Drivers need to make judgements of physical relationships related to driving speed, such as mean speed, risks, travel time and fuel consumption, in order to make optimal choices of vehicle speed. This is also the case for the general public, politicians and other stakeholders who are engaged in traffic issues. This thesis investigates how drivers’ judgements of travel time (Study I and II), fuel consumption (Study III) and mean speed (Study IV) relate to actual physical measures. A cognitive time-saving bias has been found in judgements of travel time. The time saving bias implies that people overestimate the time saved when increasing speed from a high speed and underestimate the time saved when increasing speed from a low speed. Previous studies have mainly investigated the bias from a cognitive perspective in questionnaires. In Study I the bias was shown to be present when participants were engaged in a driving simulator task where participants primarily rely on perceptual cues. Study II showed that intuitive time saving judgements can be debiased by presenting drivers with an alternative speedometer that indicate the inverted speed in minutes per kilometre. In Study III, judgements of fuel consumption at increasing and decreasing speeds were examined, and the results showed systematic deviations from correct measures. In particular, professional truck drivers underestimated the fuel saving effect of a decrease in speed. Study IV showed that subjective mean speed judgements differed from objective mean speeds and could predict route choice better than objective mean speeds. The results indicate that biases in these judgements are robust and that they predict behaviour. The thesis concludes that judgements of mean speeds, time savings and fuel consumption systematically deviate from physical measures. The results have implications for predicting travel behaviour and the design of driver feedback systems. / Förare bör göra bedömningar som relaterar till hastighet, såsom bedömningar av medelhastighet, risk, restid och bränsleåtgång. Dessa bedömningar är nödvändiga för att föraren ska kunna välja en optimal hastighet, men också för att allmänheten, politiker och andra intressenter som är involverade i trafikfrågor ska kunna fatta välgrundade beslut. Denna avhandling består av fyra delstudier där förares bedömningar av restid (Studie I och II), bränsleåtgång (Studie III) och medelhastighet (Studie IV) studeras i relation till faktiska fysikaliska mått. Tidigare enkätstudier har påvisat ett kognitivt bias i tidsvinstbedömningar vid höga och låga hastigheter som påverkar mänskligt beteende. Studie I visade att detta bias också förekommer i en primärt perceptuell motorisk uppgift där förarna i studien kör i en körsimulator. Studie II visade att dessa intuitiva tidsbedömningar kan förbättras genom att köra med en alternativ hastighetsmätare i bilen som indikerar den inverterade hastigheten i minuter per kilometer istället för hastigheten i kilometer per timme. I Studie III undersöktes bedömningar av bränsleåtgång vid hastighetsökningar och hastighetssänkningar, och resultaten visar att bedömningarna systematiskt avviker från faktisk bränsleåtgång. Ett intressant resultat var att lastbilsförare i allmänhet underskattade bränslebesparingen som kan göras till följd av en hastighetssänkning. Studie IV visade att subjektiva bedömningar av medelhastighet som avviker från objektiva medelhastigheter kan predicera vägval, vilket tyder på att systematiska fel i dessa bedömningar är robusta och kan predicera vägval. Sammanfattningsvis visar avhandlingen hur bedömningar av medelhastighet, tidsvinst och bränsleåtgång systematiskt avviker från fysikaliska mått. Resultaten har betydelse för modellering av resebeteende och design av förarstödssystem. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted.</p>

Drivers need to make judgements of physical relationships related to driving speed, such as mean speed, risks, travel time and fuel consumption, in order to make optimal choices of vehicle speed. This is also the case for the general public, politicians and other stakeholders who are engaged in traffic issues. This thesis investigates how drivers’ judgements of travel time (Study I and II), fuel consumption (Study III) and mean speed (Study IV) relate to actual physical measures. A cognitive time-saving bias has been found in judgements of travel time. The time saving bias implies that people overestimate the time saved when increasing speed from a high speed and underestimate the time saved when increasing speed from a low speed. Previous studies have mainly investigated the bias from a cognitive perspective in questionnaires. In Study I the bias was shown to be present when participants were engaged in a driving simulator task where participants primarily rely on perceptual cues. Study II showed that intuitive time saving judgements can be debiased by presenting drivers with an alternative speedometer that indicate the inverted speed in minutes per kilometre. In Study III, judgements of fuel consumption at increasing and decreasing speeds were examined, and the results showed systematic deviations from correct measures. In particular, professional truck drivers underestimated the fuel saving effect of a decrease in speed. Study IV showed that subjective mean speed judgements differed from objective mean speeds and could predict route choice better than objective mean speeds. The results indicate that biases in these judgements are robust and that they predict behaviour. The thesis concludes that judgements of mean speeds, time savings and fuel consumption systematically deviate from physical measures. The results have implications for predicting travel behaviour and the design of driver feedback systems. / Förare bör göra bedömningar som relaterar till hastighet, såsom bedömningar av medelhastighet, risk, restid och bränsleåtgång. Dessa bedömningar är nödvändiga för att föraren ska kunna välja en optimal hastighet, men också för att allmänheten, politiker och andra intressenter som är involverade i trafikfrågor ska kunna fatta välgrundade beslut. Denna avhandling består av fyra delstudier där förares bedömningar av restid (Studie I och II), bränsleåtgång (Studie III) och medelhastighet (Studie IV) studeras i relation till faktiska fysikaliska mått. Tidigare enkätstudier har påvisat ett kognitivt bias i tidsvinstbedömningar vid höga och låga hastigheter som påverkar mänskligt beteende. Studie I visade att detta bias också förekommer i en primärt perceptuell motorisk uppgift där förarna i studien kör i en körsimulator. Studie II visade att dessa intuitiva tidsbedömningar kan förbättras genom att köra med en alternativ hastighetsmätare i bilen som indikerar den inverterade hastigheten i minuter per kilometer istället för hastigheten i kilometer per timme. I Studie III undersöktes bedömningar av bränsleåtgång vid hastighetsökningar och hastighetssänkningar, och resultaten visar att bedömningarna systematiskt avviker från faktisk bränsleåtgång. Ett intressant resultat var att lastbilsförare i allmänhet underskattade bränslebesparingen som kan göras till följd av en hastighetssänkning. Studie IV visade att subjektiva bedömningar av medelhastighet som avviker från objektiva medelhastigheter kan predicera vägval, vilket tyder på att systematiska fel i dessa bedömningar är robusta och kan predicera vägval. Sammanfattningsvis visar avhandlingen hur bedömningar av medelhastighet, tidsvinst och bränsleåtgång systematiskt avviker från fysikaliska mått. Resultaten har betydelse för modellering av resebeteende och design av förarstödssystem. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted.</p>

Older adults are at an increased risk for motor-vehicle collisions (MVCs) once distance driven is considered, a finding that is partly attributed to a decline in attention related processes associated with age. MVCs typically occur in highly specific areas, suggesting a role of the complexity of the driving environment contributing to the occurrence of MVCs. The goal of this thesis was to explore the attentional demands of simulated driving events of varying complexity among young, mature and older drivers. In the present studies, attentional demand associated with driving was assessed through the peripheral detection task (PDT), a method in which a stimulus unrelated to the driving task is presented and drivers manually respond immediately upon its detection; latency to respond is recorded. The complexity of the driving environment was operationalized in terms of vehicle handling and of information processing elements. In the first study, inexperienced drivers completed a series simulated driving scenarios that varied according to their information processing and vehicle handling demands. The results showed a reduction in PDT performance at intersections where information processing is increased as well as when handling maneuvers behind a lead vehicle were required. Building on these findings, the second study employed the identical protocol as the first but examined differences in attentional demand between mid-aged and older drivers. The results indicated that when information processing demands were increased through the addition of traffic, and buildings, all participants exhibited greater workload regardless of age. The third study presented young, mid-aged, and older drivers with a simulated driving assessment course and administered several cognitive tasks. The results of the third study supported the hypothesis in that complex driving situations elicited greater attentional demand among drivers of all ages. Older adults showed greater attentional demand in comparison to young and mid-aged adults even after controlling for baseline response time. Older drivers also scored poorer on a global measure of driving safety. The results of this thesis highlight the roles of intrinsic and extrinsic factors involved in safe driving and are discussed in terms of appropriate interventions to improve road safety.

Das Projekt „Entwicklung eines elektronischen Informations- und Lernprogramms zum Arbeitsschutz für Berufskraftfahrerinnen und -fahrer im Fernverkehr“ befasst sich mit Fragen der Lernwirksamkeit und der beruflichen Integrationsfähigkeit von mobilen Lernangeboten für Berufskraftfahrer. Ausgehend von der Problematik der zunehmend älter werdenden Arbeitnehmer und der Notwendigkeit deren Arbeitskraft langfristig zu erhalten, werden Lerninhalte zum Arbeits- und Gesundheitsschutz mediendidaktisch aufbereitet und den Berufskraftfahrern auf einer Lernplattform zur Verfügung gestellt. Per Netbook und UMTS-Verbindung greifen die Fahrer zeit- und ortsunabhängig auf die Lerneinheiten zu und beantworten entsprechende Wissensfragen. Erste Ergebnisse konnten bereits im Rahmen eines Lernmaterialtests gewonnen werden, wohingegen der Usability-Test sich derzeit noch in der Auswertung befindet.

Nominally, one can expect any user of modern technology to at least carry a handheld device of the class of an iPAQ (perhaps in the form of a cellphone). The availability of technology in the environment (home, office, public spaces) also continues to grow at an amazing pace. With advances in technology, it is feasible to remain connected and enjoy services that we care about, be it entertainment, sports, or plain work, anytime anywhere. We need a system that supports seamless migration of services from handhelds to the environment (or vice versa) and between environments. Virtualization technology is able to support such a migration by providing a common virtualized interface on both source and destination. In this dissertation, we focus on two levels of virtualization to address issues for seamless mobility. We first identify three different kinds of spaces and three axes to support mobility in these spaces. Then we present two systems that address these dimensions from different perspectives. For middleware level virtualization, we built a system called MobiGo that can capture the application states and restore the service execution with saved states at the destination platform. It provides the architectural elements for efficiently managing different states in the different spaces. Evaluation suggested that the overhead of the system is relatively small and meets user's expectation. On the other hand, for device level virtualization, Chameleon is a Xen-like system level virtualization system to support device level migration and automatic capability adaptation at a lower level. Chameleon is able to capture and restore device states and automatically accommodate the heterogeneity of devices to provide the migration of services. Device level virtualization can address some issues that cannot be addressed in middleware level virtualization. It also has less requirements than middleware level virtualization in order to be applied to existing systems. Through performance measurements, we demonstrate that Chameleon introduces minimal overhead while providing capability adaptation and device state migration for seamless mobility in ubiquitous computing environments.

Drivers are expected to traverse through an intersection in malfunctioning flash mode in the same manner as a stop-sign controlled intersection. Red/red flash corresponds to four-way stop control and yellow/red flash corresponds to two-way stop control. However, at a red flashing signal there is no assurance that a driver can see the cross street indication (i.e., yellow or red flash) and therefore does not know if the intersection is operating as a two-way or four-way flash. In addition, some drivers appear unclear on the rules at a flashing signal. This confusion makes the intersection more accident prone. This study builds upon several previous studies, using data extracted from existing files. The objective of this study is to determine the level of drivers' understanding of the flash control through an analysis of violation rates and types at recorded intersection in malfunction flash. Comparing these violation rates to those at comparable stop-control intersections will help illustrate the difference in drivers' understanding of these similar intersection control devices.

Unlicensed driving remains a serious problem for road safety, despite ongoing improvements in traffic law enforcement practices and technology. While it does not play a direct causative role in road crashes, unlicensed driving undermines the integrity of the driver licensing system and is associated with a range of high-risk behaviours. This thesis documents three studies that were undertaken to explore the scope and nature of unlicensed driving, in order to develop more effective countermeasures to the behaviour.----- Study One utilised official road crash data from the Australian state of Queensland to compare the crash involvement patterns of unlicensed drivers with those of licensed drivers. The results confirmed that unlicensed driving is a relatively small, but significant road safety problem. Unlicensed drivers represent over 6% of the drivers involved in fatal crashes and 5% of those in serious injury crashes. Based on a quasi-induced exposure method, unlicensed drivers were found to be almost three times as likely to be involved in a crash than licensed drivers. In the event of a crash, those involving unlicensed drivers were twice as likely to result in a fatality or serious injury. Consistent with these results, the serious crashes involving unlicensed drivers were more likely to feature risky driving behaviours, such as drink driving, speeding and motorcycle use, than those involving licensed drivers.----- Study Two involved a cross-sectional survey of 309 unlicensed driving offenders who were recruited at the Brisbane Central Magistrates Court. The survey involved a face-to-face interview that took approximately 25 minutes to complete and achieved a response rate of 62.4%. A wide range of offenders participated in the study, including: disqualified and suspended drivers; expired licence holders; drivers without a current or appropriate licence; and those who had never been licensed. The results reinforced concerns about the on-road behaviour of unlicensed drivers. Almost one quarter of all the offenders reported driving unlicensed when they thought they might have been over the alcohol limit. Similarly, 25% reported exceeding the speed limit by 10 km/h or more on most or all occasions, while 15% admitted that they didn't always wear their seat belt. In addition, the results indicated that unlicensed drivers should not be viewed as a homogeneous group. Significant differences were found between the offender types in terms of their socio-demographic characteristics (age, education level, prior criminal convictions); driving history (prior convictions for unlicensed driving and other traffic offences); whether they were aware of being unlicensed; the degree to which they limited their driving while unlicensed; and their drink driving behaviour. In particular, a more deviant sub-group of offenders was identified, that included the disqualified, not currently licensed and never licensed drivers, who reported higher levels of prior criminal offending, alcohol misuse and self-reported drink driving. The results of Study Two also highlight the shortcomings of existing police enforcement practices. Almost one-third of the sample reported that they continued to drive unlicensed after being detected by the police (up until the time of the court hearing), while many offenders reported experiences of punishment avoidance. For example, over one third of the participants reported being pulled over by the police while driving unlicensed and not having their licence checked.----- Study Three involved the further analysis of the cross-sectional survey data to explore the factors contributing to unlicensed driving. It examined the influence of various personal, social and environmental factors on three aspects of the offenders' behaviour: the frequency of their driving while unlicensed; whether they continued to drive unlicensed after being detected; and their intentions to drive unlicensed in the future. This study was also designed to assess the capacity of a number of different theoretical perspectives to explain unlicensed driving behaviour, including deterrence theory and Akers' (1977) social learning theory. At an applied level, the results of Study Three indicated that personal and social factors exert the strongest influence over unlicensed driving behaviour. The main personal influences on unlicensed driving were: the need to drive for work purposes; exposure to punishment avoidance; personal attitudes to unlicensed driving; and anticipated punishments for the behaviour. The main social influences reflected the social learning construct of differential association, namely being exposed to significant others who both engage in unlicensed driving (behavioural dimension) and hold positive attitudes to the behaviour (normative dimension). At a theoretical level, the results of Study Three have two important implications for traffic psychology and criminology. Firstly, they provided partial support for Stafford and Warr's (1993) reconceptualisation of deterrence theory by demonstrating that the inclusion of punishment avoidance can improve the overall predictive utility of the perspective. Secondly, they suggested that social learning theory represents a more comprehensive framework for predicting illegal driving behaviours, such as unlicensed driving. This is consistent with Akers' (1977; 1990) assertion that formal deterrence processes can be subsumed within social learning theory.----- Together, the results of the three studies have important implications for road safety. Most importantly, they question the common assumption that unlicensed drivers drive in a more cautious manner to avoid detection. While the findings indicate that many offenders reduce their overall driving exposure in order to avoid detection, this does not appear to result in safer driving. While it remains possible that unlicensed drivers tend to act more cautiously than they would otherwise, it appears that their driving behaviour is primarily designed to reduce their chances of detection. In terms of countermeasures, the research indicates that a multi-strategy approach is required to address the problem of unlicensed driving. Unlicensed drivers do not represent a homogeneous group who are likely to be influenced by the threat of punishment alone. Rather, innovative strategies are required to address the wide range of factors that appear to encourage or facilitate the behaviour. Foremost among these are punishment avoidance and the need to drive for work purposes.

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Τα τελευταία δεκαπέντε χρόνια έχει προχωρήσει σημαντικά η ανάπτυξη αυτομάτων συστημάτων βοήθειας του οδηγού που στοχεύουν να προειδοποιήσουν για το περιβάλλον οδήγησης και τις πιθανότητες σύγκρουσης με άλλα οχήματα. Τα Πανεπιστήμια, Κρατικοί φορείς και αυτοκινητοβιομηχανίες ρίχνουν ιδιαίτερο βάρος στο θέμα αυτό που έχει κοινωνικές και εμπορικές διαστάσεις. • Κοινωνικές διαστάσεις γιατί η αξιόπιστη λειτουργία συστημάτων βοήθειας οδηγών μπορεί να συμβάλλει αποφασιστικά στη μείωση των τροχαίων ατυχημάτων. • Εμπορικές διαστάσεις γιατί ο ανταγωνισμός των βιομηχανιών αυτοκινήτων σε συνεργασία με εταιρείες παραγωγής συστημάτων αυτοματισμού, οδηγεί σε ένα κυνήγι παρουσίασης πλέον σύγχρονων και «ελκυστικών» συστημάτων για το καταναλωτικό κοινό. Ειδικά στο θέμα των κοινωνικών διαστάσεων, τα παρακάτω στοιχεία δίνουν με πολύ έμφαση το μέγεθος του προβλήματος. Κατά μέσον όρο, τουλάχιστον ένας άνθρωπος πεθαίνει κάθε λεπτό σε τροχαίο ατύχημα. Τα τροχαία ατυχήματα επίσης τραυματίζουν τουλάχιστο 10 εκατομμύρια ανθρώπους, από τους οποίους 2 ή 3 εκατομμύρια σοβαρά. Προβλέπεται ότι οι νοσοκομειακές δαπάνες, οι κατεστραμμένες περιουσίες και άλλα παρεμφερή κόστη θα ανέλθουν στο 1–3 % του παγκοσμίου ακαθαρίστου εθνικού προϊόντος. Αντικείμενο της διπλωματικής εργασίας είναι η μελέτη 26 ερευνητικών εργασιών που ερευνούν διατάξεις εντοπισμού και ανίχνευσης οχημάτων, πεζών, αντικειμένων και οδικών υποδομών, η σύγκριση της μεθοδολογίας τους, ο σχολιασμός πλεονεκτημάτων και μειονεκτημάτων και η αναφορά σε μελλοντικές απαιτήσεις - προκλήσεις. Η δομή της εργασίας είναι η παρακάτω: • Στο κεφάλαιο Ι γίνεται εισαγωγή στο αντικείμενο της εργασίας και παρουσιάζεται σειρά στατιστικών δεδομένων για τα τροχαία ατυχήματα. • Στο κεφάλαιο II γίνεται συνοπτική παρουσίαση των ερευνητικών εργασιών που χρησιμοποιήθηκαν για την παρουσίαση του θέματος. • Στο κεφάλαιο III γίνεται παρουσίαση βασικών στοιχείων εξοπλισμού για τον εντοπισμό και παρακολούθηση του κυκλοφοριακού τοπίου καθώς επίσης αναφορά σε θεωρητικές υπολογιστικές επεξεργασίες. • Στο κεφάλαιο IV γίνεται μια παρουσίαση βασικών ερευνητικών και πειραματικών διατάξεων που έχουν προταθεί ή εφαρμοσθεί για τον εντοπισμό, την ανίχνευση και παρακολούθηση οχημάτων, πεζών, εμποδίων επί των οδών, και υποδομών παραπλεύρως του οδικού δικτύου, έτσι ώστε να παράγεται πληροφορία στον χρήστη της οδού. Πληροφορία που μπορεί να αποδειχθεί από χρήσιμη μέχρι σωτήρια γιατί μπορεί να λειτουργήσει είτε ως προειδοποίηση στον οδηγό είτε ως ερέθισμα για αυτόματη επενέργεια επί των συστημάτων του αυτοκινήτου (π.χ. αυτόματο φρενάρισμα). • Στο κεφάλαιο V γίνεται σχολιασμός και συγκρίσεις των περιγραφεισών μεθόδων, εξάγονται συμπεράσματα και επισημαίνονται κάποιες μελλοντικές ερευνητικές και κατασκευαστικές προκλήσεις. • Στο κεφάλαιο VI αναφέρεται η χρησιμοποιηθείσα βιβλιογραφία. Όλες οι μέθοδοι προσπαθούν να ανταποκριθούν μερικά ή ολικά στα παρακάτω ζητούμενα: ◊ Εντοπισμός στόχων (κινητών και ακινήτων). ◊ Παρακολούθηση συμπεριφοράς κινουμένων στόχων. ◊ Παραγωγή προειδοποίησης (ακουστικά ή οπτικά σήματα). ◊ Αυτόματη επενέργεια σε συστήματα του οχήματος. • Εργαλεία των συστημάτων που παρουσιάζονται είναι συνήθως ένα σύνολο εξοπλισμού παθητικών και ενεργητικών αισθητήρων, ένας πρωτότυπος αλγόριθμος επεξεργασίας των στοιχείων και ένας υπολογιστής για την επεξεργασία και αξιολόγηση των δεδομένων. • Εμπόδια που πρέπει να υπερπηδηθούν είναι η συνθετότητα του περιβάλλοντος οδήγησης (αυτοκινητόδρομοι, επαρχιακοί οδοί, αστικό οδικό δίκτυο κ.λ.π.) και οι μεταβαλλόμενες καιρικές συνθήκες (καλοκαιρία, βροχή, ομίχλη, χιόνι κ.λ.π.). • Κλειδί στην αποτελεσματικότητα είναι η συλλογή των πλέον επίκαιρων δεδομένων και η δημιουργία γρήγορου και στιβαρού αλγόριθμου. • Μέτρο επιτυχίας είναι η συμπεριφορά σε πραγματικές συνθήκες και η δυνατότητα λειτουργικής και οικονομικής ενσωμάτωσης στο όχημα. Οι μελετηθείσες 26 ερευνητικές εργασίες που εντοπίζουν και ανιχνεύουν κατηγοριοποιούνται: 1. Ανάλογα με τον χρησιμοποιούμενο εξοπλισμό Α. Σε διατάξεις απλών ενεργητικών αισθητήρων Β. Σε διατάξεις παθητικών αισθητήρων (οπτικά συστήματα με διάφορες μορφές καμερών) Γ. Σε διατάξεις δυο ειδών αισθητήρων Δ. Σε πολυαισθητηριακές διατάξεις Σημειώνουμε ότι παρουσιάζονται δυο κατηγορίες αισθητήρων: οι ενεργητικοί και οι παθητικοί. Ενεργητικοί αισθητήρες θεωρούνται οι τύπου ραντάρ (mm κύμα), τύπου laser (lidar και scanners) και οι ακουστικού τύπου. Οπτικοί αισθητήρες, όπως συνήθεις κάμερες, θερμογραφικές κάμερες (FLIR - Forward Looking InfraRed), CCD κάμερες (Charge-coupled device cameras) συχνά αναφέρονται ως παθητικοί αισθητήρες γιατί αποκτούν δεδομένα χωρίς παρέμβαση. Αναλύονται τα ιδιαίτερα χαρακτηριστικά των παραπάνω διατάξεων, τα πλεονεκτήματα και τα μειονεκτήματά τους και αναδεικνύεται η επικρατούσα, με την πάροδο του χρόνου, τάση συνδυασμού διαφόρων αισθητήρων. 2. Ανάλογα με τις στοχεύσεις, τους υπολογιστικούς αλγορίθμους και τα ιδιαίτερα χαρακτηριστικά τους. Οι εξετασθείσες μελέτες που εντοπίζουν και παρακολουθούν στόχους του κυκλοφοριακού τοπίου μπορούν να ταξινομηθούν ως προς τους στόχους στις εξής κατηγορίες: 1. Κινούμενα οχήματα – πεζοί (κυρίως αστικό κυκλοφοριακό τοπίο). 2. Κινούμενα οχήματα (αυτοκινητόδρομοι, επαρχιακοί οδοί, αστικές οδοί). 3. Στάσιμα αντικείμενα, οχήματα – πεζοί (αυτοκινητόδρομοι, επαρχιακοί οδοί, αστικές οδοί). 4. Πεζοί (αστικό κυκλοφοριακό τοπίο). 5. Οδικές υποδομές (αυτοκινητόδρομοι) με έμφαση στις κατακόρυφες ταμπέλες και στις ανισόπεδες διαβάσεις. Από την παρουσίαση και τη σύγκριση των εργασιών, προκύπτει ότι το βασικό πρόβλημα που γίνεται προσπάθεια να αντιμετωπιστεί, είναι η εγκατάσταση διατάξεων που θα πρέπει να διακρίνονται, μεταξύ άλλων, από: • Αξιοπιστία όσον αφορά τον εντοπισμό και την παρακολούθηση. • Προσαρμογή σε σύνθετες κυκλοφοριακές συνθήκες όπως είναι μεταβαλλόμενες καιρικές συνθήκες (μειωμένη ορατότητα, χαμηλός φωτισμός, έντονη βροχή, χιόνι κ.λ.π.) είτε πυκνή οδική κυκλοφορία (π.χ. σε οδούς στο αστικό οδικό δίκτυο). • Γρήγορη επεξεργασία των δεδομένων εισόδου με στιβαρούς αλγόριθμους • Ελαχιστοποίηση λανθασμένων προειδοποιήσεων. • Κατασκευαστικό και λειτουργικό κόστος που θα τις καταστούν υλοποιήσιμες σε πλατιά κλίμακα. Από την ανάλυση των στοιχείων των εργασιών προκύπτει ότι υπάρχουν πολλοί τρόποι να μειωθούν σημαντικά τα σφάλματα, διατηρώντας υψηλή ακρίβεια, όπως βελτιωμένες αλγοριθμικές επιλύσεις (π.χ. με χρήση πολλαπλών εργαλείων, προχωρημένων στατιστικών και γνωστικών μεθόδων), συνδυασμός αισθητήρων (π.χ. ορατοί, IR, ραντάρ) και τηλεματική (π.χ. επικοινωνία οχήματος με όχημα, εντοπισμός με μέθοδο GPS). Σε σχέση με το λογισμικό, ένα απαραίτητο βήμα είναι η δημιουργία σταθερών προϋποθέσεων έτσι ώστε τα οπτικά συστήματα εντοπισμού οχήματος να είναι τυποποιήσιμα, επαναδιαμορφούμενα και επεκτάσιμα έτσι ώστε να μπορούν να συνεργαστούν με τη μεγάλη ποικιλία εφαρμογών επεξεργασίας. Πολύ εύστοχη θα ήταν η δημιουργία και ανάπτυξη λογισμικού που θα μπορεί να σχετίζεται με διάφορα επίπεδα αφαίρεσης συμπεριλαμβάνοντας συνδυασμό αισθητήρων, ενοποίηση ποικίλων αλγορίθμων, οικονομική χρήση πόρων, ταξινόμηση και υπολογισμούς. Επίσης η βελτίωση των ταχυτήτων των PCs έχει οδηγήσει σε αρκετά ικανοποιητικά αποτελέσματα όσον αφορά τον χρόνο επεξεργασίας, δεδομένου ότι τα συστήματα εντοπισμού κινουμένου οχήματος έχουν μεγάλες υπολογιστικές απαιτήσεις καθώς χρειάζεται να επεξεργαστούν τις ανακτώμενες εικόνες σε πραγματικό χρόνο ή κοντά σε πραγματικό χρόνο για να εξοικονομήσουν χρόνο στην αντίδραση του οδηγού. Τέλος θα πρέπει να αντικειμενικοποιηθούν οι διαδικασίες αξιολόγησης των παρουσιαζομένων μεθόδων έτσι ώστε να είναι πλέον συγκρίσιμες και ευρύτερα αποδεκτές. / -

This dissertation presents a comparative study about the performance of silicon (Si) and gallium nitride (GaN) semiconductors in drivers for light emitting diodes. Hereby, it is expected to provide the theoretical background required for the development of future works using this new technology. Theoretical aspects related to the materials used in the manufacture of semiconductors and their implications in the final product, as well as the characteristics and peculiarities of GaN semiconductors are presented. The experimental development consisted of two case studies, each focused on a distinct topology with different types of GaN semiconductors. First, a comparison of Si and enhancement mode GaN transistors was carried out in a family of synchronous buck converters. Ten 48 V to 28.3 V and 22.6 W converters were designed with the same parameters, at five different switching frequencies, ranging from 100 kHz to 1 MHz. Efficiency and temperatures were measured in four different scenarios: with and without an external diode in parallel with the low-side switch and with two different dead-time values, 25 ns and 50 ns. Converters with GaN transistors showed higher efficiency and lower temperatures in all cases, with a maximum efficiency of 96.8% and a minimum of 94.5%. In addition, Si-based converters exhibited greater performance degradation as the switching frequency and dead time increased. In the second study, nine 75 W off-line integrated double buck-boost converters were developed and evaluated. Two different Si technologies were compared with a cascode GaN transistor at three switching frequencies, ranging from 50 to 150 kHz. Again, the efficiency and temperatures of the prototypes were measured. The converters with GaN demonstrated superior performance in all cases, yielding about 5% gain in efficiency over the worst tested Si semiconductor. In both cases, the converters’ loss distribution was presented based on simulation results. It was concluded that the gallium nitride transistors have the potential to replace silicon technology mainly due to its superior performance and requirement of small, or no change, in the original circuit. / A presente dissertação apresenta um estudo comparativo do desempenho de semicondutores de silício (Si) e nitreto de gálio (GaN) em circuitos utilizados na alimentação de diodos emissores de luz. Por meio deste, procura-se fornecer o embasamento teórico necessário para o desenvolvimento de trabalhos futuros utilizando esta nova tecnologia. São apresentados, inicialmente, aspectos teóricos relacionados aos materiais utilizados na fabricação de semicondutores e suas implicações no produto final, além das características e peculiaridades dos semicondutores GaN. O desenvolvimento experimental consistiu de dois estudos de caso, cada um focado em uma topologia distinta com tipos de semicondutores GaN diferentes. Primeiramente, realizou-se um comparativo de transistores Si e GaN do tipo intensificação em uma família de conversores buck síncronos. Dez conversores 48 V para 28,3 V e 22,6 W foram projetados, com os mesmos parâmetros, em cinco diferentes frequências de comutação, variando de 100 kHz a 1 MHz. Eficiência e temperaturas foram medidas em quatro diferentes cenários: com e sem um diodo externo em paralelo com o interruptor de roda-livre e com dois valores diferentes de tempo morto, 25 ns e 50 ns. Os conversores com transistores GaN apresentaram maior eficiência e menores temperaturas em todos os casos, com uma eficiência máxima de 96,8% e uma mínima de 94,5%. Além disso, os conversores com Si exibiram uma maior degradação de desempenho à medida que a frequência de comutação e o tempo morto aumentam. No segundo estudo, nove conversores duplo buck-boost integrados de 75 W com alimentação a partir da rede elétrica foram desenvolvidos e avaliados. Compararam-se duas tecnologias distintas de interruptores de Si com um transistor GaN do tipo cascode, em três frequências de comutação, variando de 50 a 150 kHz. Novamente, mediu-se a eficiência e temperaturas dos protótipos. Os conversores com GaN demonstraram desempenho superior em todos os casos, com um ganho de cerca de 5% no rendimento em relação ao pior semicondutor Si testado. Em ambos os estudos de caso, a distribuição de perdas dos conversores foi apresentada com base em resultados de simulação. Concluiu-se que os transistores de nitreto de gálio têm potencial para substituir a tecnologia de silício utilizada atualmente devido, principalmente, a seu desempenho superior e exigência de pouca, ou nenhuma, mudança no circuito original.