at analyzing and assessing the level of service of these two intersections in the case of existing roundabouts and their parallel solution of signalized intersections to decide when it is better to convert the existing roundabout into a signalized intersection. Sidra and Synchro, as the simulation tools are fed with synthetically generated demand scenarios, represent the normal increase in traffic with passing years. As a result, the underperforming year is easily detected for both intersections. Also, the impact of the rise in left-turn volume is evaluated for both solution types. It is expected that the proposed framework would help practitioners to continuously assess the applicability of converting roundabout solutions to signalized intersections besides determining the span of service.
•Type of intersection influences the noise level in its vicinity.•Traffic volume, composition and management on intersections decide on noise level.•Varied noise levels were observed near different ...entries of signalized roundabouts.
The analysis, assessment and estimation of noise levels in the vicinity of intersections is a more complex problem than a similar analysis for roads and streets. This is due to the varied geometry of the intersections, differences in the loads of individual movements, participation of heavy vehicles and mass transport vehicles, as well as the various types of traffic management and traffic control. This article analyses the influence of intersection type and traffic characteristics on the noise levels in the vicinity of classic channelized intersections with signalization, roundabouts and signalized roundabouts. Based on the conducted measurements, it has been established that, with comparable traffic parameters and the same distance from the geometric centre of the intersection, the LAeq value for signalized roundabouts is 2.5–10.8dB higher in comparison to classic channelized intersections with signalization and 3.3–6.7dB higher in relations to the analysed roundabout. Additionally the differences between LAeq levels at individual entries at the same signalized roundabouts may reach the value of approximately 4.5dB. Such situation is influenced by differences in the intersection geometry, diameter of the intersection’s central island, traffic flow type, traffic management at the entries and traffic volume, especially the amount and traffic movements of multiple axle heavy vehicles. These factors have been analysed in detail in relation to signalized roundabouts in this paper.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The authors have already developed and studied the Two-Geometry Roundabouts in terms of design principles. This paper in fact is the natural extension a previous article by Pratelli et al., 2022, in ...which the authors discussed the main concepts of the Two-Geometry Roundabouts and the details that determine their success. However, when someone talks about roundabouts in general, it is also essential to specify which respective capacity model is most suitable. The Highway Capacity Manual (HCM6th) provides a popular method for estimating the capacity of conventional roundabouts. Nevertheless, the Two-Geometry Roundabouts are classified as unconventional roundabouts, and therefore this paper aims to answer the following crucial question: “Which capacity model should be used to calculate a Two-Geometry Roundabout?”. Firstly, the impositions of the Italian guidelines, where all roundabouts with a non-circular shape or with an inscribed diameter greater than 50 meters are defined as unconventional, are described. The achieved empirical results in respect to some test has compared with those otherwise obtained through the HCM6th methodology. Next, two popular methods suitable for calculating the capacity of Two-Geometry Roundabouts are resumed, namely the SETRA method and the Brilon-Wu method. These two are chosen because on the one hand SETRA directly requests dimensions of some selected geometric components; while on the other hand, the Brilon-Wu approach is based only on a few macro characteristics such as the number of entry/circulation lanes and the values of the gap acceptance parameters. Then, the successive section is devoted to comparing performance between a Traditional circular Roundabout and a Two-Geometry Roundabout, designed for the same intersection. This comparison was carried out through the use of experimental results obtained with a dynamic simulation approach made with Aimsun software. Finally, the paper ends with a brief discussion on some possible insights framed in a further development of the research, which could involve the safety models of Two-Geometry roundabouts, and their possible extension to roundabout corridors.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Urban agglomerations close to road infrastructure are particularly exposed to harmful exhaust emissions from motor vehicles and this problem is exacerbated at road intersections. Roundabouts are one ...of the most popular intersection designs in recent years, making traffic flow smoother and safer, but especially at peak times they are subject to numerous stop-and-go operations by vehicles, which increase the dispersion of emissions with high particulate matter rates. The study focused on a specific area of the city of Rzeszow in Poland. This country is characterized by the current composition of vehicle fleets connected to combustion engine vehicles. The measurement of the concentration of particulate matter (PM2.5 and PM10) by means of a preliminary survey campaign in the vicinity of the intersection made it possible to assess the impact of vehicle traffic on the dispersion of pollutants in the air. The present report presents some strategies to be implemented in the examined area considering a comparison of current and project scenarios characterized both by a modification of the road geometry (through the introduction of a turbo roundabout) and the composition of the vehicular flow with the forthcoming diffusion of electric vehicles. The study presents an exemplified methodology for comparing scenarios aimed at optimizing strategic choices for the local administration and also shows the benefits of an increased electric fleet. By processing the data with specific tools and comparing the scenarios, it was found that a conversion of 25% of the motor vehicles to electric vehicles in the current fleet has reduced the concentration of PM10 by about 30% along the ring road, has led to a significant reduction in the length of particulate concentration of the motorway, and it has also led to a significant reduction in the length of the particulate concentration for the access roads to the intersection.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
With more than 460 roundabouts located in Abu Dhabi, the capital city of the United Arab Emirates, it is imperative to evaluate the safety benefits provided by those roundabouts. In this study, two ...approaches were used to evaluate those safety benefits. The first approach is by measuring the 85th percentile operating speeds at a sample of 18 roundabouts in Abu Dhabi to determine whether the measured operating speeds conform to what is recommended by design guides. The second approach is by using a questionnaire to measure how drivers in Abu Dhabi perceive safety when driving at roundabouts and to measure their level of knowledge regarding the rules pertaining to driving at roundabouts. The study found that operating speeds at Abu Dhabi roundabouts typically exceed those recommended by design guides. The study also found that only 4.1% of the drivers interviewed demonstrated a comprehensive understanding of the rules pertaining to driving at roundabouts. Ordinal regression modeling was used to identify driver groups in need for more awareness of the rules to negotiate roundabouts in Abu Dhabi. The study found that the driver group in most need for more awareness is typically young and middle-age male drivers (below the age of 46 years) with less driving experience in countries where roundabouts are common. The questionnaire also revealed that despite the operational benefits provided by roundabouts (in terms of reduced delay), drivers do not prefer to drive at Abu Dhabi roundabouts, which might be explained by drivers' perception of Abu Dhabi roundabouts being not safe.
•Operating speeds were measured at Abu Dhabi roundabouts using radar guns.•Operating speeds at Abu Dhabi roundabouts were found to be excessive.•Most drivers have inadequate knowledge related to driving at roundabouts.•Male drivers below 46 years need better education on driving at roundabouts.•20.5% of drivers feel safer at roundabouts than at signalized intersections.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Replaces single-lane by turbo-roundabout and yield- and Stop-controlled RCUT.•Collects traffic, pedestrian, and cyclist data from two single-lane roundabouts.•Uses microscopic models to assess ...traffic performance, emissions and driving volatility.•Turbo-roundabout generally yields the lowest travel times and CO2 and NOx emissions.•Yield-RCUT is the best option concerning idling times, queues, and speed indicators.
This research explored the potential of replacing conventional single-lane roundabouts by turbo-roundabouts and yield- and stop-controlled restricted crossing U-Turn (RCUT) at intersections located in urban corridors. A simulation approach based on a well-integrated assessment of traffic performance, emissions and driving volatility indicators of alternative intersection designs (AIDs) is therefore a major contribution of the study. The paper also addressed the impacts that several locations of the U-Turn crossovers have on travel and idling times, as well as on carbon dioxide and nitrogen oxides emissions. Traffic, pedestrian, and cyclist flow data were collected from two urban three-leg single-lane roundabouts. A microscopic simulation platform of traffic and emissions (respectively, VISSIM and vehicle specific power) was used to evaluate intersection-specific design and operations. The results indicated that turbo-roundabout and yield-controlled RCUT outperformed the existing single-lane roundabout at the two sites. Turbo-roundabout generally yielded the lowest travel times and emissions compared to the other intersections. The Yield-RCUT also performed better than the single-lane roundabout for U-Turn crossover located 100–170 m from the main intersection. Our findings bring a solid basis for academic research and transportation planners to promptly consider the implementation of AIDs and contribute to sustainable mobility in cities.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
