This paper describes a process for dynamically controlling toll fees on HOT (High Occupancy Toll)... more This paper describes a process for dynamically controlling toll fees on HOT (High Occupancy Toll) lanes. The main control variable is the traffic volume at the entrance of the HOT lane; the reference variable is a user defined traffic volume. The toll fee is set on the basis of estimated demand and willingness to pay (predictive component). A feedback component is used to automatically correct the toll fee based on real time detector readings. The overall framework includes mechanisms to react to a deterioration of the traffic state inside the HOT lane by adjusting the control variable. Tests with microscopic traffic flow simulation show that the toll fee calculation mechanism functions as intended.
Bicyclists are amongst the most flexible road users and can tactically choose their pathway acros... more Bicyclists are amongst the most flexible road users and can tactically choose their pathway across an intersection using available bicycle lanes, roadways and sidewalks, riding either with or against the direction of travel. This flexibility makes it difficult to accurately include the pathfinding behaviour of bicyclists in microscopic traffic simulation tools due to the limitations imposed by the internal design structure of the network elements. In this paper, a method for simulating the pathfinding behaviour of bicyclists crossing an intersection based on observed trajectory data is integrated with SUMO. This is done using a SUMO extension that enables exact road user placement in the simulation. The position coordinates [x,y] of externally simulated bicycles are translated within SUMO and the bicyclist is inserted at the given location on a lane of one of the edges or junctions in each simulation step. This approach for model integration in SUMO is evaluated and recommendations for future research are given.
This article describes MOTION, a traffic signal control system, which consists of a network and a... more This article describes MOTION, a traffic signal control system, which consists of a network and a local level and builds on enhanced dynamic traffic state estimation. Special consideration is given to the modularity of the system, its flexibility to cope with different practical situations, and to the prioritization of public transit.
Electrifying mobility-on-demand (MoD) fleets is an important step towards a more sustainable tran... more Electrifying mobility-on-demand (MoD) fleets is an important step towards a more sustainable transportation system. With increasing fleet size, MoD operators will be able to participate in the energy exchange market and will have access to time-varying electricity prices. They can benefit from intelligent scheduling of charging processes considering forecasts of electricity prices and vehicle utilization. Considering a long time horizon of, e.g., a day improves scheduling decisions, but electricity prices change in a short interval of 15 minutes; hence, an optimization-based approach needs to overcome challenges regarding computational time. For this reason, we develop a macroscopic model to study the tradeoffs between electricity, battery wear and level-of-service costs. In scenarios with varying fleet size and different numbers of charging units, we compare the performance of several reactive and scheduling policies in a simulation framework based on a macroscopic model. Overall, the results of the study show that an MoD provider with 2000 vehicles could save several thousands of euros in daily operational costs by changing from a state of charge reactive charging strategy to one adapting to the price fluctuations of the electricity exchange market.
The degradation of road network performance due to incidents is a major concern to traffic operat... more The degradation of road network performance due to incidents is a major concern to traffic operators. The development of urban traffic incident management systems requires a comprehensive understanding of traffic dynamics during incidents. Recently, the concept of the macroscopic fundamental diagram (MFD) contributed to such an understanding and has been used in a wide range of applications. However, the MFD is merely reproducible under recurring traffic patterns. Motivated by a few studies which argue the existence of the MFD with a clockwise hysteresis loop during incidents, we tackle this limitation of the MFD and propose a framework to study the characteristics of the MFD under non-recurring congestion. More specifically, we introduce a criticality score (CS) which represents network redundancy and postulate that links with a higher level of CS impose a larger hysteresis loop on the MFD. We design an experiment in a microscopic traffic simulation to study the relation of closed links and the resulting MFDs. The results confirm our postulation and we observe that links with similar CS have a comparable impact on the shape of the MFD. The main contribution of this paper is the possibility to develop a framework for incident detection in urban networks under limited sensor coverage. However, the findings of the study may strongly rely on the assumptions, for instance, the network structure, the OD pairs, and drivers route choice during incidents. Thus, future studies are required to study other network topologies as well as more realistic driver route choice during incidents.
Alle Rechte, auch das des auszugsweisen Nachdruckes, der auszugsweisen oder vollständigen Wiederg... more Alle Rechte, auch das des auszugsweisen Nachdruckes, der auszugsweisen oder vollständigen Wiedergabe, der Speicherung in Datenverarbeitungsanlagen und der Übersetzung, vorbehalten. Kurzfassung Die zunehmende Vielfalt von Datenquellen und-arten zur Beschreibung der Verkehrssituation erschwert zusehends die Integration sämtlicher verfügbarer Informationen in bestehende Verfahren zur Verkehrslageschätzung. Dadurch können diese Verfahren entscheidende Nachteile hinsichtlich der Qualität ihrer Schätzergebnisse erleiden. Die vorliegende Arbeit beschreibt eine neue Methode, die die Berücksichtigung aller Datenarten erlaubt und für alle eingehenden, auch gering verfügbaren Kenngrößen kontinuierlich Schätzwerte liefern kann. Sie verfolgt einen statistischen Ansatz und setzt folglich kein Verkehrsflussmodell ein. Durch abschnittsweise lineare Regressionsanalyse werden aus historischen Daten Näherungsfunktionen zur Schätzung von Verkehrskenngrößen aus anderen Kenngrößen ermittelt, sofern die Erhebungsorte von Ein-und Ausgangskenngröße ein Kriterium der räumlichen Nähe erfüllen. Dieser Ansatz erlaubt die Beschreibung auch von Zusammenhängen, die nicht über den gesamten Wertebereich linear sind, sowie die nach Wertebereichen differenzierte qualitative Beurteilung der Zusammenhänge. Bei der Zusammenführung zahlreicher Schätzwerte für eine Kenngröße werden die Einzelschätzungen aus den stärksten Zusammenhängen verwendet. Die zusammengeführten Schätzwerte vervollständigen den aktuellen Datenbestand und dienen der Plausibilisierung von Messwerten. Gehen fahrzeuggenerierte Daten in das Verfahren ein, kann die Verkehrslage netzweit und linkfein geschätzt werden. Das neue Verfahren wird erprobt mit lokalen Daten, mit Abschnittsdaten aus infrastrukturseitiger Fahrzeugwiedererkennung sowie mit Linkgeschwindigkeiten aus Positionsmeldungen einer Taxiflotte. Als Historie werden Daten verwendet, die im Laufe von drei Monaten in einem Netzausschnitt im Münchner Norden gesammelt wurden. Die Ergebnisse der Regressionsanalyse werden differenziert nach Datenart von Ein-und Ausgangsgröße, nach Verkehrszustand sowie nach zeitlichem Versatz zwischen Ein-und Ausgangsgröße für verschiedene Varianten der Regressionsanalyse untersucht. Diese Varianten beleuchten neben der einfachen die gewichtete lineare Regression sowie die nach Tagestyp und-zeit differenzierte Auswertung. Im Allgemeinen bestätigen sich Erwartungen, die auf der Kenntnis des Fundamentaldiagramms und auf statistischen Vorüberlegungen basieren. Lokale Belegungsgrade und Routenreisezeiten erweisen sich als besonders aussagekräftige Eingangsgrößen. Zur Bewertung zusammengeführter Schätzergebnisse werden ein geeignetes Fehlermaß und die Detektionsrate von Perzentilereignissen verwendet, angewandt auf einen Zeitraum von einer Woche. Varianten des entwickelten Ansatzes werden mit einem Ganglinienverfahren, mit der Trivialprognose und mit einer pragmatischen Kombination aus beiden verglichen. Für das neue Verfahren werden bei der Schätzung infrastrukturseitig erhobener Daten fast durchgängig die besten Kennwerte ermittelt. Messwerte dienen hierbei als Referenz. Für geschätzte Linkreisezeiten fehlt eine solche Referenz. Verschiedene Untersuchungsansätze zeigen aber, dass qualitativ und quantitativ plausible Schätzergebnisse erzielt werden.
The 21st century is characterized not only by a growing need for mobility, but above all by an in... more The 21st century is characterized not only by a growing need for mobility, but above all by an increasing variety of mobility forms. Individualization, connectivity, urbanization and post-fossil drive technologies will determine the mobility of tomorrow. Technical innovations and changing human needs are becoming the driving force behind novel forms of mobility and innovative business models. However, not only the mobility world is changing rapidly. Particularly renewable energy sources, like sun and wind are directly connected to planning uncertainty due to their dependence on weather. This leads to frequency fluctuations in the power grid. These fluctuations in turn are the reason for dynamic electricity prices to which especially large consumers can adapt in order to save money. This paper investigates to what extent an operating electric mobility on-demand fleet can adjust to changing electricity prices and whether this adaptation affects the service performance of the overall system. For this purpose, a model is built up, which considers traffic influences in the form of dynamic travel times as well as the passenger and battery management of the vehicles. The model suggests that a vehicle fleet with an adapted charging strategy to dynamic electricity prices can save money at all investigated fleet sizes. First results indicate that the service performance of the mobility on-demand fleet is not substantially affected. In addition, considerable cost savings can be realized by applying the dynamic charging strategy. The analysis of idle times of the vehicle fleet revealed further potential for optimization, which could potentially be used for the provision of ancillary services.
IEEE Transactions on Intelligent Transportation Systems, Apr 1, 2020
Current Urban Traffic Control (UTC) systems rely heavily on inductive loop detectors. The emergen... more Current Urban Traffic Control (UTC) systems rely heavily on inductive loop detectors. The emergence of Connected Vehicles (CV) opens new possibilities for improving signal control, while reducing the need for loop detectors. However, for low penetration rates, the CV measurements are sporadic and thus difficult to exploit by existing UTC systems. In this paper, a methodology that enables cycle-to-cycle traffic state estimation and prediction based on limited CV measurements is presented. Furthermore, the proposed formulation enables fusion of CV with other data sources and their integration in any UTC system. The developed Extended Observer (EO) is a discrete-time, variabledimension implementation of the Extended Kalman Filter. It does not require loop detectors and is independent of the type of signal control. The evaluation focuses on the queue length estimation. Especially in oversaturation, the EO outperforms the CV measurements for all examined penetration rates. Moreover, the highest benefit is observed for the lowest penetration rates. The results show that for oversaturation and low penetration rates the EO improves the CV measurements 13-31%. In addition, the EO is tested with an adaptive UTC system by feeding the fused estimation from CV and camera measurements. The error in queue length estimation from the EO is significantly lower than the error based on stochastic arrivals. Additionally, the results show a reduction in delays at the examined signal and the complete intersection. Overall, this paper sheds light on the potential benefits from enhancing limited CV measurements in order to contribute immediately to current UTC systems.
Higher levels of market penetration of dynamic route guidance systems, such as the EURO-SCOUT sys... more Higher levels of market penetration of dynamic route guidance systems, such as the EURO-SCOUT system from Siemens, require that some form of adjustment is made for the consequences of routeing recommendations. Ideally a procedure is required that generates route recommendations such that no guided driver could have taken a faster route. This is a form of Wardrop equilibrium, and necessitates a dynamic equilibrium assignment algorithm in order to obtain such a set of route recommendations. The determination of a dynamic equilibrium assignment requires the derivation of travel time functions. In this paper it is proposed that link travel time measurements from the dynamic route guidance system be combined with link flow measurements from a traffic signal control system, and that the coefficients of the link travel time functions be estimated recursively. A modified Frank-Wolfe algorithm. for solving the dynamic equilibrium assignment problem is proposed. This requires the iterative use of a shortest path algorithm, such as that currently implemented in the EURO-SCOUT system. The properties of the algorithm are explored using a small numerical example.
Transportation Research Part B-methodological, Aug 1, 2021
The well-known Lighthill-Whitham-Richards (LWR) theory is the fundamental pillar for most macrosc... more The well-known Lighthill-Whitham-Richards (LWR) theory is the fundamental pillar for most macroscopic traffic models. In the past, many methods were developed to numerically derive solutions for LWR problems. Examples for such numerical solution schemes are the cell transmission model, the link transmission model, and the variational theory (VT) of traffic flow. So far, the latter framework found applications in the fields of traffic modelling, macroscopic fundamental diagram estimation, multi-modal traffic analyses, and data fusion. However, these studies apply VT only at the link or corridor level. To the best of our knowledge, there is no methodology yet to apply VT at the network level. We address this gap by developing a VT-based framework applicable to networks. Our model allows us to account for source terms (e.g. inflows and outflows at intersections) and the propagation of spillbacks between adjacent corridors consistent with kinematic wave theory. We show that the trajectories extracted from a microscopic simulation fit the predicted traffic states from our model for a simple intersection with both source terms and spillbacks. We also use this simple example to illustrate the accuracy of the proposed model. Additionally, we apply our model to the Sioux Falls network and again compare the results to those from a microscopic simulation. Our results indicate a close fit of traffic states, but with substantially
Replacement of conventional taxis by automated vehicles will challenge taxi operation in many way... more Replacement of conventional taxis by automated vehicles will challenge taxi operation in many ways. Decisions made by taxi drivers will be substituted by an integrated scheduling system that also manages the non-revenue generating activities such as vehicle pre-allocation, recharging and service trips. In order to tackle this challenge, this study introduces a theoretical framework for autonomous vehicles based on the model of a family. The family model decomposes the complexity of scheduling for automated vehicle fleets. It allows vehicles to negotiate among them in a decentralized fashion and at the same time it allows the fleet manager to set fleet priorities and to pre-allocate vehicles in locations of expected future demand. Furthermore, it proposes a transparent framework for communication with service providers. Moreover, this study discusses selected opportunities and challenges of automated vehicle fleets.
This paper describes a process for dynamically controlling toll fees on HOT (High Occupancy Toll)... more This paper describes a process for dynamically controlling toll fees on HOT (High Occupancy Toll) lanes. The main control variable is the traffic volume at the entrance of the HOT lane; the reference variable is a user defined traffic volume. The toll fee is set on the basis of estimated demand and willingness to pay (predictive component). A feedback component is used to automatically correct the toll fee based on real time detector readings. The overall framework includes mechanisms to react to a deterioration of the traffic state inside the HOT lane by adjusting the control variable. Tests with microscopic traffic flow simulation show that the toll fee calculation mechanism functions as intended.
Bicyclists are amongst the most flexible road users and can tactically choose their pathway acros... more Bicyclists are amongst the most flexible road users and can tactically choose their pathway across an intersection using available bicycle lanes, roadways and sidewalks, riding either with or against the direction of travel. This flexibility makes it difficult to accurately include the pathfinding behaviour of bicyclists in microscopic traffic simulation tools due to the limitations imposed by the internal design structure of the network elements. In this paper, a method for simulating the pathfinding behaviour of bicyclists crossing an intersection based on observed trajectory data is integrated with SUMO. This is done using a SUMO extension that enables exact road user placement in the simulation. The position coordinates [x,y] of externally simulated bicycles are translated within SUMO and the bicyclist is inserted at the given location on a lane of one of the edges or junctions in each simulation step. This approach for model integration in SUMO is evaluated and recommendations for future research are given.
This article describes MOTION, a traffic signal control system, which consists of a network and a... more This article describes MOTION, a traffic signal control system, which consists of a network and a local level and builds on enhanced dynamic traffic state estimation. Special consideration is given to the modularity of the system, its flexibility to cope with different practical situations, and to the prioritization of public transit.
Electrifying mobility-on-demand (MoD) fleets is an important step towards a more sustainable tran... more Electrifying mobility-on-demand (MoD) fleets is an important step towards a more sustainable transportation system. With increasing fleet size, MoD operators will be able to participate in the energy exchange market and will have access to time-varying electricity prices. They can benefit from intelligent scheduling of charging processes considering forecasts of electricity prices and vehicle utilization. Considering a long time horizon of, e.g., a day improves scheduling decisions, but electricity prices change in a short interval of 15 minutes; hence, an optimization-based approach needs to overcome challenges regarding computational time. For this reason, we develop a macroscopic model to study the tradeoffs between electricity, battery wear and level-of-service costs. In scenarios with varying fleet size and different numbers of charging units, we compare the performance of several reactive and scheduling policies in a simulation framework based on a macroscopic model. Overall, the results of the study show that an MoD provider with 2000 vehicles could save several thousands of euros in daily operational costs by changing from a state of charge reactive charging strategy to one adapting to the price fluctuations of the electricity exchange market.
The degradation of road network performance due to incidents is a major concern to traffic operat... more The degradation of road network performance due to incidents is a major concern to traffic operators. The development of urban traffic incident management systems requires a comprehensive understanding of traffic dynamics during incidents. Recently, the concept of the macroscopic fundamental diagram (MFD) contributed to such an understanding and has been used in a wide range of applications. However, the MFD is merely reproducible under recurring traffic patterns. Motivated by a few studies which argue the existence of the MFD with a clockwise hysteresis loop during incidents, we tackle this limitation of the MFD and propose a framework to study the characteristics of the MFD under non-recurring congestion. More specifically, we introduce a criticality score (CS) which represents network redundancy and postulate that links with a higher level of CS impose a larger hysteresis loop on the MFD. We design an experiment in a microscopic traffic simulation to study the relation of closed links and the resulting MFDs. The results confirm our postulation and we observe that links with similar CS have a comparable impact on the shape of the MFD. The main contribution of this paper is the possibility to develop a framework for incident detection in urban networks under limited sensor coverage. However, the findings of the study may strongly rely on the assumptions, for instance, the network structure, the OD pairs, and drivers route choice during incidents. Thus, future studies are required to study other network topologies as well as more realistic driver route choice during incidents.
Alle Rechte, auch das des auszugsweisen Nachdruckes, der auszugsweisen oder vollständigen Wiederg... more Alle Rechte, auch das des auszugsweisen Nachdruckes, der auszugsweisen oder vollständigen Wiedergabe, der Speicherung in Datenverarbeitungsanlagen und der Übersetzung, vorbehalten. Kurzfassung Die zunehmende Vielfalt von Datenquellen und-arten zur Beschreibung der Verkehrssituation erschwert zusehends die Integration sämtlicher verfügbarer Informationen in bestehende Verfahren zur Verkehrslageschätzung. Dadurch können diese Verfahren entscheidende Nachteile hinsichtlich der Qualität ihrer Schätzergebnisse erleiden. Die vorliegende Arbeit beschreibt eine neue Methode, die die Berücksichtigung aller Datenarten erlaubt und für alle eingehenden, auch gering verfügbaren Kenngrößen kontinuierlich Schätzwerte liefern kann. Sie verfolgt einen statistischen Ansatz und setzt folglich kein Verkehrsflussmodell ein. Durch abschnittsweise lineare Regressionsanalyse werden aus historischen Daten Näherungsfunktionen zur Schätzung von Verkehrskenngrößen aus anderen Kenngrößen ermittelt, sofern die Erhebungsorte von Ein-und Ausgangskenngröße ein Kriterium der räumlichen Nähe erfüllen. Dieser Ansatz erlaubt die Beschreibung auch von Zusammenhängen, die nicht über den gesamten Wertebereich linear sind, sowie die nach Wertebereichen differenzierte qualitative Beurteilung der Zusammenhänge. Bei der Zusammenführung zahlreicher Schätzwerte für eine Kenngröße werden die Einzelschätzungen aus den stärksten Zusammenhängen verwendet. Die zusammengeführten Schätzwerte vervollständigen den aktuellen Datenbestand und dienen der Plausibilisierung von Messwerten. Gehen fahrzeuggenerierte Daten in das Verfahren ein, kann die Verkehrslage netzweit und linkfein geschätzt werden. Das neue Verfahren wird erprobt mit lokalen Daten, mit Abschnittsdaten aus infrastrukturseitiger Fahrzeugwiedererkennung sowie mit Linkgeschwindigkeiten aus Positionsmeldungen einer Taxiflotte. Als Historie werden Daten verwendet, die im Laufe von drei Monaten in einem Netzausschnitt im Münchner Norden gesammelt wurden. Die Ergebnisse der Regressionsanalyse werden differenziert nach Datenart von Ein-und Ausgangsgröße, nach Verkehrszustand sowie nach zeitlichem Versatz zwischen Ein-und Ausgangsgröße für verschiedene Varianten der Regressionsanalyse untersucht. Diese Varianten beleuchten neben der einfachen die gewichtete lineare Regression sowie die nach Tagestyp und-zeit differenzierte Auswertung. Im Allgemeinen bestätigen sich Erwartungen, die auf der Kenntnis des Fundamentaldiagramms und auf statistischen Vorüberlegungen basieren. Lokale Belegungsgrade und Routenreisezeiten erweisen sich als besonders aussagekräftige Eingangsgrößen. Zur Bewertung zusammengeführter Schätzergebnisse werden ein geeignetes Fehlermaß und die Detektionsrate von Perzentilereignissen verwendet, angewandt auf einen Zeitraum von einer Woche. Varianten des entwickelten Ansatzes werden mit einem Ganglinienverfahren, mit der Trivialprognose und mit einer pragmatischen Kombination aus beiden verglichen. Für das neue Verfahren werden bei der Schätzung infrastrukturseitig erhobener Daten fast durchgängig die besten Kennwerte ermittelt. Messwerte dienen hierbei als Referenz. Für geschätzte Linkreisezeiten fehlt eine solche Referenz. Verschiedene Untersuchungsansätze zeigen aber, dass qualitativ und quantitativ plausible Schätzergebnisse erzielt werden.
The 21st century is characterized not only by a growing need for mobility, but above all by an in... more The 21st century is characterized not only by a growing need for mobility, but above all by an increasing variety of mobility forms. Individualization, connectivity, urbanization and post-fossil drive technologies will determine the mobility of tomorrow. Technical innovations and changing human needs are becoming the driving force behind novel forms of mobility and innovative business models. However, not only the mobility world is changing rapidly. Particularly renewable energy sources, like sun and wind are directly connected to planning uncertainty due to their dependence on weather. This leads to frequency fluctuations in the power grid. These fluctuations in turn are the reason for dynamic electricity prices to which especially large consumers can adapt in order to save money. This paper investigates to what extent an operating electric mobility on-demand fleet can adjust to changing electricity prices and whether this adaptation affects the service performance of the overall system. For this purpose, a model is built up, which considers traffic influences in the form of dynamic travel times as well as the passenger and battery management of the vehicles. The model suggests that a vehicle fleet with an adapted charging strategy to dynamic electricity prices can save money at all investigated fleet sizes. First results indicate that the service performance of the mobility on-demand fleet is not substantially affected. In addition, considerable cost savings can be realized by applying the dynamic charging strategy. The analysis of idle times of the vehicle fleet revealed further potential for optimization, which could potentially be used for the provision of ancillary services.
IEEE Transactions on Intelligent Transportation Systems, Apr 1, 2020
Current Urban Traffic Control (UTC) systems rely heavily on inductive loop detectors. The emergen... more Current Urban Traffic Control (UTC) systems rely heavily on inductive loop detectors. The emergence of Connected Vehicles (CV) opens new possibilities for improving signal control, while reducing the need for loop detectors. However, for low penetration rates, the CV measurements are sporadic and thus difficult to exploit by existing UTC systems. In this paper, a methodology that enables cycle-to-cycle traffic state estimation and prediction based on limited CV measurements is presented. Furthermore, the proposed formulation enables fusion of CV with other data sources and their integration in any UTC system. The developed Extended Observer (EO) is a discrete-time, variabledimension implementation of the Extended Kalman Filter. It does not require loop detectors and is independent of the type of signal control. The evaluation focuses on the queue length estimation. Especially in oversaturation, the EO outperforms the CV measurements for all examined penetration rates. Moreover, the highest benefit is observed for the lowest penetration rates. The results show that for oversaturation and low penetration rates the EO improves the CV measurements 13-31%. In addition, the EO is tested with an adaptive UTC system by feeding the fused estimation from CV and camera measurements. The error in queue length estimation from the EO is significantly lower than the error based on stochastic arrivals. Additionally, the results show a reduction in delays at the examined signal and the complete intersection. Overall, this paper sheds light on the potential benefits from enhancing limited CV measurements in order to contribute immediately to current UTC systems.
Higher levels of market penetration of dynamic route guidance systems, such as the EURO-SCOUT sys... more Higher levels of market penetration of dynamic route guidance systems, such as the EURO-SCOUT system from Siemens, require that some form of adjustment is made for the consequences of routeing recommendations. Ideally a procedure is required that generates route recommendations such that no guided driver could have taken a faster route. This is a form of Wardrop equilibrium, and necessitates a dynamic equilibrium assignment algorithm in order to obtain such a set of route recommendations. The determination of a dynamic equilibrium assignment requires the derivation of travel time functions. In this paper it is proposed that link travel time measurements from the dynamic route guidance system be combined with link flow measurements from a traffic signal control system, and that the coefficients of the link travel time functions be estimated recursively. A modified Frank-Wolfe algorithm. for solving the dynamic equilibrium assignment problem is proposed. This requires the iterative use of a shortest path algorithm, such as that currently implemented in the EURO-SCOUT system. The properties of the algorithm are explored using a small numerical example.
Transportation Research Part B-methodological, Aug 1, 2021
The well-known Lighthill-Whitham-Richards (LWR) theory is the fundamental pillar for most macrosc... more The well-known Lighthill-Whitham-Richards (LWR) theory is the fundamental pillar for most macroscopic traffic models. In the past, many methods were developed to numerically derive solutions for LWR problems. Examples for such numerical solution schemes are the cell transmission model, the link transmission model, and the variational theory (VT) of traffic flow. So far, the latter framework found applications in the fields of traffic modelling, macroscopic fundamental diagram estimation, multi-modal traffic analyses, and data fusion. However, these studies apply VT only at the link or corridor level. To the best of our knowledge, there is no methodology yet to apply VT at the network level. We address this gap by developing a VT-based framework applicable to networks. Our model allows us to account for source terms (e.g. inflows and outflows at intersections) and the propagation of spillbacks between adjacent corridors consistent with kinematic wave theory. We show that the trajectories extracted from a microscopic simulation fit the predicted traffic states from our model for a simple intersection with both source terms and spillbacks. We also use this simple example to illustrate the accuracy of the proposed model. Additionally, we apply our model to the Sioux Falls network and again compare the results to those from a microscopic simulation. Our results indicate a close fit of traffic states, but with substantially
Replacement of conventional taxis by automated vehicles will challenge taxi operation in many way... more Replacement of conventional taxis by automated vehicles will challenge taxi operation in many ways. Decisions made by taxi drivers will be substituted by an integrated scheduling system that also manages the non-revenue generating activities such as vehicle pre-allocation, recharging and service trips. In order to tackle this challenge, this study introduces a theoretical framework for autonomous vehicles based on the model of a family. The family model decomposes the complexity of scheduling for automated vehicle fleets. It allows vehicles to negotiate among them in a decentralized fashion and at the same time it allows the fleet manager to set fleet priorities and to pre-allocate vehicles in locations of expected future demand. Furthermore, it proposes a transparent framework for communication with service providers. Moreover, this study discusses selected opportunities and challenges of automated vehicle fleets.
The interest in automated vehicles (AVs) and their potential impact on the safety and efficiency ... more The interest in automated vehicles (AVs) and their potential impact on the safety and efficiency of traffic is increasing more and more every day. Accident analyses have shown, that most of the current accidents are related to human misbehavior. AVs are promised to be able to avoid some of the driver’s failures like driver inattention and to harmonize the traffic flow. However, investigating implications of higher levels of automation has been somewhat constrained by the fact that the development and implementation of this technology is still an ongoing process. On the other hand, these vehicles are not yet widespread present in current car traffic flow. Therefore, the safety measures such as accidents and fatality frequencies cannot be obtained. Hence, this study seeks to investigate the potential effects of AVs on freeways in terms of operational and safety performance using microscopic traffic simulation. It is largely argued that these vehicles cannot have a driving behavior which is considerably different from human driving behavior as long as they are operating in mixed traffic. Therefore, the simulated AVs in this study follow the current recommendations of the German Road Traffic Act (StVO) and they can only have a more aggressive driving behavior when having another AV as predecessor. Moreover, this study investigates the potential effects of different penetration rates of AVs on safety using various surrogate safety indicators such as time to collision (TTC), time integrated time to collision (TIT), time exposed to collision (TET), and modified deceleration rate to avoid collision (MDRAC).
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Papers by Fritz Busch