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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
401

Att genom design effektivisera räddningsinsatsen för motorcyklister i trafikolycka

Vikström, John January 2012 (has links)
What if the emergency response directly knew exactly where to go and what to do if a road accident occured? During the last ten years the number of motorcyclists in Sweden has doubled. Every year, more than 300 riders are seriously injured and over 40 die in road accidents. Being found in time is critical to increase the chance of survival. The goal of this project is to use design methods to find a solution that enables a fast and adequate emergency response for motorcyclists and other unprotected road users. / Vad hade hänt om akutsjukvårdare direkt kände till var en olycka inträffat och vilken vårdinsats som behövdes? Under de senaste tio åren har antalet motorcyklister i Sverige fördubblats. Varje år skadas över 300 förare allvarligt, och över 40 omkommer i trafikolyckor. Att bli hittad i tid är kritiskt för att öka chansen för överlevnad. Målet med det här projektet är att med designmetoder hitta ett sätt att möjliggöra en snabb och adekvat räddningsinsats för motorcyklister och andra oskyddade motortrafikanter.
402

Riskkompensation hos dysforiska bilförare : en körsimulatorstudie

Lundqvist, Tomas January 2011 (has links)
Med fler än en miljon omkomna i trafikolyckor världen över varje år är trafiksäkerhet ett ständigt aktuellt område. Studier på deprimerade patienter har visat att negativ sinnesstämning medför försämrad körförmåga. Dessa effekter är i hög grad outforskade och det är därför viktigt att undersöka om de förekommer även vid en mildare grad av nedstämdhet, så kallad dysfori, vilket i så fall skulle innebära att negativ sinnesstämning i likhet med trötthet och alkoholpåverkan utgör en allvarlig trafikfara. För att bättre förstå hur sinnesstämning påverkar körförmåga är det dock också relevant att undersöka om dysfori kan bidra till riskkompensation, det fenomen som inträffar när människor kompenserar för säkerhetsförändringar genom ett förändrat riskbeteende. I denna uppsats beskrivs en del av en körsimulatorstudie kring dysfori och bilkörning, där syftet var att undersöka om dysfori kan vara en orsak till riskkompensation. 15 studenter vid Linköpings universitet delades upp i en testgrupp med dysforiska försöksdeltagare (N = 5) och en kontrollgrupp (N = 10) med hjälp av Major Depression Inventory, ett instrument för att diagnostisera depression. Dessa fick sedan genomföra en körning i simulatorn Desktop T&D där time headway, time to collision, genomsnittshastighet och antal omkörningar mättes för de olika grupperna för att undersöka förekomsten av riskkompensation. Resultatet visade att inga signifikanta skillnader kunde observeras för något av måtten. Riskkompensation har i många studier visat sig vara ett komplext fenomen att undersöka och ett flertal metodologiska problem förelåg, särskilt på grund av svårigheten att mäta risk i en simulator med god validitet. Det är dock viktigt att fortsatta undersökningar görs för att bättre förstå riskkompensation, samt att fenomenet beaktas som en tänkbar inverkande faktor i framtida studier av körförmåga.
403

Modelle zur Beschreibung des Geschwindigkeitsverhaltens auf Stadtstraßen und dessen Auswirkungen auf die Verkehrssicherheit auf Grundlage der Straßengestaltung / Speed models for urban roads - Predicting the choice of speed and its influence on traffic safety

Schüller, Hagen 28 September 2010 (has links) (PDF)
Die vorliegende Dissertationsschrift widmet sich der Beschreibung des Geschwindigkeits-verhaltens von Kraftfahrern auf innerörtlichen Straßen sowie dessen Auswirkungen auf die Verkehrssicherheit. Grundlage bilden manuelle und automatische Querschnittsmessungen von Einzelgeschwindigkeiten in Hauptverkehrs- und Erschließungs¬straßen mit zulässigen Höchstgeschwindigkeiten von 50 bzw. 30 km/h. Die Beschreibung von Wunschgeschwindigkeiten über unterschiedliche Abgrenzungen freifahrender Fahrzeuge, deren Geschwindigkeiten die Grundlage für die folgenden Modelle bilden, sowie die Überprüfung der Übertragbarkeit von Querschnittsmessungen auf die Strecke und die Analyse von Geschwindigkeitsganglinien dienen der Einordnung der in dieser Untersuchung vorgelegten Ergebnisse. Ziel des ersten Teils der Arbeit ist die Beschreibung möglicher Einflussfaktoren aus der Gestaltung, dem Betrieb sowie der Lage im Netz und dem Umfeld einer Straße auf die Wahl der Geschwindigkeit von Pkw-Fahrern. Erste Ansätze werden aus dem Vergleich von fahrtrichtungsbezogenen Geschwindigkeiten an einem Querschnitt mit asymmetrischer Gestaltung abgeleitet. Auf Basis querschnittsbezogener mittlerer und v85-Geschwindigkeiten werden verschiedene multiple Regressionsmodelle aufgestellt und miteinander verglichen. Die Modelle basieren auf Messungen im Straßennetz Dresdens und werden anhand von Messungen aus anderen deutschen Städten validiert. Signifikante Einflussgrößen ergeben sich aus den Bereichen Verkehrsbedeutung, Querschnittsgestaltung, Umfeldnutzung und Fahrbahnoberfläche eines Straßenquerschnitts. Die Einflussgrößen sowie deren Abhängigkeiten untereinander werden diskutiert und Potenziale für Maßnahmen zur Geschwindigkeitsreduzierung aufgezeigt. Im zweiten Teil der Arbeit werden für Tempo-50-Straßen verallgemeinerte lineare Modelle zur Beschreibung des Einflusses der Geschwindigkeit auf die Verkehrssicherheit abgeleitet. Für unterschiedliche Unfallkollektive bezüglich räumlicher Abgrenzung, Unfallschwere und Verkehrsbeteiligung wird der Geschwindigkeitseinfluss auf die Unfallzahl anhand einer Potenzfunktion (Power-Modell) unter Kontrolle der Randbedingungen Verkehrsaufkommen des motorisierten Individual-verkehrs und Umfeldnutzung beschrieben. Die Zahl der Unfälle mit Personenschaden steigt progressiv mit der mittleren Geschwindigkeit und degressiv mit dem DTV an. / Driving speeds of personal vehicles on urban roads are analyzed and their influence on traffic safety is modeled. The speed data is measured at cross sections on major and minor roads with speed limits of 50 and 30 km/h. Different kinds of classification of free-flow-vehicles were analyzed for the description of the desired speed of a driver. Also local speeds along road sections as well as time variation curves of driving speeds are documented in order to interpret and classify the provided findings. The first part of this work deals with the prediction of local driving speeds based on parameters of the roadway environment determining road design as well as the land-use next to the road. One first simple approach is to compare both driving directions at non-symmetric cross sections. Then several multiple regression models for mean speeds and 85-percentiles of the speed distribution are estimated and compared with each other. The models are based on the road network of the city of Dresden and are validated with speed measurements in other German cities. Road classification, cross section characteristics, land-use and the road surface condition are found to be significant parameters that correlate with driving speed. The possible influences on the choice of speed and their interdependencies as well as their practical relevance are discussed. In the second part of this work the influence of speeds on the occurrence of traffic accidents is estimated using Generalized Linear Models. This is done for different accident groups under consideration of the annual daily traffic and a parameter that describes the length and type of land-use of the adjacent buildings next to the road section. The relationship between speed and accident counts can be described using a power function. Accident numbers rise progressively with increasing speeds and rise in a declining manner with increasing amount of traffic.
404

Travel patterns and safety of school children in the eThekwini Municipality

Dhoda, Salma January 2009 (has links)
Submitted in fulfilment of the academic requirements for the degree of Magister Technologiae: Department of Civil Engineering and Surveying, Faculty of Engineering and the Built Environment, Durban University of Technology, 2009. / The annual incidence of pedestrian casualties on South African roads is approximately 34 000. This includes 4 000 deaths, 10 000 serious injuries and 20 000 minor injuries, costing the country an estimated R2,55 billion. A large number of injuries involve children and this is distressing but preventing this is a challenge. Statistics indicate that pedestrians are most at risk. School children have been identified as forming a considerable percentage of pedestrians. Consequently it is important to understand factors that influence children's travel patterns as an initial step toward reducing the accident rate. This study examines children's travel patterns at primary and secondary schools in the eThekwini area. In the absence of statistics regarding journeys to transport children to school, a questionnaire survey was designed to determine demographics, mode of travel to school, travel cost and duration, factors influencing choices of alternate modes of travel and problems experienced during school travel in terms of road safety. In addition, an on-site investigation was undertaken to assess the relevant engineering aspects including geometric design, traffic calming, signage and other traffic management aspects. This study focuses on scholar transport and discusses the findings of pilot and focal surveys. On analyzing the data, various problems were identified, namely: the road environment favours drivers over pedestrians, an absence of a formal travel plan, poor driver behaviour and an absence of dedicated school buses. A range of possible solutions is recommended. The recommendations focus on the Engineering, Enforcement and Evaluation aspects.
405

ES ir NVS šalių eismo saugumo politika, sprendžiant kelių eismo įvykių ir „juodųjų dėmių“ problemas: Lietuvos ir Rusijos atvejai / Road safety policy of the EU and the CIS countries in solving the problems of road traffic accidents and “accident black spots”: Lithuanian and Russian cases

Narkevič, Natalija 03 June 2014 (has links)
Magistro baigiamajame darbe nagrinėjama ES ir NVS kelių eismo saugumo politika, sprendžiant kelių eismo įvykių ir “juodųjų dėmių” problemas. Pasirinkti Lietuvos ir Rusijos atvejai. Pirmoje dalyje aptarta avaringumo problema šiuolaikiniame pasaulyje, pateikti statistiniai duomenys apie kelių eismo įvykiuose žuvusių žmonių skaičių ES ir NVS valstybėse, aptartos prevencinės priemonės, nurodytos kelių eismo įvykių ir „juodųjų dėmių“ atsiradimo priežastys Lietuvos ir Rusijos keliuose, pateiktos „juodųjų dėmių“ sąvokos bei jų nustatymo metodikos. Antroje dalyje nagrinėjami ES kelių transporto ir eismo saugumo reguliavimo teisiniai aspektai, nagrinėjami Lietuvos ir Rusijos svarbiausi kelių eismo saugumą reguliuojantys teisės aktai, analizuojama institucijų veikla bei finansavimas. / The master’s thesis covers the road safety policy of the EU and the CIS countries in solving the problems of road traffic accidents and “accident black spots”. The Lithuanian and Russian cases have been selected. Part One covers the discussion of the accident rate problem in a modern world, presentation of statistical data on the number of people, who died during the road traffic accidents in the EU and the CIS states, discussion of preventive measures, indication of the causes of road traffic accidents and “accident black spots” on Lithuanian and Russian roads, presentation of “accident black spots” terms as well as their identification methods. Part Two covers the analysis of legal aspects of the EU road transport and road safety regulation, fundamental legal acts governing traffic safety of Lithuania and Russia, as well as activities and financing of institutions.
406

Case studies of the transfer of road safety knowledge and expertise from western countries to Thailand and Vietnam, using an ecological road safety space model : elephants in traffic and rice cooker helmets

King, Mark Johann January 2005 (has links)
International organisations such as the World Health Organisation highlight the road crash problem in less motorised (or developing, or low income) countries like those in Southeast Asia and recommend the adoption of Western road safety measures. However, there are many differences between highly motorised and less motorised countries which raise questions about how successfully Western road safety knowledge and expertise can be transferred.----- A review of the statistical information on road crashes shows a great deal of uncertainty about both the scale and likely trajectory of road fatalities globally, in less motorised countries and in Asia. It is generally agreed, however, that Asia accounts for around half of all road fatalities, and analysis of the limited available data shows both that Southeast Asia is not an atypical region of Asia in road safety terms, and that Thailand and Vietnam are not atypical of Southeast Asian countries.----- A literature review of recommended practice approaches to road safety transfer in Asia shows that there are many economic, institutional, social and cultural factors which potentially influence the success of transfer. The review also shows that there is no coherent, comprehensive approach which either conceptualises these factors and their relationship to transfer outcomes, or uses an analysis of these factors to plan or modify transfer. To address this gap, this thesis develops a 'road safety space' model as a tool for conceptualisation and analysis, based on a biological metaphor which views the transfer of road safety measures from one context to another as analogous to the transfer of a species into a new ecological space. The road safety space model explicitly considers economic, institutional, social and cultural factors (from specific to broad) which influence the particular road safety issue which a particular road safety transfer effort seeks to address. A central contention of this thesis is that the road safety space model is both a feasible and useful tool to improve the process of road safety transfer to less motorised countries. Road safety space analysis is seen to have a role in a broader process of selection of road safety measures for transfer, along with knowledge of how the measures are considered to operate.----- The research reported in this thesis is comprised of three studies. Study 1 reviewed evaluations of road safety transfer to Thailand and Vietnam. Studies 2 and 3 were case studies of road safety transfer to Thailand and Vietnam respectively.----- Study 1 was an analysis of existing evaluations of road safety transfer to Thailand and Vietnam. The aims were to analyse the evaluations for their consideration of contextual factors, as described in the road safety space model, and to discuss whether the road safety space model assisted in understanding the reasons for success or failure of transfer. However, very few such evaluations exist, and those that were found generally lacked information on whether contextual factors were considered. This indicated the need for a more detailed, in-depth qualitative investigation of particular cases of road safety transfer, in order to investigate the feasibility and utility of the road safety space model.----- Two case studies (Study 2 and Study 3) were conducted to test whether the road safety space approach was both feasible and useful as a means of improving road safety transfer efforts. Study 2 was a case study of the development and implementation in Thailand of a road safety education program for school children, which involved the transfer of Western research and techniques. The transfer agents (i.e. those who effected the road safety transfer) were Australian consultants working for the Australian Road Research Board (ARRB). The transfer was funded by the World Bank and managed by the Thai Ministry of Education (MOE). Study 3 was a case study of the development and implementation of a motorcycle helmet wearing program in Vietnam, which involved the transfer of Western knowledge, techniques and technology. The transfer agents were staff of Asia Injury (AI), a non-government organisation (NGO), and the program was funded initially by a charitable fund, with the intention of becoming self-funding through operation of a helmet factory.----- The case studies employed background research into existing information on economic, institutional, social and cultural factors relevant to the road safety issues (road use behaviour of school children in Thailand and motorcycle helmet purchase and wearing in Vietnam), and collected data through interviews with key informants, analysis of secondary sources and observations. This information was used to derive the road safety space for each road safety issue, to identify the road safety space recognised and addressed by the transfer agents (ARRB and AI), and to determine which factors they missed, or were aware of but took no action on. The focus of this analysis was on the processes used in transfer, not on the road safety outcomes of transfer, although these provided information on the processes as well. Available evaluation information was used to draw links between the omissions and the success of the transfer processes. It was noted that information on how the transferred measures operate should come from a road safety space analysis in the originating country, although this raised questions about selection of country and time (when the measure was first introduced, or in its maturity).----- The feasibility and utility of the road safety space model were discussed. It was clear that the model provided information on the cases which was missed by the transfer agents. The questions examined next were whether this information could have been obtained from an exercise conducted before the transfer had commenced, whether the required effort and cost justified the potential benefits, and whether the information on the road safety space could have been useful for the transfer agents. Comparisons between the road safety spaces for the two cases showed some areas of commonality, e.g. perceptions of police corruption, but also many differences. It was considered likely that some broad factors could be generic, and the possibility was mooted that less motorised countries share issues with police enforcement. This requires further research, however, and at this stage it is better to treat each road safety space as a unique combination of contextual factors influencing the road safety issue of interest.----- It is concluded that the road safety space model is feasible if used in such a way as to minimise the research involved, and useful, although the degree of utility needs to be further explored in a prospective study. The limitation introduced by restricting informants to those who could speak English are discussed. An approach using road safety space analysis is recommended, emphasising analysis of the country to which the road safety measure is being transferred, supplemented by analysis of the originating country road safety space. Gaps in knowledge are identified for further research and development, in particular the theoretical and practical understanding of road use behaviours and their modification in less motorised countries in Southeast Asia. Elaboration of the model is also recommended, to take into account the influence of the type of measure transferred, the role of the transfer agent, the area of road safety (education, engineering or enforcement), and the time dimension (the time which might be needed for a transfer to show its effects).----- The findings of this research are likely to be applicable to road safety transfer in other less motorised regions of the world, however prospective testing is needed. They may also be relevant to issues of transfer for areas other than road safety, in particular public health and traffic engineering, where similar economic, institutional, social and cultural issues come together.
407

Population and genetic impacts of a 4-lane highway on black bears in eastern North Carolina

Nicholson, Jeremy Michael, January 2009 (has links)
Thesis (M.S.)--University of Tennessee, Knoxville, 2009. / Title from title page screen (viewed on Mar. 8, 2010). Thesis advisor: Frank T. van Manen. Vita. Includes bibliographical references.
408

Road Surface Preview Estimation Using a Monocular Camera

Ekström, Marcus January 2018 (has links)
Recently, sensors such as radars and cameras have been widely used in automotives, especially in Advanced Driver-Assistance Systems (ADAS), to collect information about the vehicle's surroundings. Stereo cameras are very popular as they could be used passively to construct a 3D representation of the scene in front of the car. This allowed the development of several ADAS algorithms that need 3D information to perform their tasks. One interesting application is Road Surface Preview (RSP) where the task is to estimate the road height along the future path of the vehicle. An active suspension control unit can then use this information to regulate the suspension, improving driving comfort, extending the durabilitiy of the vehicle and warning the driver about potential risks on the road surface. Stereo cameras have been successfully used in RSP and have demonstrated very good performance. However, the main disadvantages of stereo cameras are their high production cost and high power consumption. This limits installing several ADAS features in economy-class vehicles. A less expensive alternative are monocular cameras which have a significantly lower cost and power consumption. Therefore, this thesis investigates the possibility of solving the Road Surface Preview task using a monocular camera. We try two different approaches: structure-from-motion and Convolutional Neural Networks.The proposed methods are evaluated against the stereo-based system. Experiments show that both structure-from-motion and CNNs have a good potential for solving the problem, but they are not yet reliable enough to be a complete solution to the RSP task and be used in an active suspension control unit.
409

Vision-based moving pedestrian recognition from imprecise and uncertain data / Reconnaissance de piétons par vision à partir de données imprécises et incertaines

Zhou, Dingfu 05 December 2014 (has links)
La mise en oeuvre de systèmes avancés d’aide à la conduite (ADAS) basée vision, est une tâche complexe et difficile surtout d’un point de vue robustesse en conditions d’utilisation réelles. Une des fonctionnalités des ADAS vise à percevoir et à comprendre l’environnement de l’ego-véhicule et à fournir l’assistance nécessaire au conducteur pour réagir à des situations d’urgence. Dans cette thèse, nous nous concentrons sur la détection et la reconnaissance des objets mobiles car leur dynamique les rend plus imprévisibles et donc plus dangereux. La détection de ces objets, l’estimation de leurs positions et la reconnaissance de leurs catégories sont importants pour les ADAS et la navigation autonome. Par conséquent, nous proposons de construire un système complet pour la détection des objets en mouvement et la reconnaissance basées uniquement sur les capteurs de vision. L’approche proposée permet de détecter tout type d’objets en mouvement en fonction de deux méthodes complémentaires. L’idée de base est de détecter les objets mobiles par stéréovision en utilisant l’image résiduelle du mouvement apparent (RIMF). La RIMF est définie comme l’image du mouvement apparent causé par le déplacement des objets mobiles lorsque le mouvement de la caméra a été compensé. Afin de détecter tous les mouvements de manière robuste et de supprimer les faux positifs, les incertitudes liées à l’estimation de l’ego-mouvement et au calcul de la disparité doivent être considérées. Les étapes principales de l’algorithme sont les suivantes : premièrement, la pose relative de la caméra est estimée en minimisant la somme des erreurs de reprojection des points d’intérêt appariées et la matrice de covariance est alors calculée en utilisant une stratégie de propagation d’erreurs de premier ordre. Ensuite, une vraisemblance de mouvement est calculée pour chaque pixel en propageant les incertitudes sur l’ego-mouvement et la disparité par rapport à la RIMF. Enfin, la probabilité de mouvement et le gradient de profondeur sont utilisés pour minimiser une fonctionnelle d’énergie de manière à obtenir la segmentation des objets en mouvement. Dans le même temps, les boîtes englobantes des objets mobiles sont générées en utilisant la carte des U-disparités. Après avoir obtenu la boîte englobante de l’objet en mouvement, nous cherchons à reconnaître si l’objet en mouvement est un piéton ou pas. Par rapport aux algorithmes de classification supervisée (comme le boosting et les SVM) qui nécessitent un grand nombre d’exemples d’apprentissage étiquetés, notre algorithme de boosting semi-supervisé est entraîné avec seulement quelques exemples étiquetés et de nombreuses instances non étiquetées. Les exemples étiquetés sont d’abord utilisés pour estimer les probabilités d’appartenance aux classes des exemples non étiquetés, et ce à l’aide de modèles de mélange de gaussiennes après une étape de réduction de dimension réalisée par une analyse en composantes principales. Ensuite, nous appliquons une stratégie de boosting sur des arbres de décision entraînés à l’aide des instances étiquetées de manière probabiliste. Les performances de la méthode proposée sont évaluées sur plusieurs jeux de données de classification de référence, ainsi que sur la détection et la reconnaissance des piétons. Enfin, l’algorithme de détection et de reconnaissances des objets en mouvement est testé sur les images du jeu de données KITTI et les résultats expérimentaux montrent que les méthodes proposées obtiennent de bonnes performances dans différents scénarios de conduite en milieu urbain. / Vision-based Advanced Driver Assistance Systems (ADAS) is a complex and challenging task in real world traffic scenarios. The ADAS aims at perceiving andunderstanding the surrounding environment of the ego-vehicle and providing necessary assistance for the drivers if facing some emergencies. In this thesis, we will only focus on detecting and recognizing moving objects because they are more dangerous than static ones. Detecting these objects, estimating their positions and recognizing their categories are significantly important for ADAS and autonomous navigation. Consequently, we propose to build a complete system for moving objects detection and recognition based on vision sensors. The proposed approach can detect any kinds of moving objects based on two adjacent frames only. The core idea is to detect the moving pixels by using the Residual Image Motion Flow (RIMF). The RIMF is defined as the residual image changes caused by moving objects with compensated camera motion. In order to robustly detect all kinds of motion and remove false positive detections, uncertainties in the ego-motion estimation and disparity computation should also be considered. The main steps of our general algorithm are the following : first, the relative camera pose is estimated by minimizing the sum of the reprojection errors of matched features and its covariance matrix is also calculated by using a first-order errors propagation strategy. Next, a motion likelihood for each pixel is obtained by propagating the uncertainties of the ego-motion and disparity to the RIMF. Finally, the motion likelihood and the depth gradient are used in a graph-cut-based approach to obtain the moving objects segmentation. At the same time, the bounding boxes of moving object are generated based on the U-disparity map. After obtaining the bounding boxes of the moving object, we want to classify the moving objects as a pedestrian or not. Compared to supervised classification algorithms (such as boosting and SVM) which require a large amount of labeled training instances, our proposed semi-supervised boosting algorithm is trained with only a few labeled instances and many unlabeled instances. Firstly labeled instances are used to estimate the probabilistic class labels of the unlabeled instances using Gaussian Mixture Models after a dimension reduction step performed via Principal Component Analysis. Then, we apply a boosting strategy on decision stumps trained using the calculated soft labeled instances. The performances of the proposed method are evaluated on several state-of-the-art classification datasets, as well as on a pedestrian detection and recognition problem.Finally, both our moving objects detection and recognition algorithms are tested on the public images dataset KITTI and the experimental results show that the proposed methods can achieve good performances in different urban scenarios.
410

Predictable and Scalable Medium Access Control for Vehicular Ad Hoc Networks

Sjöberg Bilstrup, Katrin January 2009 (has links)
This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular ad hoc networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are channel access delay, number of consecutive packet drops and the distance between concurrently transmitting nodes. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience unbounded channel access delays and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several concurrently transmitting nodes are located close to each other. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both unpredictable and unfair besides the fact that it scales badly for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is predictable and fair. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure distance between concurrently transmitting nodes. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.

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