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With the increased prevalence of roundabouts in the United States, there is a need to evaluate the performance of roundabouts relative to other intersection control strategies. Few studies have compared roundabouts with other intersection control strategies in a systematic fashion. Consequently, this Thesis compares four types of intersection control strategies considering a single lane approach with a 58 km/hr speed limit and equal demand on all approaches. The study demonstrates that vehicle delay is minimized with the use of a roundabout intersection control for all demand levels below 500 veh/hr/approach. Above this point if the left turn percentage exceeds 70% traffic signal control is more efficient. The roundabout alternative also produces the fewest vehicle stops for low demand levels, low left turn demand and high right turn demand, however a TWSC alternative produces the least number of vehicle stops when the through and total demand is high. This study illustrates that fuel consumption and carbon dioxide, carbon monoxide, hydrocarbon and nitrogen oxide emissions can be improved with roundabout control over other intersection control strategies. The research presented here demonstrates that for low traffic demand levels roundabouts should be part of design alternatives considered for isolated intersection control. / Master of Science

This thesis reports on an investigation carried out to study the effect of flaring and turning movements on the performance of roundabout entries. A computer simulation program was developed to carry out the investigation. The model simulates an entry with two lanes at the approach section and four at the stop line. It can be modified easily to simulate straight entries by changing the input and one DATA statement. Data were collected at three public road sites at Sheffield to validate the model. A method of analysing the data was developed to obtain values of the gap-acceptance parameters. The values arrived at were used subsequently as input into the model to allow direct comparison of observed and simulated values. The comparison concluded that the model represents adequately the real conditions. The results produced showed that average delay for below-capacity operation is reduced by at least 40% when an entry is flared. Capacity improvement, measured as the effective number of lanes of a flared approach, is shown to be influenced by the circulating flow. There is an improvement of 50% for all studied casesfor circulating flow of 2300 veh/hr and more. Turning proportions do not affect capacity of straight entries but do affect that of flared entries. There is a difference of 25 - 30% between the extreme values depending on the proportion of left-turning vehicles. Turning proportions affect delays of both straight and flared entries. Minimum delay was obtained for combinations which include 30 - 40% left-turning proportion.

Roundabout installations are becoming common practice among DOTs and other local governments due to their superior safety attributes compared to other conventional at-grade intersections, especially stop-control and uncontrolled intersections. Current U.S. national guidelines for roundabout illumination recommend systematic illumination for all roundabouts. This recommendation might become a potential hindrance to desired widespread installations due to implied financial costs, especially in rural areas because the competing stop-control and uncontrolled intersections can be kept unlit. Interestingly rural roundabouts in most countries around the world are not illuminated as indicated by a recent survey of international roundabout illumination policies and standards from 45 countries. Also, review of intersection safety literature does not identify any publication that supports a systematic illumination policy of U.S. roundabouts. In fact, despite this recommendation there is no quantitative research on influence of illumination levels on nighttime safety at roundabouts and little on conventional intersections. Conversely, the literature shows a significant number of published studies which have indicated that currently recommended illumination levels on roadways can be reduced without compromising nighttime safety. This dissertation evaluates the link between roundabout crashes and different illumination levels. At the beginning of this dissertation research, there was no available repository of quantitative intersection illumination levels which could be used in highway safety research. Also, existing protocols for measurement require expensive light meters and are extremely time consuming to follow, making them impractical to use to study a large number of intersections. Consequently, this dissertation first evaluates the relationship with the best available data. The best available intersection illumination data was obtained from the Minnesota data contained in the Highway Safety Information System (HSIS). Minnesota crash and illumination data from 2003 to 2010 were analyzed. This illumination data was a qualitative description of intersection illuminating schemes and/or luminaire arrangement. Therefore, this dissertation also developed a cost-effective, accurate, and rapid method for measurement of quantitative intersection illumination data, and applied the developed protocol to a case study in Georgia. The measured intersection illumination was analyzed together with crash data obtained from GDOT for 2009 to 2014. The results of a naive analysis on the best available data indicated among other findings that the presence of lighting can provide approximately 61 percent lower total nighttime crash rate compared to the unlit condition. Also, providing illumination to the roundabout circle alone can yield about 80 percent of the benefits (55 percent reduction from unlit condition) of illuminating both the roundabout circle and approaches (66 percent reduction from unlit condition). Field test results for the camera calibration indicate that the average intersection illuminance derived from the protocol is within 4 percent difference of the actual average intersection illumination estimated from following the existing protocols. Next, despite limited roundabout data and potential issues of selection bias which could not be addressed in this dissertation, a cautious roundabout illumination specific crash modification factor was estimated with a negative binomial regression model. The model results showed that an increase of 1 lux in average roundabout illuminance will result in a 4.72 percent reduction in expected number nighttime crashes. The results of this work are useful in creating a sound framework for DOTs and other transportation agencies to determine the most appropriate level of illumination for roundabouts. This study also makes a number of significant contributions to highway safety research. First, this work is the first quantitative study on the impact of illumination on safety at roundabouts. The status-quo for highway safety research regarding the impacts of illumination had been to treat road lighting as a binary (Lit/Unlit) variable. However, even in most places without purposely-built road lighting there is usually ambient lighting from abutting facilities such as a gas stations or a store. Second, this dissertation is the first documented application of the photographic method to roundabouts. It is also the first documented application of the photographic method’s camera specific constant calibration approach to transportation field measurements. Previous documented application of the photographic method to transportation field measurements used an exposure specific calibration approach. Unlike the camera specific constant calibration approach, the exposure specific approach is rigid and field measurements must always be done at the exposure settings used in calibrating the camera. Thirdly, this work demonstrates the first developed procedure to developing uniformity (contour) plots from the photographic method. Next, this work can serve as the basis for initial efforts to create an illumination specific quantitative crash modification factor. Currently, the Highway Safety Manual is lacking in this important safety parameter. Last, but not the least this work offers procedures for collecting luminance data from the field and also documents a database of intersection illumination levels and intersection characteristics which can be used by future research.

Doctor of Philosophy / Department of Civil Engineering / Eugene Russell / It has been well documented that roundabouts can offer several safety and operational benefits over signalized and stop controlled intersection alternatives. However the growing use of roundabouts and their benefits could be greatly diminished because they may not be well designed for large trucks, or to accommodate oversize/overweight (OSOW) vehicles which may be essential to a state’s industry and economy. This dissertation addresses concepts to better design roundabouts for use by owners/operators of typical large trucks, and that will also accommodate OSOW vehicles where appropriate. Roundabout safety generally decreases with increased roundabout size, wider lanes and larger radii, the geometric parameters that benefit large trucks and OSOW, thus a better balance is needed. This study accomplishes this balance by initially reviewing and incorporating those portions of the study “Accommodating Oversize Overweight Vehicles at Roundabouts” that were researched, completed and written by the author of this dissertation, and which compiled current practice, research and concerns by various U.S. states and concerns of the trucking industry, by conducting four different surveys. Then to meet these concerns expressed by survey respondents, a great number of possible accommodation, strategies and design templates were developed by using existing design software. An evaluation method was also developed. Two additional, needed studies, not previously reported in any published literature, addressed : 1. a vertical, ground clearance analysis, and 2. a study of the use of roundabouts in urban freight networks to incorporate their inherent benefits ,such as, reducing congestion, delay and pollution. The first analysis described above was conducted by using software with 3D analysis capabilities to check and recommend critical vertical grades and maximum dimensions for a range of large truck types and OSOW vehicle configurations. Guidelines were developed to avoid problems of low, ground clearance vehicles scraping roundabout surfaces (“hanging up”). The second study used existing software that relates intersection types to intersection traffic flow efficiency and related pollution, on a number of routing scenarios to test the hypothesis that integration of roundabouts in these freight networks improves traffic flow, and decreases delay, congestion and pollution. The results were mixed but the procedure is sound and should be beneficial for future use by researchers and decision makers.

Modern roundabouts are increasingly being considered as a preferred intersection design within urban street networks in North America due, in large part, to the increased safety provided by roundabout. In the last decade, much research has been conducted in North America to quantify the performance of roundabouts in terms of vehicle delay as a function of vehicle traffic volume and roundabout geometry. In most jurisdictions, vehicles entering and existing the roundabout are required by law to yield right-of-way to pedestrians crossing the roundabout approach, and consequently, the presence of substantial pedestrian volumes are expected to degrade operational performance of the roundabout for vehicles. However, very little research has been conducted to estimate the impact that pedestrian volumes have on average vehicle delay. The aim of this research is to study the effects of pedestrian volume, entry traffic volume, and conflicting or circulating volume, on the delays that vehicles experience when traversing the roundabout. An analytical model is proposed to estimate vehicle delays on the basis of traffic flow and queuing theory. The model is applicable to single lane roundabouts. The model was calibrated and validated using vehicle delays obtained from the micro-simulation software, VISSIM (version 5.2) for a range of different conditions. The research described in this thesis demonstrates that pedestrian flows cause delays to vehicles traversing the roundabout in four distinct ways. Existing analytical techniques included within most design manuals consider only one of these sources of delays and consequently, conventional models typically under-estimate the impact that pedestrian flows have in terms of increasing delays to vehicles traversing the roundabout.

Road safety and traffic congestion are two of the critical issues facing the transportation profession today. As a means to promote safety and efficiency at United States intersections modern roundabouts are becoming more and more common. Over the last ten years, roundabouts implementation methodologies have been developed using data collected at U.S. roundabouts. These methodologies were first published in National Cooperative Highway Report 572: Roundabouts in the United States and more recently in the second edition of the national roundabout guidelines. This work attempts to validate the use of these methodologies for roundabouts in the state of Texas and also enhance guidelines for evaluating roundabout operations by exploring the effects of exiting flow, origin-destination patterns, and mean speed on roundabout entry-lane capacity. Capacity results from VISSIM are compared to the Highway Capacity Manual entry-lane capacity curve and results from SIDRA. / text

We design an Ordinary Delay Differential Equation model for car to car interaction with switching between four distinct force terms including "free acceleration'', "follow acceleration'', "follow braking'', and aggressive driving''. We calibrate this model by recreating a real experiment on spontaneous formation of traffic jams. Once simulations of our model match those of the experiment we develop a model of both intersections using traffic lights, and intersections using roundabouts. Using our calibrated car interaction model we compare traffic light versus roundabout efficiencies in both flux and fuel consumption. We also use simulation results to extract information relevant to macroscopic traffic models. A relationship between flux and density known as The Fundamental Diagram is derived, and we discuss a technique for comparing microscopic to macroscopic models. / Graduate / 0405 / gmcgrego@uvic.ca

Modern roundabouts are increasingly being considered as a preferred intersection design within urban street networks in North America due, in large part, to the increased safety provided by roundabout. In the last decade, much research has been conducted in North America to quantify the performance of roundabouts in terms of vehicle delay as a function of vehicle traffic volume and roundabout geometry. In most jurisdictions, vehicles entering and existing the roundabout are required by law to yield right-of-way to pedestrians crossing the roundabout approach, and consequently, the presence of substantial pedestrian volumes are expected to degrade operational performance of the roundabout for vehicles. However, very little research has been conducted to estimate the impact that pedestrian volumes have on average vehicle delay. The aim of this research is to study the effects of pedestrian volume, entry traffic volume, and conflicting or circulating volume, on the delays that vehicles experience when traversing the roundabout. An analytical model is proposed to estimate vehicle delays on the basis of traffic flow and queuing theory. The model is applicable to single lane roundabouts. The model was calibrated and validated using vehicle delays obtained from the micro-simulation software, VISSIM (version 5.2) for a range of different conditions. The research described in this thesis demonstrates that pedestrian flows cause delays to vehicles traversing the roundabout in four distinct ways. Existing analytical techniques included within most design manuals consider only one of these sources of delays and consequently, conventional models typically under-estimate the impact that pedestrian flows have in terms of increasing delays to vehicles traversing the roundabout.

<p>Trafiksystemet i Linköpings tätort bygger på två ringar, Y-ringen (yttre) och C- ringen (centrum), vilkas syfte är att avlasta stadens olika centrala delar. Den signalreglerade korsningen Industrigatan-Östgötagatan är en del av den så kallade Y-ringen och under vissa tider på dygnet finns det risk för köbildning. Antalet inkommande fordon i korsningen uppgick år 1999 till ca 28 000 per dygn och idag uppgår antalet till någonstansmellan 30 400-32 400 fordon/dygn. </p><p>Kommunen har planer på att på att etablera ett bostadsområde i Övre Vasastaden, vilket kan komma att påverka trafikmängderna i den studerade korsningen. En garanterad orsak till ökade trafikmängder är det faktum att Linköping ständigt ökar i invånarantal, med ökad folkmängd ökar även trafiken. Storleken på trafikökningen finns prognostiserad i olika trafikprognoser och dessa visar att när staden har 150 000 respektive 180 000 invånare kommer det inkommande flödet i aktuell korsning uppgå till ca 35 000 respektive ca 40 000 fordon/dygn. Framtida kö- och framkomlighetsproblem är därmed en realitet. </p><p>Med stöd av effektberäkningsprogrammet Capcal presenteras tre olika förslag på åtgärder där framkomlighetsproblemen undviks. Alternativ 1 innebär modifiering av trafiksignalerna och en förbjuden vänstersväng, alternativ 2 är en rund cirkulationsplats och alternativ 3 motsvaras av en oval cirkulationsplats. I de två sistnämnda alternativen föreslås även fyra alternativa lösningar för gång- och cykeltrafik. </p><p>En jämförelse mellan de olika alternativen visar att de ”bästa” effektmåtten erhålls vid alternativ 3 även om resultaten i alternativ 2 nästan är lika ”bra”. Däremot om kommunens prognoser skulle slå fel med 10 %, dvs om trafiken skulle öka med 10 % mer än beräknat, skulle endast alternativ 1 visa på godkända värden. Resonemanget kring rekommendationer av alternativ har delvis gjorts utifrån de framräknade effektmåtten men även med tanke på trafiksäkerheten för både de oskyddade trafikanterna och fordonstrafikanterna.</p>