2013 Session: 542

• Delay Analysis of Simulated Single-Lane Roundabout with Dedicated Bus/Truck Slip Lane
  Abstract: Simulated delay performance of single-lane roundabouts with an adjacent slip lane (bypass) for right turns is evaluated under varying bus and truck traffic percentages and two slip lane exit types (free-flow and yield). A microsimulation assessment considers experimental balanced flow scenarios with different right-turning bus and truck traffic percentages (low, moderate, and high) and with a proposed dedicated lane, compared to no slip lane. Simulated slip lane right-turning traffic volumes range from 50 to 500 vehicles per hour. Results indicate that average delay of a roundabout with slip lane and under varying bus or truck traffic has confirmed a non-linear relationship with slip lane volumes and is sensitive to changing bus or truck traffic percentages, before oversaturation occurs. As expected, results indicate that a free-flow slip lane exit type significantly reduces total roundabout average delay, compared to having no slip lane with bus or truck traffic. Yield slip lane exit types also reduce roundabout total average delay with bus or truck traffic but to a lesser degree. With a free-flow slip lane exit type designated as a dedicated bus lane, overall average roundabout delay was reduced 12% (the estimated 95% confidence interval of reduction estimated between -19% and -5%). With a dedicated truck slip lane, overall average roundabout delay was reduced 9% (the estimated 95% confidence interval of reduction estimated between -16% and -2%). A dedicated bus slip lane shows a more significant improvement of delay than a dedicated truck slip lane, for a single-lane roundabout.Key words: Roundabout, slip lane, average delay, dedicated bus or truck lane, VISSIM.
  Authors: Al-Ghandour, Majed N.
  Authors: Al-Ghandour, Majed N.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-0151
• Roundabout Networks for Robust, Walkable Communities
  Abstract: Modern roundabouts have continued to proliferate in the United States since the first were constructed in the 1990s. Roundabouts offer well-documented safety, capacity, and environmental benefits as compared with most other intersection types. Yet most U.S. roundabouts are built at either isolated locations or in short corridors. The Complete Streets movement has made great inroads in getting engineers to consider the needs of all users when designing a roadway. Yet jurisdictions which have adopted Complete Streets have largely confined themselves to cross sections; the actual layout of the street network is relatively unchanged. New Urbanism has encouraged planners and developers to rethink the layout and spatial arrangement of local streets, but these concepts have typically not made it to the adjacent arterial network.This paper proposes a roundabout-based network of through streets which integrates Complete Streets and Access Management concepts with provision for mass transit and non-motorized transport. A variety of intersection and corridor treatments are explored for interfaces between the roundabout network, local streets, limited access facilities, and existing arterial grids. The roundabout network is intended as a drop-in replacement for the major thoroughfare plans common to most fast-growing cities.
  Authors: VanElswyk, Abram
  Authors: VanElswyk, Abram
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1042
• Study on Optimization Method of Signal Control at Four-Leg Roundabout Based on Single Release
  Abstract: This paper proposes a single release based signal control method for four-leg roundabouts. Single release is a signal control method of roundabouts, which makes each approach as a single phase, and releases the vehicles of each approach clockwise. In order to improve the capacity, two kinds of optimizing control schemes are presented. Based on the schemes, the phase design was made and the Webster¡¯s optimal cycle length formulation was improved. By comparing the two optimizing signal control schemes, the applicable condition of the signal control schemes is discussed. Finally, a simulation study was conducted for a real Roundabout, and the result shows the validity of optimization control schemes.
  Authors: Zuo, Junzhong; Xu, Liangjie; Cheng, Yang
  Authors: Zuo, Junzhong; Xu, Liangjie; Cheng, Yang
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1156
• Calibration of VISSIM Roundabout Model: A Critical Gap and Follow-up Headway Approach
  Abstract: VISSIM roundabout models have been widely applied in practice to facilitate analyzing the operational performance of roundabouts. To prepare a VISSIM roundabout model for analysis, an essential prerequisite is to calibrate the model by adjusting parameters until real-world roundabout operations are reproduced in the simulation model. Previous calibration research has used qualitative analysis to study the impact of VISSIM parameters on roundabout capacity. Comprehensive calibration guidelines, parameter values based on field data, and quantitative sensitivity analyses of parameters are necessary to facilitate accurate modeling of roundabouts. This paper addresses these important needs. Speed trajectories of free-flow entering vehicles were collected in the field using a radar sensor. Analysis identified that the approach to a roundabout entrance can be divided into four speed zones reflecting different stages of drivers’ deceleration maneuver. Location, length, speed distribution, and deceleration rate parameters for the VISSIM Reduced Speed Areas (RSA) were determined through the analysis of the radar data. Comparisons between Conflict Areas (CA) and Priority Rules (PR) were also investigated, and revealed that using PR can result in more consistent and repeatable gap acceptance behavior. In addition, the impact of VISSIM parameters on critical gap and follow-up headway was quantitatively analyzed through sensitivity analysis of minimum gap for PR, speed distribution and deceleration rate for RSA, and additive and multiplicative settings for the Wiedemann 74 model. Numerical recommendations for calibrating VISSIM roundabout models were ultimately developed, and validated via a case study.
  Authors: Li, Zhixia; DeAmico, Michael; Chitturi, Madhav V.; Bill, Andrea R.; Noyce, David A.
  Authors: Li, Zhixia; DeAmico, Michael; Chitturi, Madhav V.; Bill, Andrea R.; Noyce, David A.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1176
• Evaluation of Effect of Pedestrian Crossings on Roundabout Performance Using Microsimulation
  Abstract: Most specialized manuals recommend the placement of pedestrian crossings at 10/15 meters from the roundabout carriageway, in order to minimize the pedestrian disruption on the global functioning of the intersection. Normally, this recommendation is based on empirical relationships without any scientific based studies that prove its efficiency and adequacy. In this context, this paper is focused on the analysis of the influence that the presence of different locations of pedestrian crossings has in the roundabout performance level, using microssimulation techniques. The roundabout performance level is evaluated according to two indicators: vehicle traffic flows and average travel times. The results proved interesting showing that the effect of pedestrian crossing only takes a significant influence in terms of average travel time and for high traffic and pedestrian demand levels. In spite of this it appears that the effect is more pronounced in exit section compared to the entry. For saturation levels below 70% the effect of the presence of pedestrian crossing was practically negligible, regardless of the section on analysis. It is concluded that the usual practice of locating the exit crosswalks at approximately 15 meters from the exit section seems to be an equilibrated solution, regarding the smoothness of traffic and the walking distance. However for traffic calming applications the location of pedestrian crossings near the circulatory ring delimitation seems perfectly acceptable.
  Authors: Bastos Silva, Ana; Cunha, Joana; Relvão, Tiago
  Authors: Bastos Silva, Ana; Cunha, Joana; Relvão, Tiago
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1467
• Prediction of Capacity for Roundabouts Based on Percentages of Trucks in Entry and Circulating Flows
  Abstract: The objective of this study is to develop the method of adjusting gap acceptance parameters for trucks to estimate capacity at roundabouts. Since driver¡¯s gap acceptance behavior is not only affected by trucks in the entry flow, but also trucks in the circulating flow, critical headways were separately estimated for various combinations of vehicle types in the circulating flow at 11 roundabouts in Ontario, Vermont and Wisconsin. Since truck percentage is different in different entry leg, the critical headways and follow-up times were estimated at each leg separately. The variation in gap acceptance behavior was also observed at one of the eleven roundabouts for 13 consecutive days to evaluate statistical significance of difference in the behavior between two entry legs. The results show that the new adjusted critical headway improved the accuracy of capacity estimation, and the critical headways were significantly different between the two legs with different truck percentages in the entry flow. The study provides an insight into how to capture the effect of trucks on roundabout capacity.
  Authors: Lee, Chris; Khan, Moayed Naeem
  Authors: Lee, Chris; Khan, Moayed Naeem
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1391
• Analysis of Sight Distance, Crash Rate, and Operating Speed Relationships for Single-Lane Roundabouts in the United States
  Abstract: This paper seeks to determine whether a relationship exists between sight distance parameters, crash rates and operating speeds at low volume single lane roundabouts in the United States (US). Establishing an understanding of the interaction of design, operations, and crash performance would be a step forward in the development and application of performance-based standards for roundabouts. As part of the specific objective of this paper, research was done to quantify the relationship between crash rates, sight distance parameters and operating speeds based on crash, traffic and geometric data from 72 approaches to 19 single lane roundabouts in six states. The data for these sites were broken into two groups based on the posted speed limit. The research findings provided insight into the operational and safety effects of sight distance geometry at roundabouts. This research also identified a methodology that provides guidance as to the development of performance-based standards which rely on a better understanding of those relationships. In general, these findings were consistent with previously conducted studies and indicated that exceeding sight distance thresholds increases the risk of crash occurring. It was also found that exceeding sight distance thresholds yielded greater speed differentials between the approach and the entry to these roundabouts. This research methodology and corresponding results can advance the state of practice closer towards understanding the relationships of sight distance design attributes-operational characteristics and safety metrics for low volume single lane roundabouts which is necessary to in the creation of performance-based standards.
  Authors: Zirkel, Brian; Park, Seri; McFadden, John; Angelastro, Michael; McCarthy, Leslie Ann
  Authors: Zirkel, Brian; Park, Seri; McFadden, John; Angelastro, Michael; McCarthy, Leslie Ann
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1847
• Estimating Turning Movements at Roundabouts Using Bluetooth Technology
  Abstract: Turning movement counts at Roundabouts have historically been difficult to acquire. With the advent of Bluetooth wireless communication devices becoming commonplace for individuals to own and possesses while operating a vehicle, an opportunity was created to investigate the feasibility of applying this technology to turning movement counts at roundabouts. Two different locations were studied in Kansas, a rural five-leg, and an urban four leg roundabout were chosen. Bluetooth data loggers were deployed upstream of the central island at each location from which origin-to-destination leg data could be captured. When turning movement percentage data was compared to ground truthed human observations and statistically compared, the rural location was not statistically different, and the urban location barely was statistically different.
  Authors: Rescot, Robert Andrew; Schrock, Steven D.
  Authors: Rescot, Robert Andrew; Schrock, Steven D.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-2265
• Roundabout Critical Headway Measurement Based on High-Resolution Event-Based Data from Wireless Magnetometers
  Abstract: Critical headway is an important parameter for roundabout design, particularly in regards to analytical modeling approaches. These models have been developed over the past 30 years and were typically developed using data obtained from manually reduced video and/or field observations. This paper reports on the application of wireless magnetometers to collect point presence detection to calculate the rejected critical headways. Data was collected at a single lane roundabout in Carmel, IN. Carmel, IN is a community with over 60 roundabouts in operation for several years, representing a community highly experienced in using roundabouts. Over 260,000 entering vehicles were observed at one of the single lane roundabouts over a two week period with over 45,000 rejected headways analyzed. For the roundabout studied, 75% of the rejected headways were found to be less than 3.0 seconds. The rejected headways values were somewhat less than reported in NCHRP Report 572, perhaps due to the evolving driver familiarity with using roundabouts in a community with a particularly large number of roundabouts. The rejected headway characteristics observed suggest that as roundabouts become more common throughout the U.S., it may be appropriate to revisit some of the basic traffic engineering parameters used for analysis, much like the traffic signal community did with saturation flow rate in the 1990s. The techniques presented in this paper could be scaled to several roundabouts with varying geometrics and traffic to diversify the data set necessary to update some of the values developed in the last decade before roundabouts were common in the U.S.
  Authors: Hainen, Alexander Michael; Rivera, Erick Manuel; Day, Christopher M.; McBride, Michael Thomas; Grimmer, Gannon; Bullock, Darcy M.
  Authors: Hainen, Alexander Michael; Rivera, Erick Manuel; Day, Christopher M.; McBride, Michael Thomas; Grimmer, Gannon; Bullock, Darcy M.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-3316
• Hazardous Bicycle Maneuvers at Single-Lane Roundabouts in Massachusetts: A Conflict and Events Study
  Abstract: Roundabouts have been known to relieve congestion, reduce travel times, and decrease accident rates. Studies indicate that despite reducing the total crash rate, roundabouts show a significant increase in the proportion of crashes that involve a cyclist. These crashes are primarily due to cyclists who create a bicycle lane through the roundabout. The purpose of this study is to determine if cyclist safety should be of particular concern in roundabouts in Massachusetts, specifically whether or not cyclists and/or vehicles are performing maneuvers outlined in previous studies to be major contributors for cyclist-based crashes. A custom conflict/event and compliance study was designed. Preliminary studies were performed at a roundabout located at the University of Massachusetts, Amherst. Subsequent studies were performed at various roundabout locations throughout Massachusetts. This study recorded all bicycle movements and any observed bicycle/vehicle interactions, tracking specific maneuvers that could create a hazardous or unsafe situation. The number of bicycles that performed unsafe maneuvers was compared to the total number of bicycles observed traversing the roundabout.This study confirms that some cyclists who use the roundabout at the University of Massachusetts Amherst operate in an unsafe manner or in a way defined to be a leading cause of accidents involving a bicycle in a roundabout (32% of all observed cyclists). Similar results were found at other roundabouts throughout Massachusetts (33% of all observed cyclists). Possible solutions were postulated.
  Authors: Berthaume, Andrew Leo; Knodler, Michael A.
  Authors: Berthaume, Andrew Leo; Knodler, Michael A.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4216
• Experimental Analysis and Methodological Approach by Microsimulation of Crossing-Speed Distribution on Small- and Large-Diameter Roundabouts
  Abstract: In literature many studies have shown how speed distribution in roundabouts, together with other parameters (entering flow, circulating flow, entry curvature, entry path radius, entry width, approach width, ratio of inscribed circle diameter/central island diameter, angle to next leg, etc.), can be used as a measure of safety performance for these kind of intersections. The wide use of several micro-simulation models for a preventive analysis of roundabouts performance (capacity, delays, safety, etc.) emphasizes the need for a deeper study of the most sensitive parameters for a better fitting between simulated and observed traffic conditions.This paper focuses on an experimental analysis of the through movement in two roundabouts characterized by different values of the inscribed circle diameter (D1˜1/2•D2) and located close together in the same road-straight in the University Campus of Arcavacata, Italy. The main aim of the research is the suggestion of a methodological approach to the simulation process of the through movement by the use of VISSIM® micro-simulation software for the above mentioned roundabouts.Results concern the following issues: (i) coherence validation of experimental data regarding speed distributions along the trough movement as a function of roundabout radius; (ii) methodological and procedural issues related to the implementation of simulation parameters in VISSIM, particularly referring to speed distributions along the crossing movement, in order to better understand the effects of the change of roundabouts geometric features on simulation results.
  Authors: Vaiana, Rosolino; Gallelli, Vincenzo; Iuele, Teresa
  Authors: Vaiana, Rosolino; Gallelli, Vincenzo; Iuele, Teresa
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-3787
• Crash Severity Analysis at Roundabouts: Case Study in Quebec, Canada
  Abstract: Numerous studies both in North America and abroad have studied the roundabout as a means to improve the capacity and safety of intersections. The focus of these studies has been to reduce both the number and the severity of accidents, and have generally come to agreeable results. Nevertheless, few studies have dealt with the identification of accident factors within roundabouts. The varied physical and environmental characteristics of Quebec’s roundabouts and the behavioral traits of its drivers requires further study in order to help reduce the occurrence and severity of accidents. This paper presents a crash severity analysis to identify the effects of different contributing factors on injury severity outcomes. To achieve this, an ordered logit modeling technique was used for the analysis. Moreover, an important effort was made to integrate an accident database containing accident records from the year 2000 to 2011. Among other results, it was found that factors such as a larger number of involved vehicles, accidents occurring within the intersection, vehicle rollovers, the involvement of buses, accidents occurring in the dark on unlit roads and snow conditions led to increased injury severity within roundabouts, whereas factors associated to accidents involving only cars, animal strikes and snow-covered roadways were found to reduce the likelihood of severe injuries.
  Authors: Burns, Shaun; Miranda-Moreno, Luis Fernando; Saunier, Nicolas; Ismail, Karim
  Authors: Burns, Shaun; Miranda-Moreno, Luis Fernando; Saunier, Nicolas; Ismail, Karim
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4527
• Using Vehicle Simulations to Understand Needs and Strategies for Accommodating Oversize, Overweight Vehicles at Roundabouts
  Abstract: 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 vehicles, sometimes called “Superloads”. To use these OSOW vehicles as a design vehicle for roundabouts could negate the benefits of roundabouts which rely on being designed to operate at slower speeds from adequate deflection. 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 Federal Highway Administration (FHWA) latest roundabout guide (NCHRP 672). Six OSOW check vehicles from the Wisconsin Department of Transportation’s (WisDOT) 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 and their space requirements were analyzed in detail. Various strategies for better accommodating these OSOW check vehicles were suggested and experimented with in this study. 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. The needed total truck apron was calculated for the accommodation strategies. Tables were presented to show the total truck apron area required for various accommodation strategies.
  Authors: Godavarthy, Ranjit Prasad; Russell, Sr., Eugene R.; Landman, Dean
  Authors: Godavarthy, Ranjit Prasad; Russell, Sr., Eugene R.; Landman, Dean
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4725
• Study of Accommodating Oversize, Overweight Vehicles at Roundabouts
  Abstract: Roundabouts can offer several advantages over signalized and stop-controlled intersection alternatives, including better overall safety performance, lower delays, shorter queues, better management of speed, and opportunities for community enhancement features. In some cases, roundabouts can avoid or delay the need for expensive widening of an intersection approach that would be necessary for signalization.However, potential use of roundabouts with all their benefits may be greatly diminished if they cannot accommodate oversize/overweight vehicles (OSOW). How to accommodate OSOW at roundabouts is the central issue and the need for this research.This research project is necessary to compile current practice and research by various states and countries related to the effects OSOW have on roundabout location, design, and accommodation. Second, the research will attempt to fill in information gaps with respect to roundabout design and operations for these classes of vehicles. Currently there is little information available for accommodating the OSOW vehicle classes in roundabout design.To obtain additional information and data needed to complete the stud, the following were performed:•Surveys of all the states and a sample of the trucking industry•Personal contact with designers and researchers and examples provided•Simulations of OSOW operations at roundabouts. Based on material gathered for this study, surveys and interviews, it may be possible to accommodate OSOW at roundabouts with designs that consider the following: widened entries and exits, unobstructed central islands with large truck aprons, outer truck aprons, bypass lanes and lanes through the center island, mountable curbs, no vertical obstructions on the splitter islands, easily mountable curbs 3 inches or less, and with signs, light poles etc. outside of the turning paths and/or designed to be easily removed.
  Authors: Russell, Sr., Eugene R.; Landman, Dean; Godavarthy, Ranjit Prasad
  Authors: Russell, Sr., Eugene R.; Landman, Dean; Godavarthy, Ranjit Prasad
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4759
• Roundabout Versus Traffic Signal Control: Comparative Analysis
  Abstract: The research presented in this paper quantifies the efficiency, energy, and environmental impacts of single-lane and two-lane roundabouts compared to all-way stop control (AWSC), two-way stop control (TWSC), and traffic signal control. Furthermore, the research develops guidelines for the identification of the optimum intersection control as a function of the level of intersection demand, the distribution of demand across various approaches, and the distribution of approach demand between left, through and right turner movements. The research first compares the alternative control strategies using field data collected from two roundabouts in the Blacksburg Area. The field data are then used to validate the INTEGRATION software for the modeling of different intersection control strategies. The field data demonstrate that in both cases roundabouts are the optimum control strategy. The sensitivity analysis demonstrates that single-lane roundabouts are more effective for high through and right turn demand levels and less effective for high left turn demands in comparison to other isolated intersection control strategies. The two-lane roundabout results suggest roundabouts are effective regardless of the demand level and distribution of demand across the various movements.
  Authors: Wang, Zhao; Boon, Teck Ong; Rakha, Hesham
  Authors: Wang, Zhao; Boon, Teck Ong; Rakha, Hesham
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4422
• Synthesis of Roundabout Geometric Capacity Measurement: Calibration and Validation to U.S. Field Measurements
  Abstract: The implementation of modern roundabouts in the U.S. began in the 1990s. Since then U.S. researchers and practitioners have increasingly debated which capacity estimation method(s) are most suited to U.S. conditions. Capacity research continues in the US, as it has for the past 50 years in some other countries.Early U.S. research concluded that international models over predict U.S. roundabout capacities. This has raised questions about the transferability of non US models to US conditions. Such questions include: are non US drivers more experienced with roundabouts: is their driver behavior different to US drivers? Does the different size of cars and trucks have an effect? Will such differences persist into the future?Recent independent capacity research on saturated roundabouts is providing increasing support for the transferability of the U.K. empirical capacity model to US conditions. This model derives capacity from detailed geometry, with six geometric parameters per leg. The wide range of all the geometric parameter encompasses entire spectrum of modern Roundabout design. This paper provides a synthesis of the development of the UK empirical model and reviews recent US research and data collection, comparing HCM 2010 calibration and validation and the transferability of the UK geometric capacity model to the US.
  Authors: Johnson, Mark T.
  Authors: Johnson, Mark T.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4790
• Traffic Capacity Models for Mini-Roundabouts in the United States: Calibration of Driver Performance in Simulation
  Abstract: The design of mini-roundabouts has been around and practiced in Europe for decades. It has been a successful and low-cost intersection configuration. Nevertheless, accessible traffic capacity models for mini-roundabouts do not exist. This study provides design recommendations and a simulation approach for capacity models of mini-roundabouts from USA data. Two typical geometries are selected that have a 24’ or 36’ approach widths typical of conventional intersections. The mini-roundabouts are best defined by the Inscribed Circle Diameter of 50’ and 75’. Mini-roundabouts are low-cost treatments using existing external boundaries of intersections. Field data are collected on Critical Gap and Headway acceptance for a similar design located in Stevensville, MD in order to calibrate a simulation. VISSIM Microsimulation software is used to model the selected prototype designs for capacity estimations. The defining feature for mini-roundabouts is the traversable central and splitter islands for large vehicles that make through or left turn movements. The linear capacity models presented, estimate the capacity of the mini-roundabouts to be lower than that of the single-lane roundabout. However the mini-roundabout has a higher capacity per square foot of land which would be an innovative solution for urban areas for increasing capacity at existing AWSC intersections at lower cost than single-lane roundabouts.
  Authors: Lochrane, Taylor W. P.; Kronprasert, Nopadon; Bared, Joe G.; Dailey, Daniel J.; Zhang, Wei
  Authors: Lochrane, Taylor W. P.; Kronprasert, Nopadon; Bared, Joe G.; Dailey, Daniel J.; Zhang, Wei
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-0209
  Practice-Ready: Yes
• Event-Based Modeling of Driver Yielding Behavior to Pedestrians at Two-Lane Roundabout Approaches
  Abstract: 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. Driver 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 driver 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 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 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 design speed), and can feasibly be incorporate into microsimulation algorithms to model driver yielding at roundabouts.
  Authors: Salamati, Katy; Schroeder, Bastian J.; Geruschat, Duane R.; Rouphail, Nagui M.
  Authors: Salamati, Katy; Schroeder, Bastian J.; Geruschat, Duane R.; Rouphail, Nagui M.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-0419
  Practice-Ready: Yes
• Evaluation of Roundabout Safety
  Abstract: While roundabouts are still fairly new in the U.S. and Wisconsin, their safety benefits have been studied with varied results. In this study, 24 roundabouts built in 2007 or before were analyzed for their safety performance. Three years of before and after crash data were gathered as well as geometric and traffic volume data. An empirical Bayes (EB) analysis was used to examine the safety benefits for total crashes and injury (K, A, B, C) crashes.The EB analysis was performed using the Safety Performance Functions (SPFs) from the Highway Safety Manual (HSM). Mixed results were found for total crash frequency but a significant decrease in crash severity was identified. Wisconsin roundabouts had an unbiased estimate of a 9.2 percent decrease in total crashes. National numbers similarly show decreases in total crashes. Wisconsin roundabouts showed a significant 52 percent decrease in injury crashes. Roundabouts nationwide are also experiencing a significant decrease in severe crashes.When evaluating predictors, the speed limit of the approaches did not show a significant impact on the safety of the roundabout. While multi-lane roundabouts seemed to be safer than single lane roundabouts when considering combined injury crashes, single lane roundabouts saw the largest decrease in total crashes. Two-way stop controlled (TWSC) intersection conversion to a roundabout had the highest safety benefit as compared to all-way stop controlled (AWSC) and signalized intersections.
  Authors: Qin, Xiao; Bill, Andrea R.; Chitturi, Madhav V.; Noyce, David A.
  Authors: Qin, Xiao; Bill, Andrea R.; Chitturi, Madhav V.; Noyce, David A.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-2060
  Practice-Ready: Yes
• Spatial and Temporal Analysis of Driver Gap Acceptance Behavior at Modern Roundabouts
  Abstract: Despite an increasing acceptance of modern roundabouts in the United States, there is still a widespread unfamiliarity with this type of intersection. This unfamiliarity results in more unpredictable gap acceptance decisions by drivers increasing the difficulty of design decisions. Here, the relationship between the spatial and temporal critical gaps accepted by drivers in modern roundabouts was explored via gap acceptance data taken on over 1,500 vehicle interactions at the roundabout on the University of Massachusetts Amherst campus. The critical gap was found to be 42 feet spatially and 2.2 seconds temporally, which correlated directly with the average speed of the circulating flow. An increase in critical gap time was observed for heavy vehicles in the traffic stream. While the unidirectional flow of the circulating traffic creates a potentially unpredictable environment for the driver, careful and precise analysis to obtain an accurate and reliable value of the critical gap will allow for improved design of future roundabouts.
  Authors: Abrams, Dan; Fitzpatrick, Cole D.; Tang, Yue; Knodler, Michael A.
  Authors: Abrams, Dan; Fitzpatrick, Cole D.; Tang, Yue; Knodler, Michael A.
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-3237
  Practice-Ready: Yes
• Analysis of Sight Distance, Crash Rate, and Operating Speed Relationships for Single-Lane Roundabouts in the United States
  Authors: Park, Seri
  Authors: Park, Seri
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1847
• Roundabout Design Practices: International Overview and Insights to Update the Italian Standard
  Authors: Montella, Alfonso
  Authors: Montella, Alfonso
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-2129
• Spatial and Temporal Analysis of Driver Gap Acceptance Behavior at Modern Roundabouts
  Authors: Abrams, Dan
  Authors: Abrams, Dan
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-3237
• Experimental Analysis and Methodological Approach by Microsimulation of Crossing-Speed Distribution on Small- and Large-Diameter Roundabouts
  Authors: Gallelli, Vincenzo
  Authors: Gallelli, Vincenzo
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-3787
• Roundabout Versus Traffic Signal Control: Comparative Analysis
  Authors: Wang, Zhao
  Authors: Wang, Zhao
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4422
• Study of Accommodating Oversize, Overweight Vehicles at Roundabouts
  Authors: Russell, Sr., Eugene
  Authors: Russell, Sr., Eugene
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4759
• Delay Analysis of Simulated Single-Lane Roundabout with Dedicated Bus/Truck Slip Lane
  Authors: Al-Ghandour, Majed
  Authors: Al-Ghandour, Majed
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-0151
• Calibration of VISSIM Roundabout Model: A Critical Gap and Follow-up Headway Approach
  Authors: Li, Zhixia
  Authors: Li, Zhixia
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1176
• Roundabout Networks for Robust, Walkable Communities
  Authors: VanElswyk, Abram
  Authors: VanElswyk, Abram
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1042
• Prediction of Capacity for Roundabouts Based on Percentages of Trucks in Entry and Circulating Flows
  Authors: Lee, Chris
  Authors: Lee, Chris
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-1391
• Evaluation of Roundabout Safety
  Authors: Qin, Xiao
  Authors: Qin, Xiao
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-2060
• Using Vehicle Simulations to Understand Needs and Strategies for Accommodating Oversize, Overweight Vehicles at Roundabouts
  Authors: Godavarthy, Ranjit Prasad
  Authors: Godavarthy, Ranjit Prasad
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4725
• Crash Severity Analysis at Roundabouts: Case Study in Quebec, Canada
  Authors: Burns, Shaun
  Authors: Burns, Shaun
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-4527
• Roundabout Design Practices: International Overview and Insights to Update the Italian Standard
  Abstract:

  The use of roundabouts improves intersection safety by eliminating or altering conflict types, reducing crash severity, and causing drivers to reduce speeds. However, previous studies have showed that poor geometric design can be a major contributory factor in crashes at roundabouts. Poor geometric design can result from inconsistencies in geometric design standard or the lack of standards.With the growing number of roundabouts internationally, several countries have recently updated their standards and guidelines. A review of the Australasian, EU and US standards and guidelines showed several inconsistencies within the Italian roundabout standard (and the standards used by other countries).. Several recommendations for improvement of the Italian standard have been proposed. These recommendations are mainly based on the concepts of design flexibility and performance based design. Indeed, rigid standards, which do not really take into account safety and operational consequences of the design decisions, and the need to balance opposing demands might produce undesirable outcomes.Finally, we would like to highlight the need for further research on the relationships between roundabout geometric design criteria, drivers’ behavior and safety.

  Authors: Montella, Alfonso; Turner, Shane Alan; Chiaradonna, Salvatore; Aldridge, Dave
  Authors: Montella, Alfonso; Turner, Shane Alan; Chiaradonna, Salvatore; Aldridge, Dave
  Year: 2013
  Document Type: Paper
  Subject: Design; Operations and Traffic Management; Safety and Human Factors
  Session: 542
  Paper Number: 13-2129