1,720,970 research outputs found
Effects of Charging Strategies and Policies on Electric Vehicles and Infrastructure From a Microscopic Perspective
Get PDFThe growing number of battery electric vehicles (BEV) implies changes in urban infrastructure. Large amounts of charging stations are to be built within few years to supply energy for a mostly electric vehicle fleet. In parallel the power grid has to be adapted to the growing energy demand. However charging behaviour depends on mobility patterns and which type of charging stations can be accessed. For example, charging at work is mostly restricted to employees and happens during working hours. Public charging stations cater any BEV user but take precious public space. In this work several charging station configurations for a city are studied on a microscopic level together with different BEV shares and charging strategies and policies. 24 hour working day SUMO microscopic traffic demand travels along trip chains and charges their electric vehicle battery when needed. Parking and charging infrastructure is limited to reasonable capacity for a medium sized German city. Then the configurations are evaluated with respect to charging station usage and the expected energy demand/supply of BEV for balanced and time-shift charging strategies as well as vehicle-to-home/vehicle-to-grid policies. Applying these strategies and policies on a large scale can lower the energy peak demand visibly
The State of Bicycle Modeling in SUMO
Get PDFMicroscopic traffic simulation tools provide ever-increasing value in the design and implementation of motor vehicle transport systems. Research and development of automated and intelligent technologies have highlighted the usefulness of simulation tools and develop-ment efforts have accelerated in recent years. However, the majority of traffic simulation soft-ware is developed with a focus on motor vehicle traffic and has limited capabilities in the sim-ulation of bicycles and other micro-mobility modes. Bicycles, e-bikes and cargo bikes represent a non-negligible modal share in many urban areas and their impact on the operation, efficiency and safety of traffic systems must be considered in any comprehensive study. The Differenti-ation between different types of micro-mobility modes, including microcars, e-kick scooters, different types of bicycles and other personal mobility devices, has not yet attracted enough attention in the development of simulation software which creates difficulties in including these modes in simulation-based studies. On November 25th, 2022, members of the SUMO team at DLR organized a workshop to assess the state of bicycle simulation in SUMO, identify short-comings and missing capabilities and prioritize the order in which bicycle traffic related features should be modified or implemented in the future. In this paper, different aspects of simulating bicycle traffic in SUMO are examined and an overview of the results of the workshop discus-sions is given. Some suggestions for the future development of SUMOemerging from this workshop,are presented as a conclusion
Effects of Charging Strategies and Policies on Electric Vehicles and Infrastructure From a Microscopic Perspective
Get PDFThe growing number of battery electric vehicles (BEV) implies changes in urban infrastructure. Large amounts of charging stations are to be built within few years to supply energy for a mostly electric vehicle fleet. In parallel the power grid has to be adpated to the growing energy demand. However charging behaviour depends on mobility patterns and which type of charging stations can be accessed. For example, charging at work is mostly restricted to employees and happens during working hours. Public charging stations cater any BEV user but take precious public space. In this work several charging station configurations for a city are studied on a microscopic level together with different BEV shares and charging strategies and policies. 24 hour working day SUMO microsopic traffic demand travels along trip chains and charges their electric vehicle battery when needed. Parking and charging infrastructure is limited to reasonable capacity for a medium sized German city. Then the configurations are evaluated with respect to charging station usage and the expected energy demand/supply of BEV for balanced and time-shift charging strategies as well as vehicle-to-home/vehicle-to-grid policies. Applying these strategies and policies on a large scale can lower the energy peak demand visibly
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Guiding automated vehicles by means of special signalised intersections
Get PDFAn städtischen signalisierten Knotenpunkten interagieren viele verschiedene Verkehrsteilnehmer miteinander, deren Wege sich kreuzen. Insbesondere Linksabbieger sind beim Durchsetzen durch den Gegenverkehr unfallgefährdet. Nach Jahrzehnten der Forschung erreichen inzwischen Fahrzeugprototypen ohne menschlichen Fahrer diesen öffentlichen Straßenraum. Bei verdeckter Sicht besteht die Gefahr, dass deren bordeigene Sensoren Konflikte mit anderen Verkehrsteilnehmern nicht rechtzeitig erkennen. Auch automatisierte Fahrzeuge stellt Linksabbiegen gegenüber anderen Fahraufgaben vor größere Herausforderungen, die von ihnen erhofften positiven Effekte auf die Verkehrssicherheit, den Verkehrsablauf und die Umwelt zu erreichen. Dabei lassen sich bedingt verträgliche Abbiegevorgänge durch eine andere Knotenpunktform und ein anderes Signalprogramm vermeiden. Neben einem vollständig verträglich signalisierten Knotenpunkt kommt eine Vorsortierung und Vorsignalisierung in Betracht: Die automatisierten Fahrzeuge bilden in der Zufahrt auf einem Vorsortierungsfahrstreifen einen Fahrzeugpulk und werden durch ein Vorsignal gemeinsam zum eigentlichen Knotenpunkt vorgelassen. Andere Fahrzeuge fahren analog auf ein zweites Vorsignal und kommen vor oder nach dem Pulk automatisierter Fahrzeuge am Hauptsignal an. Für die automatisierten Fahrzeuge kann dann eine Phase geschaltet werden, in der alle Fahrtrichtungen aus einer Zufahrt verträglich signalisiert sind, während zu anderen Zeiten andere Verkehrsteilnehmer bedingt verträglich signalisiert werden können. Inwiefern diese infrastrukturgebundenenMaßnahmen einen positiven Beitrag zur Einführung automatisierter Fahrzeuge in den städtischen Kontext leisten, steht im Fokus dieser Arbeit. Zum einen werden Auswirkungen auf die Verkehrssicherheit mithilfe von Surrogate Safety Measures abgeschätzt. Zum anderen wird beobachtet, wie sich die Verkehrsqualität nach Definition des Handbuchs für die Bemessung von Straßenverkehrsanlagen und die Kapazität von Knotenpunkten mit den Maßnahmen verändert. DieMaßnahmen werden anhand zweier Braunschweiger Beispielknotenpunkte unterschiedlicher Größe und Verkehrsnachfrage evaluiert. Zur Dimensionierung der Zufahrt wird ein analytisches Modell aufgestellt, das die Kapazität am Vorsignal und am Hauptsignal separat modelliert – denn ein überlasteter Vorsortierungsfahrstreifen beschränkt die Zufahrtskapazität. Stromabwärts wirken die Freigabezeiten an Vor- und Hauptsignal sowie die Aufstellfläche dazwischen als beschränkende Faktoren. Im Fall einer zweistreifigen Zufahrt begrenzt ab ca. 150 m Zufahrtslänge die Freigabezeit die Kapazität. Um die vielfältigen Wechselwirkungen zwischen den Verkehrsteilnehmern und der Infrastruktur zu berücksichtigen, werden die Beispielknotenpunkte mit ihrer näheren Umgebung in der mikroskopischen Verkehrssimulation SUMO abgebildet. Verglichen werden ein Nullfall ohne, einer mit automatisierten Fahrzeugen, ein Planfall mit zusätzlicher Vorsortierung und Vorsignalisierung und eine vollständig verträglich signalisierte Alternative. In bedingt verträglichen Verkehrsströmen nutzt das automatisierte Fahrzeug ein einfaches 2D-Sensormodell, um Unfälle zu vermeiden. 200 m vor dem Knotenpunkt melden sich die automatisierten Fahrzeuge an dessen Roadside Unit an. Die Vorsortierung und Vorsignalisierung wird sowohl als Festzeitsteuerung als auch in einer verkehrsabhängigen Variante untersucht. Ein großer Knotenpunkt mit mehreren mit Vorsortierung und Vorsignalisierung ausgestatteten Zufahrten fordert die nach den Richtlinien für Lichtsignalanlagen maximal mögliche Umlaufzeit von 120 s, um die Kapazität möglichst aufrechtzuerhalten. Jedoch reicht diese nicht aus, um werktägliche Verkehrsnachfragespitzen zu bedienen. Dies zeigt sich in mittleren Wartezeiten über 85 s und Rückstaus bis zum stromaufwärts gelegenen Knotenpunkt. Auch in der vollständig verträglich signalisierten Variante kann der Knotenpunkt nicht die komplette Referenzverkehrsnachfrage bedienen, erreicht aber eine höhere Kapazität. ImGegenzug warten Fußgänger aufgrund der gemeinsamen Freigabezeit für alle Furten geringfügig länger als mit Vorsortierung und Vorsignalisierung. Keine der untersuchten Varianten erfüllt somit die Ansprüche des Handbuchs für die Bemessung von Straßenverkehrsanlagen an signalisierte Knotenpunkte. In der Simulation werden die Verkehrskonflikte zwischensich kreuzenden Trajektorien quantitativ mit der Post-Encroachment Time bewertet. Werte unter 1 s deuten auf eine gefährliche Situation hin. Allerdings ähneln sich die Verteilungen über alle simulierten Fälle und zeigen nur sehr wenige Ausreißer im gefährlichen Wertebereich auf. Im Vergleich zum Nullfall beeinflusst die Vorsortierung und Vorsignalisierung die Verkehrssicherheit also nicht. Beide untersuchten Alternativen, wie Knotenpunkte an automatisierte Fahrzeuge angepasst werden können, führen zu einer niedrigeren Knotenpunktkapazität im Vergleich zum Nullfall. Damit einher geht eine nicht akzeptable Verkehrsqualität während Verkehrsnachfragespitzen. Da bereits der Nullfall als sicher eingestuft wird, bedarf es vorläufig keiner Umsetzung. Sollte sich dies ändern, wäre der vollständig verträglich signalisierte Knotenpunkt der Vorsortierung und Vorsignalisierung vorzuziehen.At urban signalised intersections, many road users interact when they cross each other’s path. Especially when turning left permissively, accidents with oncoming traffic are dangerous. After decades of development, the first prototype vehicles without human drivers enter the streets. These automated vehicles plan their trajectories based on the surroundings detected by their on-board cameras, Lidar and Radar devices. Occluded objects might lead to missing other road users. Compared to other driving tasks, automated vehicles are challenged by turning left and may struggle to achieve the expected positive effects on traffic safety, traffic quality and the environment. Instead, permissive turnings could be avoided by redesigning the intersection or only the signal program. Apart from converting all permissive turnings to protected ones, the so-called presorting and presignaling concept can be considered: Autonomous vehicles would queue upstream of the intersection at a dedicated presignal to enter the intersection as a kind of platoon. Other vehicles use a second presignal to advance before or after the automated vehicles to the intersection. As they have been separated from remaining traffic, automated vehicles can make use of a special signal phase with protected turnings only. Other road users in the same approach may still turn permissively, though. This thesis investigates whether the infrastructure measures described above help introducing automated vehicles in an urban context. Firstly, their impact on traffic safety is estimated using Surrogate Safety Measures compared to a base case. Changes in traffic quality and capacity at the intersection are monitored, also. They are graded according to the German standards of Handbuch für die Bemessung von Straßenverkehrsanlagen. Two characteristic intersections from Braunschweig (Germany) are chosen as examples to project presorting and presignaling facilities. The intersections differ significantly in size and traffic demand. As a first step, the approach capacity is studied by means of an analytic model. Depending on the number of automated vehicles and when they arrive, queues may prohibit vehicles from changing to their presorting lane. In that case, some approach capacity is lost. The expected capacity at the presignal is given as the weighted average of the queue spillback case and the case with free lane change. Downstream of the presignal, the green times and the storage size between the signals limit the capacity. For a two-lane approach example, capacity increases with the approach length until approximately 150 m, when it is limited by the green time. Road users interact with infrastructure elements and among themselves leading to numerous interdependencies. Consequently, the microscopic traffic simulation SUMO is chosen to model the example intersections and the road users’ behaviour. Three cases are defined to study the effects of automated driving and presorting and presignaling: A base case without automated vehicles nor changes to the infrastructure, one with automated vehicles added, one where presorting and presignaling is applied on top and another where instead all streams turn in a protected manner. Autonomous vehicles register with the Roadside Unit 200 m upstream of the intersection. When turning permissively, the automated vehicle uses a simple 2D sensor model to avoid accidents with oncoming traffic. Various design variants of presorting and presignaling signal programs are investigated. Big intersections with multiple presorting and presignaling facilities require the maximum cycle time of 120 s permitted by German traffic light guidelines RiLSA. Shorter cycle times would reduce the capacity. However, it is still not sufficient to serve a working day peak demand. Instead, average waiting times exceed 85 s and queues spill back to the intersection upstream. In comparison, intersections with protected turnings only provide a higher capacity but still not enough to serve the reference demand. Pedestrians have to wait longer with this design due to a single green time for all crossings. So none of the investigated options complies with the traffic quality requirements of the German guidelines Handbuch für die Bemessung von Straßenverkehrsanlagen. The traffic conflicts are evaluated quantitatively using Surrogate Safety Measures, Post-Encroachment Time in particular for crossing trajectories. Values below 1 s indicate dangerous situations. However the values are distributed very similarly across the simulated cases, showing very few outliers below the said threshold. Presorting and presignaling does not improve traffic safety compared to the base case. All examined variants to adapt intersections to automated vehicles lead to decreased capacities compared to the base case. Hence, the road users experience an unacceptable traffic quality during peak hour. Given the base case can already be classified as safe, there is no need to implement one of the variants. If this is proven wrong, intersections with protected turnings only shall be preferred over presorting and presignaling
Evaluation of a Signal State Prediction Algorithm for Car to Infrastructure Applications
No full textAbstractOne of the most relevant pieces of information for cooperative driver assistance systems based on car to infrastructure communication is the upcoming signal state at signalized intersections. For example, functions like Green Light Optimized Speed Advisory need a short term forecast of the switching times. Unfortunately, in case of vehicle actuated control these switching times cannot be easily determined and need to be estimated using probability theory. In this paper different driver assistance functions and their respective requirements on the precision of the prediction are discussed. In order to assess the reliability of existing prediction methods, a well-known algorithm based on Markov chains is evaluated using a microscopic simulation study. The internal Markov states are represented by combinations of signal states and corresponding detector counts. In the model which is used for simulation two existing urban intersections are considered: Whereas one of the intersections is characterized by public transport priority, the signal times at the other intersection are adapted with respect to private cars only. Based on the results of the simulation study the performance and the deficiencies of the known Markov-chain based prediction method are analyzed in order to derive starting points for the development of an extended approach which takes additional constraints into consideration. Both, the known and the extended prediction method are then evaluated with respect to the specific requirements of the driver assistance functions. Based on the evaluation conclusions are drawn and recommendations for the application of the methods are given
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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