Roundabout Approach Research Articles

Impact of Splitter-Island on Pedestrian Safety at Roundabout Using Surrogate Safety Measures: A Comparative Study

This study aimed to investigate the effects of the splitter-island on pedestrian safety at roundabouts, considering the interaction between pedestrians and vehicles. Traffic accident statistics have traditionally been used to assess traffic safety. This method has severe limitations when used to investigate the impact of a particular feature of traffic facilities on safety at a microscopic level. Most previous research on surrogate safety measures (SSMs) had, on the other hand, focused on studying the safety of traffic operation conditions. The impact of a particular geometric feature of a roundabout on safety has so far received little attention in the literature. Therefore, we evaluated pedestrian safety in the presence and absence of physical splitter-islands by taking advantage of comparative statistical analysis (SA) and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) methods. The Towa-Cho roundabout in Nagano prefecture in Japan was chosen for this study because it allows for five approaches, three with a splitter-island and two without. From 33-hr video data, a total of 343 and 183 potential pedestrian-vehicle conflicts were detected in three crosswalks with splitter-islands and two crosswalks without splitter-islands, respectively. The minimum time-to-collision (TTCmin), post-encroach-time (PET), maximum speed (MaxS), and maximum deceleration-to-safety (DTS) measures were monitored using particle tracking velocimetry (PTV) software for potential pedestrian-vehicle conflicts. It was found that geometric differences were significantly reflected by SSMs, and TTCmin was the most efficient among all. It was concluded that the splitter-island had a better safety performance than the roundabout approach.

Safety Index for evaluation of urban roundabouts

Recently, there is a growing interest in road safety assessments based on the examination of the characteristics of the road aimed at identifying the presence of risk factors. This approach, named road assessment program or network wide road safety assessment, is required by the EU Directive 2019/1936 on road infrastructure safety management. Reliable procedures for assessing the inherent safety of all the elements of the road network are required to conduct roadway safety assessments. To provide a contribution toward the development of procedures for network wide road safety assessment, this paper develops and validates a Safety Index (SI) for evaluating urban roundabouts. The SI is assessed both at the roundabout level as well as at the roundabout approach level. This procedure detects the safety issues that are the largest contributors to crash risk in order to identify the safety measures that provide the greatest crash reduction at roundabouts. The SI is formulated by combining two components: the exposure of road users to road hazards (Exposure) and the risk factors which increase the probability of involvement in crashes (Risk Index). The procedure considers 33 detailed safety issues and 5 general safety issues to compute the Risk Index. Criteria for identifying and ranking the safety issues are defined.The SI procedure was validated in a sample of 50 urban roundabouts located in Rome, Italy. The sample consisted of 12 single-lane roundabouts and 38 two-lane roundabouts, with a total number of approaches equal to 179. In these roundabouts, the SI scores and the EB crash estimates were compared with reference both to the whole roundabouts as well as to the single roundabout approaches. The correlation between the SI scores and EB estimates was highly significant both at the roundabout level (R2 = 0.85, t = 16.49, p-value < 0.001) as well as at the approach level (R2 = 0.56, t = 14.88, p-value < 0.001). The results from Spearman's rank-correlation analysis provided further validation for the SI indicating that rankings from the SI and the EB estimates agree at the 99.9 % confidence level both at the roundabout level (ρs = 0.80) as well as at the approach level (ρs = 0.70).

Evaluation of Factors Influencing Roundabout Performance in Atlanta

This paper evaluates the potential impacts of various geometric and operational parameters on gap-acceptance behavior for approaches to roundabouts in the metropolitan area of Atlanta, Georgia. Twelve roundabouts were selected to provide a range of different conditions such as number of legs, number of circulating lanes, conflicting volumes, presence of pedestrian crossings, and so forth. Observational data were collected at these roundabouts using a remotely operated drone equipped with a stabilized high-resolution (4K) video camera operating at a sufficient altitude (just less than 400 ft/120 m) to encompass the complete facility within a single frame. The resulting videos were processed using commercial machine vision analysis supplemented by additional computer-assisted analysis to determine vehicle trajectories, spacings, and potential conflicts on a frame-by-frame (0.033 s) basis. These data, in turn, were used to establish gap-acceptance behavior of each roundabout approach and, through the use of logistic regression on the data, to establish observed critical headways (defined as the logistic inflection point [ t50]). The variability of observed headways was compared against known parameters of both the roundabout and of the specific approach to develop a descriptive/predictive model as to how critical headways and gap-acceptance behavior were affected by variations in these parameters. Several factors were observed to have significant impacts on critical headways, including geometric (size category of the roundabout, number of legs, and visual angle to the upstream approach), environmental (presence of a state route on the upstream approach, presence of additional conflicting lanes, presence of a pedestrian crosswalk on the approach), and operational (approach speeds) factors.

Η θεώρηση του Vygotsky για την τυπική και «παρεμποδισμένη» ανάπτυξη

Vygotsky has advocated that the dialectical relation between typical and impeded development carries a unique quality. His approach to development requires a holistic, qualitative education that addresses the entire personality. The theoretical approaches that were transferred into and adopted by pedagogy were the unities of the individualism and collectivism, and the zone of proximal development (ZPD). Vygotsky’s educational approach to childhood resulted from two alternating pathways of his thought: his broader interest in language and his personal experiences and achievements. In the context of his dialectical approach, he views the typical and atypical impeded child’s development as a joint unit and therefore atypical development is a unique quality dialectically associated with typical development. The term “defectology” he introduced describes the study of atypical impeded development of children with physical and mental deficiencies. A child’s handicap concurs with the two pathways of development that typical development follows: that of biological maturity and that of socialization process during which a child acquires knowledge and the capacity to use cultural tools, i.e. to use higher mental functioning through collective activities. Most often a handicapped child with deficits is unable to cope with the school structure or to participate in learning activities without adult support (ZPD). In this context, Vygotsky claims that the education of these children can be appropriated through a roundabout approach that aims to reconstruct the child’s personality in terms of dialectical relations and activities compatible to the child’s cultural environment; thus children with deficits are treated as productive members within the environment they belong to. In the context of contemporary inclusive education, Vygotsky’s ideas can contribute to the implementation of differentiating instruction, collaborative teaching and collective activities through the child’s daily social activities, practices that promote alternative ways of action and teaching that benefit all children.

Characteristics of vehicle speeds on roundabout approach

The choice of the type of intersection and their design elements has been done in dependence of the street category and its functions on the network, as well as the relationship between the forecast traffic flow and required capacity. Street network design elements have direct influence on traffic condition, among other things, also on the vehicular speed. In this paper, the analysis of the vehicular speed on the roundabout intersection approaches was conducted. The analysis was conducted in order to get a relevant parameter that could answer the questions how to this type of intersection impact on the speed of approaching vehicles. The survey was realized on the street network in residential zone in the city of Novi Sad.

A Novel Control Strategy for Roundabout System with Origin-Destination Flow Pattern

Abstract This study proposes and evaluates a novel control strategy that aims to regulate the roundabout approach inflow by taking into consideration its origin-destination demand pattern. The average density of the circular segment is controlled at a pre-defined range of optimal density which is derived using the Macroscopic Fundamental Diagram (MFD). A case study of a two-lane roundabout in Selangor, Malaysia, is developed in a microscopic simulation environment to study and test the effectiveness of the proposed control strategy. It is shown that the proposed control strategy could reduce the system travel time and increase throughput especially during medium to high level of demand. In addition, the sensitivity analysis reveals that its effectiveness is sensitive to the parameters’ setting such as: the roundabout lane geometry, origin-destination demand level, and traffic congestion level.

Impact of Including Exiting Vehicles in Single-Lane Roundabout Capacity Models

Roundabouts are classified as alternative intersection forms because they provide operational conditions not found at conventional intersections (e.g., a low-speed environment and fewer possible vehicle conflicts). Such conditions provide a combination of safety and operational benefit that normally is not achievable at a conventional intersection. The ability to predict capacity accurately is important when alternative intersection designs are examined. Highway Capacity Manual 2010 provides a current method for determining the capacity of a roundabout approach in which vehicles that exit on the same approach are considered not to influence capacity. However, the inclusion of exiting vehicles in the model creates a different circulating vehicle gap distribution (dividing larger gaps into smaller gaps) that reduces the number of opportunities to measure follow-up headway. Also, most critical headway values for the analysis are smaller than the critical headway values found when exiting vehicles are excluded. Capacity equations were developed from video imagery recorded for 28 approaches at 13 roundabouts, and the impact of including exiting vehicles in the analysis of single-lane roundabout capacity was evaluated. Vehicles exiting the roundabout were found to have a measurable impact on the estimated capacity of the roundabout approach. Both follow-up and critical headway values decreased when exiting vehicles were included. Also, the estimated capacity including exiting vehicles was found to increase or decrease (relative to capacity estimates that excluded exiting vehicles) depending on the percentage of conflicting vehicles that were exiting vehicles.

A roundabout approach to control morphological orientation and solar-cell performance by modulating side-chain branching position in benzodithiophene-based polymers.

To be meaningful to guide the rational design of novel high-performance conjugated semiconductors, we prepared three benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymers by systematically moving the branching point of the alkyl chain. The effect of side-chain engineering was thoroughly investigated by a range of techniques. We demonstrate that a subtle change in the branching position in the BDT core can have a critical impact on polymer packing and preferential backbone orientation in thin films; copolymers made from BDT and thieno[3,4-c]pyrrole-4,6-dione units (TPD) adopt more of a face-on orientation as the branching point is shifted closer to the backbone, which can be correlated with a dramatic difference in solar-cells performance. The high short-circuit current density (11.6 mA cm(-2) ) for the copolymer with one carbon atom between the alkoxylated oxygen atom and the branching point results from its predominantly face-on orientation and smoother surface in thin films, which results in power conversion efficiencies as high as 4.56 %.

Effects of Approach Speed at Rural High-Speed Intersections

Speed can increase the risk of injury-producing crashes, especially at intersections where vehicles may be approaching and entering the intersection with high speed differentials. It is known that roundabouts force all drivers to reduce their speed in the intersection; however, speed data in advance of the roundabout approach were not available for roundabouts with high-speed approaches to verify this phenomenon. In this research, a comparative evaluation of the difference in the average approach speeds between rural roundabouts and rural two-way-stop-controlled intersections and between rural roundabouts with and without rumble strips on the intersection approaches was performed. Approach speed data proved that drivers could slow down in advance of roundabouts on rural roadways. The mean speed 100 ft from the yield line of the roundabouts was 2.5 mph lower than the mean speed 100 ft from the stop bar at stop-controlled approaches. Additionally, a comparison of roundabout approaches with and without rumble strips showed mean speeds 4.3 and 3.3 mph lower 100 and 250 ft from the yield line, respectively, for approaches with rumble strips; however, the variation in speeds increased with the introduction of rumble strips.

Effects of Crosswalk Location and Pedestrian Volume on Entry Capacity of Roundabouts

At roundabout approaches, vehicles must yield to pedestrians who are using crosswalks. The presence of pedestrians using the crosswalk at a roundabout approach thus decreases the entry capacity of the approach. This research used a calibrated microscopic traffic simulation model to study the effect of crosswalk location and pedestrian volume on the capacity of a two-lane approach entering a two-lane roundabout. The simulation results show that (i) at the same pedestrian volume, the crosswalk located further upstream from the yield line causes a smaller magnitude of reduction in the entry capacity, but there is no significant change in the entry capacity when the crosswalk is beyond three car-length upstream from the yield line; (ii) for the same crosswalk location and conflicting volume, the entry capacity reduces with increasing pedestrian volume, but the marginal reduction diminishes with increasing pedestrian volume. Linear regression equations for entry capacity adjustment factor for pedestrians as a function of conflicting volume have been developed. The adjustment factors are found to be lower than the values provided by the Highway Capacity Manual 2010 which are based on research conducted in Germany.

Event-Based Modeling of Driver Yielding Behavior to Pedestrians at Two-Lane Roundabout Approaches

Unlike other types of controlled intersections, drivers do not always comply with the "yield to pedestrian" sign at the roundabouts. This paper aims to identify the contributing factors affecting the likelihood of driver yielding to pedestrians at two-lane roundabouts. It further models the likelihood of driver yielding based on these factors using logistic regression. The models have been applied to 1150 controlled pedestrian crossings at entry and exit legs of two-lane approaches of six roundabouts across the country. The logistic regression models developed support prior research that the likelihood of driver yielding at the entry leg of roundabouts is higher than at the exit. Drivers tend to yield to pedestrians carrying a white cane more often than to sighted pedestrians. Drivers traveling in the far lane, relative to pedestrian location, have a lower probability of yielding to a pedestrian. As the speed increases the probability of driver yielding decreases. At the exit leg of the roundabout, drivers turning right from the adjacent lane have a lower propensity of yielding than drivers coming from other directions. The findings of this paper further suggest that although there has been much debate on pedestrian right-of-way laws and distinction between pedestrian waiting positions (in the street versus at the curb), this factor does not have a significant impact on driver yielding rate. The logistic regression models also quantify the effect of each of these factors on propensity of driver yielding. The models include variables which are specific to each study location and explain the impact size of each study location on probability of yielding. The models generated in this research will be useful to transportation professionals and researchers interested in understanding the factors that impact driver yielding at modern roundabouts. The results of the research can be used to isolate factors that may increase yielding (such as lower roundabout approach speeds), and can feasibly be incorporated into microsimulation algorithms to model driver yielding at roundabouts.

Delay Analysis of Single-Lane Roundabout with a Slip Lane under Varying Exit Types, Experimental Balanced Traffic Volumes, and Pedestrians, Using Microsimulation

A slip lane facilitates right-turning traffic flow, reduces approach delay, and reduces conflict points within a roundabout. In this paper the delay performance of a single-lane roundabout with an adjacent slip lane is modeled with the VISSIM microsimulation tool for three slip lane exit types (free-flow, yield, and stop) and the results are compared with a roundabout having no slip lane. The VISSIM assessment considers four experimental traffic percentage turning volume distributions as balanced flow scenarios (total traffic flow into and out of every roundabout approach is the same). Simulated slip lane right-turning traffic volumes range from 50 to 500 vehicles/h, and the four pedestrian volume levels range from 0 to 100 pedestrians/h. VISSIM results confirm that average delays in a roundabout with a slip lane are a function of circulating conflict volumes and are related exponentially to slip lane volumes regardless of the slip lane exit type. Results also indicate that a free-flow slip lane exit type best reduces total average delay in the roundabout and in the slip lane itself. Yield and stop slip lane exit types also reduce the roundabout total average delay but to a lesser degree. Finally, at a higher traffic volume, a free-flow slip lane exit type can increase roundabout delay from 6.6 to 34.7 s/vehicle if drivers must yield the right-of-way to high pedestrian traffic (100 pedestrians/h) crossing a free-flow slip lane (priority rule).

Operations of Modern Roundabout with Unbalanced Approach Volumes

This research examined the operations of a four-legged, two-lane modern roundabout with different combinations of approach volumes. Because of the insufficient number of roundabouts to collect field data, experiments were performed with the VISSIM microscopic traffic simulation model. The model's parameters were calibrated with real data collected at a four-legged, two-lane modern roundabout. Different combinations of approach volumes, which ranged from 400 to 1,600 vehicles per hour, were simulated to create relatively high or low traffic demand in one or two approaches. The performance of each roundabout approach was measured by average control delay and level of service. The results of the experiments highlight the potential operational issues of four-legged, two-lane modern roundabouts. The results are presented in three charts that may serve as a quick reference guide for engineers to determine whether a roundabout is a feasible type of intersection control for a given set of design volumes before in-depth engineering analysis is performed.

Conflict Models for Single-Lane Roundabout Slip Lanes from Microsimulation

Conflict patterns at single-lane roundabouts with and without slip lanes were evaluated and compared through VISSIM, the microscopic simulation program for multimodal traffic flow modeling, and surrogate safety assessment model (SSAM) analysis. From a sensitivity analysis of several volume distribution scenarios of the percentage of turning traffic, five zone-based conflict prediction models were developed through the use of Poisson regression. The models captured simulated conflict differences that resulted from the addition of a right-turn slip lane. The models were evaluated under three exit control scenarios (yield, stop, and free-flow merge). With SSAM analysis, the models predicted the occurrence of conflicts for roundabout zones with different R-squared values, which ranged from .69 to .97. The models were compared with national and inter-national crash prediction models for single-lane roundabouts and were further validated by actual crash data from 10 single-lane roundabouts in the city of Carmel, Indiana. The number of conflicts for a single-lane roundabout was predicted as a function of approach entry, circulation, and slip lane traffic flows and was determined to be sensitive to the slip lane exit type. Results confirmed that conflicts in the merge area were more frequent than in the roundabout approach area and that the installation of a free-flow slip lane exit type reduced overall conflict occurrence. The results demonstrated the usefulness of SSAM analysis for evaluating roundabout safety and developing an empirical relationship between simulated conflicts and field-observed crashes.

Effect of roundabout operations on pollutant emissions

This research quantifies the traffic and emission impacts of single lane roundabouts in urban corridors, based on experimental measurements of traffic and using the “Vehicle Specific Power” emission estimation methodology. Experimental data were gathered from single lane roundabouts located in Lisbon (Portugal) and Raleigh (US). Using congestion-specific vehicle speed profiles on the roundabout approaches, the emissions calculation methodology is able to quantify the relationships between vehicle dynamics and emissions. The main contributions are: the characterization of a limited set of synthetic speed profiles that occur at a roundabout approach, the frequency distribution of these profiles based on congestion levels, and the correlation between queue length and the number of stop and go cycles. Two different types of stop and go driving cycles for vehicles joining the queue at a roundabout were identified: short and long.

Comments on Roger Garrison's “A Roundabout Approach to Macroeconomics: Some Autobiographical Reflections”

Comments on Roger Garrison's “A Roundabout Approach to Macroeconomics: Some Autobiographical Reflections”

Including Exiting Vehicles in Capacity Estimation at Single-Lane U.S. Roundabouts

The current model used in the United States to predict approach capacity at a single-lane roundabout uses information about entry driver behavior in response to the circulating traffic stream only. There is no procedure for including exiting vehicles in capacity estimation. Exiting vehicles are vehicles that leave the circulating stream of traffic by maneuvering into the exit lane at a roundabout approach. Exiting vehicles are known to have an effect on capacity at roundabout approaches in other countries, but their effect in the United States is not known. The purpose of this research is to determine whether including exiting vehicles improves capacity estimation at a roundabout approach. An exploration of the relationships of the proportion of exiting vehicles and the width of the splitter island to approach capacities is included. Capacities were estimated both with and without exiting vehicles as part of the conflicting flow and compared with measured field capacities. The findings demonstrate that capacity estimates with exiting vehicles result in improved prediction of the actual capacity of a roundabout approach over estimates without exiting vehicles. The proportion of exiting vehicles in the major stream and the width of the splitter island appear to provide some benefit in capacity prediction, but exactly how these parameters can be incorporated into the capacity prediction process must be further explored.

Including Exiting Vehicles in Capacity Estimation at Single-Lane U.S. Roundabouts

The current model used in the United States to predict approach capacity at a single-lane roundabout uses information about entry driver behavior in response to the circulating traffic stream only. There is no procedure for including exiting vehicles in capacity estimation. Exiting vehicles are vehicles that leave the circulating stream of traffic by maneuvering into the exit lane at a roundabout approach. Exiting vehicles are known to have an effect on capacity at roundabout approaches in other countries, but their effect in the United States is not known. The purpose of this research is to determine whether including exiting vehicles improves capacity estimation at a roundabout approach. An exploration of the relationships of the proportion of exiting vehicles and the width of the splitter island to approach capacities is included. Capacities were estimated both with and without exiting vehicles as part of the conflicting flow and compared with measured field capacities. The findings demonstrate that capacity estimates with exiting vehicles result in improved prediction of the actual capacity of a roundabout approach over estimates without exiting vehicles. The proportion of exiting vehicles in the major stream and the width of the splitter island appear to provide some benefit in capacity prediction, but exactly how these parameters can be incorporated into the capacity prediction process must be further explored.

A Roundabout Approach to Macroeconomics: Some Autobiographical Reflections

Roundaboutness is a concept featured in Aus trian capital theory. Homely stories about the bare handed catching of fish are a prelude to a discussion of the economy's capital structure. The outputs of some stages of production become inputs to others. Production takes time. The capital structure, broad ly conceived, has a temporal profile?one that can be modified in response to changes in intertemporal consumption preferences and resource constraints. This was the central message of Eugen von Bohm Bawerk (1959). Alfred Marshall, who theorized in terms of the short period and the long period, taught us that most problems in economics stem from the ever-critical time element. I think Marshall was right on time. But I also believe that a healthy understanding of some of those problems?particularly the ones in macroeconomics?is not best facilitated by his sim ple short-period/long-period distinction. Adopting Marshallian methods, John Maynard Keynes dealt with the polar extremes in the quality of expectations, casting serious doubt about the via bility of a market system. In the short run, the time element itself is problem: Short-run expectations faithfully reflect reality. If the level of spending changes, the multiplier process plays itself out in a clockwork sequence of spending and earning, even tually achieving a new circular-flow equilibrium. Long-run expectations, however, are another mat ter. Here, the time element is a problem: These expectations, if you can call them that, are baseless. The future is shrouded in an impenetrable fog of uncertainty, leaving the current level of investment spending to be determined by unruly psychological factors?Keynes's infamous animal spirits. The resultant circular flow will gush and ebb and even on average may not entail enough flow to fully employ the labor force. The circular-flow framework, exercised in both its short-run and long-run modes, seems to me to be exactly the wrong framework for understanding and dealing with the time element in macroeconomics. Identifying the polar cases of no and debilitating doesn't get us any closer to a solution to all those intermediate cases lying between the poles. The tell-tale feature that inevitably characterizes this framework has been recognized in recent years by Robert Solow (1997)?namely the lack of any real coupling (Solow's term) between the short and the long run. In Solow's reckoning, the two runs simply divide our discipline's subject matter into (1) the problem of maintaining full employment of existing resources and (2) the determinants of economic growth. A viable alternative to the Keynesian circular flow framework is the Austrian means-ends frame work. People employ means (investment) to achieve ends (consumption). In a capital-using economy, there is a significant time dimension sep arating means and ends. We realize that some pro duction processes take more time than others. And, thinking in macroeconomic terms, we recognize that production time can increase or decrease for the economy as a whole as market conditions war rant. In the medium run (a term from Solow, 2000), the problem is one of adjusting production decisions to (intertemporal) consumption prefer ences?a problem that Axel Leijonhufvud (1998) urges us to put back on our macroeconomic agenda. The only solution available in a decentralized econ omy is one involving entrepreneurial responses to changing market signals and especially to changes in the rate of interest. The time element here (Bohm-Bawerk's roundaboutness of production

Progress in Coupling Systems Boosts LC/MS Prospects

Liquid chromatography /mass spectrometry (LC/MS) soon will become a formidable competitor to gas chromatography/ mass spectrometry (GC/MS), according to evidence presented at the recent American Chemical Society national meeting in Washington, D.C. The combination of GC and MS has led to the development of powerful tools for identifying and quantitating trace components of complex mixtures. Its usefulness is not universal, however. One problem has been that many compounds, because of their involatility or their heat sensitivity, just aren't amenable to GC, at least not without the application of derivatization techniques or some other roundabout approach. The obvious solution to that difficulty— coupling liquid chromatography and mass spectrometry—has turned out to be harder than the analogous GC/MS case. Nevertheless, progress is being made on a number of fronts. At a Division of Analytical Chemistry symposium on LC/MS, Bruce A. Thomson, a senior research scientist with Toronto-based Sciex, conceded that...