Urban Roundabouts Research Articles

Development of Safety Performance Measures for Urban Roundabouts in India

Roundabouts, although considered as safe among the various intersection types, have seen an increasing crash rate over the years in India. Geometric design of a roundabout directly influences the driver’s speed adoption and maneuvering behavior, and hence plays a vital role in its safety performance. Application of treatments at roundabouts by altering the geometric design requires careful safety evaluation before actual implementation. The present study identified the crash causes and devised safety performance measures for urban roundabouts located in the state of Kerala, India. Crash prediction models and crash modification factors (CMFs) are developed in this study for the safety assessment of geometric design features of roundabouts. Of the many models tried, the zero-inflated negative binomial regression model is the best model to predict the crash frequency of roundabout approaches. Geometric features of the central island, circulatory roadway, and approach roads are associated with the crash occurrence on roundabout approaches. CMFs are developed by a cross-sectional method and are useful for investigating the relationship between safety and geometric design features of roundabouts.

A Cellular Automaton Model for Heterogeneous and Incosistent Driver Behavior in Urban Traffic

In this paper a cellular automaton model is proposed to describe driver behavior at a single-lane urban roundabout. Driver behavior has been considered as heterogeneous and inconsistent. Most traffic papers in the literature just discussed heterogeneous driver behavior, to our best knowledge. Two truncated Gaussian distributions are used to model heterogeneous and inconsistent driver behavior, respectively. The physical meanings of two truncated distributions are indicated. This method may help enhance a better understanding of driver behavior at roundabout traffic, and even possibly provide references for roundabout design and management.

Urban Road Roundabout Method of Contrast Optimization and Research

Taking the unconventional roundabout of Huancheng West Road and Huancheng North Road in Jinhua City an example, a research about the existing roundabout is carried on. Through the project’s development, some problems have been discovered, and we put forward some optimized measures for the unconventional roundabout by way of keeping headway exactly. In addition, we optimize the object of study by utilizing the VISSIM software, with which the traffic capacity of roundabout is to develop. Afterwards, a conclusion is drawn that if the vehicles keep the time headway of 0.6S, the traffic capacity of roundabout will be four times as large as it was, with which a new way of thinking about optimizing the roundabout will be provided.

Identifying crash contributory factors at urban roundabouts and using association rules to explore their relationships to different crash types

The use of roundabouts improves intersection safety by eliminating or altering conflict types, reducing crash severity, and causing drivers to reduce speeds. However, roundabout performances can degrade if precautions are not taken during either the design or the operation phase. Therefore, additional information on the safety of the roundabouts is extremely helpful for planners and designers in identifying existing deficiencies and in refining the design criteria currently being used. The aim of the paper was to investigate the crash contributory factors in 15 urban roundabouts located in Italy and to study the interdependences between these factors. The crash data refer to the period 2003–2008. The identification of the crash contributory factors was based on site inspections and rigorous analyses performed by a team of specialists with a relevant road safety engineering background. Each roundabout was inspected once every year from 2004 to 2009, both in daytime and in nighttime. Overall, 62 different contributory factors and 2156 total contributory factors were identified. In 51 crashes, a single contributory factor was found, whereas in the other 223 crashes, a combination of contributory factors was identified. Given the large amount of data, the interdependences between the contributory factors and between the contributory factors and the different crash types were explored by an association discovery. Association discovery is the identification of sets of items (i.e., crash contributory factors and crash types in our study) that occur together in a given event (i.e., a crash in our study). The rules were filtered by support, confidence, and lift. As a result, 112 association rules were discovered. Overall, numerous contributory factors related to the road and environment deficiencies but not related to the road user or to the vehicle were identified. The most important factors related to geometric design were the radius of deflection and the deviation angle. In existing roundabouts, the improvement of these factors might be quite expensive, but the crucial role of a moderate radius of deflection and a large deviation angle in the design of new roundabouts was stressed. Many of the contributory factors were related to markings and signs, and these factors could be easily removed with low-cost safety measures. Furthermore, because of the association between the markings, signs, and geometric design contributory factors, the study results suggest that the improvement in markings and signs might also have a significant effect in the sites where geometric design deficiencies were identified as contributory factors.

Comparison of Safety Performance Models for Urban Roundabouts in Italy and Other Countries

In Italy, almost half of all road crashes occur at intersections, primarily in urban areas. In recent years the widespread conversion of at-grade intersections to roundabouts has brought many safety advantages. To assess the safety benefits of roundabouts, transportation professionals need the powerful statistical tool known as the safety performance function (SPF). To date there has been no reported application of this tool to assess the relative safety performance of Italian urban roundabouts. This paper fills that void by using data sets from two municipalities in northern Italy. SPFs were estimated for each city with the negative binomial error distribution and then recalibrated for application in the other city by using the procedure described in the Highway Safety Manual. Model reliability and between-city transferability were evaluated with the cumulative residuals method. To assess how the Italian roundabout SPFs might be used to learn lessons from differences in crash experience for similar intersections elsewhere, a comparison with models from other countries is also provided. This comparison reveals that Italian roundabouts tend to be less safe. Potential reasons for this finding are explored.

LEDVILLE Project : Traffic Roundabout LED Lighting System.

We report a global study of a LED lighting system for an urban roundabout (LED-VILLE). A study of the photometric performances of the LED used has been performed in our laboratory. Furthermore, average illuminance, uniformity and luminance have been measured and compared to recommended data. Environmental footprints of this lighting system (carbon operation, life cycle analysis and light pollution) has been evaluated and compared to equivalent solution widely used to date. Finally, a social approach of the LED street lighting has been achieved: the visual perception felt by driving or walking users through the roundabout have been collected and analyzed.

Comparing Safety Performance Measures Obtained from Video Capture Data

Safety performance is evaluated by using measures obtained experimentally from a videotaping of traffic operations at an urban roundabout situated in Cosenza, Italy. Five different expressions of safety performance from the perspective of “rear-end” vehicle interactions include maximum deceleration rate to avoid a crash (DRAC), time-to-collision (TTC), proportion of stopping distance (PSD), time integrated time-to-collision (TIT), and crash potential index (CPI). Differences in safety performance are discussed with respect to the type of measure, traffic conditions, and variations in roundabout geometry. The results of this analysis suggest that safety performance is highly sensitive to the way it is measured; different measures can highlight different locations or geometric features of the roundabout as posing potential safety problems. This study underscores the usefulness of safety performance measures for providing meaningful experimental indicators of potential safety problems at roundabouts and how ...

Multimodal Accessibility of Modern Roundabouts

Modern roundabouts have become popular in North America during the past decade. This popularity can be attributed to their great success in Europe and Australia. There has been significant debate, however, over their accessibility for pedestrians. With almost uninterrupted traffic flows, roundabouts make it difficult for the visually impaired to determine safe gaps, as they rely on auditory cues alone. Such crossing is particularly complicated by ambient noises and circulating vehicles on busy urban roundabouts. Various pedestrian signals have been installed at roundabouts overseas. The United States Access Board published a draft guideline proposing pedestrian signals at all roundabout crossings to ensure access for the visually impaired. Roundabout operations can be a complex process of transporting multimodal travelers. There is increased interest in harnessing artificial intelligence to address issues to improve transportation systems. This research developed a crosswalk signal and introduced fuzzy logic control (FLC) into the signal timing to accommodate roundabout users. The system was assessed against the Pedestrian User-Friendly Intelligent (PUFFIN) crossings under varied geometries under different traffic conditions. The objective was to identify potential treatments for improving roundabout accessibility, safety, and efficiency. The results reveal that “distant” layout reduces vehicle delays and queue lengths when the FLC signal is applied, especially under saturated traffic conditions. From safety and operational perspectives, the FLC signal outperforms PUFFIN. The FLC signal implements the signal timing effectively, decreases pedestrian delay, and maintains adequate vehicle circulation. Multimodal traveler needs at a modern roundabout are satisfied in manifold ways.

Speed reduction effects of urban roundabouts

Road safety is one of the most serious problems in road traffic in many countries, including the Baltic countries. One of the alarming issues in road safety is the safety on urban crossings. As the number of intersections is still in a very bad and unsafe shape, there is a big need to reconstruct these intersections in a modern way. Roundabouts are coming more and more popular in many countries of the world, and often they are considered to be as one of the basic intersection types in urban areas. In Estonia, as in most European countries, roundabouts have steadily become more and more popular during the last years especially because of the foreign experience – showing the excellent accident records, traffic performance, and traffic calming properties. But still some doubts have been encountered in Estonia regarding potential capacity restrictions, traffic restrictions for big trucks and buses and sometimes with traffic safety treatments for bicyclists, pedestrians and the disabled. No overall statistics regarding the present number, growth rate, and design of roundabouts in Estonia are available. The goal of this paper was to find which factors could affect the drivers’ speed choice at roundabouts. By the of obtained data we can follow up, that the main factor influencing the drivers’ speed choice is an inscribed circle diameter of the roundabout.

Crash Analysis of Roundabouts at High-Speed Rural Intersections

Federal, state, and local agencies have identified increased intersection safety as an achievable objective in their campaigns for safer highways. Roundabouts could reduce the number of fatal and severe crashes. Roundabouts have been successful in Europe and Australia in both urban and rural environments for decades. The documented safety benefits associated with roundabouts address numerous concerns surrounding injury crashes at intersections; however, applications of roundabouts on two-lane, high-speed (40+ mph) rural highways have not been explored to the extent that urban roundabouts have in the United States. This research conducted a safety analysis of 17 intersections on high-speed rural roadways in the United States that were converted to roundabouts. The findings show the average injury crash frequency was reduced by 84%, average injury crash rate was reduced by 89%, angle crashes were reduced by 86%, and fatal crashes were reduced by 100%.

Driver's Critical Gap Calibration at Urban Roundabouts: A Case Study in China

Roundabouts have been used successfully in cities throughout the world and are wildly used in China. The critical gap is a required parameter for calculating the capacity of roundabouts and deciding the needs for stop signs. While many studies on gap acceptance characteristics at roundabouts have been carried out in America and Europe, few have been done in China. This study was conducted to calibrate the critical gap in a roundabout in China. The differences between critical gaps on different days (workdays and weekends) and during different times (rush hour and non rush hour) were checked. The study was performed at a three-lane roundabout formed by a two-way and four-lane local road and a six-lane divided artery. The data was collected at this site by a video camera. The evaluations included the cumulative probability distributions of the acceptable and rejected gaps which resulted in critical gaps for all cases. The results show that the critical gap during the rush hour is shorter than after the rush hour, but the difference is not large and the cumulative probability distributions can be fit by the logit functional form with parameters estimated using linear regression.

Roundabout In-Service Safety Reviews

The number of roundabout intersections is quickly increasing around the world, mainly because of their good safety performance. However, roundabout performance can be degraded if precautions are not taken during either the design or the operation phase. Safety review methodologies are well suited for roundabout analysis, but their effectiveness can be improved substantially if the review recommendations are supported by a quantitative safety assessment. A roundabout safety assessment procedure is presented. Validation of the safety assessment procedure was carried out by a comparison of the results with empirical Bayes (EB) safety estimates. From the procedure, a safety index (SI) for roundabout approaches and for the whole number of roundabouts is assessed. The SI was assessed for 55 approaches of 15 urban roundabouts in Italy. For approaches, the correlation between the SI values and the EB safety estimates is highly significant (t = 15.62, p-value < 0.001), with 83% of the variation in the estimated number of crashes explained by the SI value. For all roundabouts, the correlation between SI values and EB safety estimates remains highly significant (t = 14.27, p-value < 0.001), with 94% of the variation in the estimated number of crashes explained by the SI value. The SI procedure makes it possible to support review recommendations by a quantitative safety evaluation. The SI can be used to rank both roundabouts and roundabout approaches by priority according to potential crash reduction from the safety measures. Furthermore, the SI procedure allows detection of safety issues that contribute the most to safety problems.

MODELLING TRAFFIC FLOW AT MULTI-LANE URBAN ROUNDABOUTS

This paper proposes Multi-stream Minimum Acceptable Space (MMAS) Cellular Automata (CA) models to study unsignalised multi-lane (two- or three-lane) urban roundabouts. Through detailed space considerations, using Cellular Automata (CA) and the Multi-stream Minimum Acceptable Space method, heterogeneity and inconsistency of driver behavior and interactions in cross traffic at entrances of roundabouts are simulated by incorporation of four different categories of driver behavior (i.e., conservative, moderate, urgent and radical), together with reassignment of categories with given probabilities at each time step. The method is able to reproduce many features of urban traffic, for which gap-acceptance models are not robust. Multi-lane roundabout models, in particular for two-lane roundabouts, are developed with different vehicle lane-allocation patterns. Various properties of multi-lane roundabout operations have been explored including throughput, turning rates, critical arrival rates and congestion. The operations of two- and three-lane roundabouts are compared in terms of throughputs. Vehicle movements in this paper relate to left-side driving, such as found in Ireland, New Zealand and the UK. However, results are generally applicable to the countries where the give-way rule is applied.

Street Crossing by Sighted and Blind Pedestrians at a Modern Roundabout

Pedestrian behavior and safety at roundabouts are not well understood, particularly for pedestrians with sensory or mobility impairments. A previous study in which participants indicated when they would cross suggested that blind pedestrians miss more crossing opportunities and make riskier judgments than sighted pedestrians. The present study replicated these findings and analyzed actual street crossings. Six blind and six sighted pedestrians negotiated a double-lane urban roundabout under high and low traffic volumes. Blind participants waited three times longer to cross than sighted participants. About 6% of the blind participants' crossing attempts were judged dangerous enough to require intervention, compared to none for sighted pedestrians. Drivers yielded frequently on the entry lanes but not the exit lanes. Sighted participants accepted drivers' yields, whereas blind participants rarely did so. Blind-sighted differences are interpreted in terms of auditory access to information about traffic, and policy implications are discussed regarding accessibility of transportation systems.

Biodiversity on urban roundabouts—Hemiptera, management and the species–area relationship

Summary The biodiversity of insects within urban areas has been relatively little studied. Given the large and ever increasing extent of urban areas, and that the insect species richness there can be high, it is important to know the factors determining that aspect of biodiversity. In this study two of these factors, namely habitat management and area, were considered. Arboreal and grassland Hemiptera, and grassland plants, were sampled on 18 roundabouts and other road enclosed sites in the town of Bracknell. Hemiptera were sampled using suction sampling and tree beating. A significant species–area relationship was found for arboreal Hemiptera, which was strongly related to habitat diversity. For both grassland plants and Hemiptera, grassland management, by mowing, had a significant effect on species richness. Despite the management grassland plants showed a significant species–area relationship. However the effect of management on Hemiptera was great enough to outweigh any area effect. As the size of open spaces is often constrained in urban areas, altering habitat management has a greater potential for enhancing biodiversity. For arboreal Hemiptera choice of trees for planting is of particular importance, while for grassland Hemiptera diversity would be increased with a reduction in the intensity of management, such a reduction in the frequency of mowing.

Modeling traffic flow at a single-lane urban roundabout

Abstract In this paper, we propose a new model to study traffic flow at a single-lane urban roundabout, using a multi-state cellular automata (CA) ring under the offside-priority rule (by which a vehicle entering gives way to one already on the roundabout). Each vehicle entering the roundabout is randomly characterized by a predetermined exit with specified probability. Driver behavior at the roundabout entrance is randomly grouped into four categories based on space required to enter the roundabout. Three aspects of roundabout performance in particular have been studied. The first looks at overall throughput (the number of vehicles that navigate the roundabout in a given time). This is considered for different geometries, turning and arrival rates (vehicles arrive at random with a Poisson distribution, with parameter λ ⩽0.5 in general for free flow). The second investigates changes in queue length, delay time and vehicle density (ratio of the number vehicles to the number of cells) for an individual road. The third considers the impact of driver choices on throughput and operation of the roundabout. We find that throughput is influenced by the topology of the roundabout and turning rates, but only incidentally by size. Throughput reaches a maximum for critical arrival rate on one or more roads. Driver behavior has considerable impact on overall performance, with rapid congestion resulting from reckless choices. Vehicles drive on the left in Ireland, but rules are generally applicable.

Emission and deposition of lead from motor exhausts — II. Airborne concentration, particle size and deposition of lead near motorways

Measurements were made of the particle size and concentrations of airborne lead beside a heavily travelled section of the M4 motorway, London, a steeply inclined section of the M40, and a busy urban roundabout in Chiswick, London. For both motorways, samples collected by impactors, centripeters and diffusion batteries confirmed electron microscope observations that most of the lead was associated with particles of < 0.1μm diameter. Beside the roundabout in Chiswick, 67% of the lead was >0.3 μm aerodynamic equivalent diameter compared with a figure of 33% for the motorways. Particle size was substantially unaffected by the incline on the M40, although significantly higher lead concentrations were observed beside the incline when normalised for traffic flow. Dry deposition of lead, measured by exposing trays of grass on the central reservation and at intervals from 0–100 m from the M4 motorway accounted for about 10% of the estimated emission of lead. Analysis of soils and standing vegetation within 100 m of the M4 accounted for 22% of the calculated total lead emitted since the motorway was opened. The significance of resuspension of lead from the road surface is discussed. The possible use of hedges and belts of trees for limiting dispersion of lead from motorways is critically assessed.