| 1. |
- Karlsson, Johan, 1991, et al.
(författare)
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Intersection crossing with reduced number of conflicts
- 2018
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Ingår i: IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC. ; , s. 1993-1999
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Konferensbidrag (refereegranskat)abstract
- In this paper, an optimization based algorithm for safe and efficient collaborative driving in intersections is formulated. The problem is to determine the optimal order in which vehicles should travel through an intersection under the assumptions that the longitudinal velocity of all vehicles can be controlled along a predefined path. In the original formulation one quadratic optimization program was solved for each possible crossing order of the vehicles and collisions were avoided by formulating constraints that only allowed one vehicle at the time inside the intersection. To make this algorithm more effective, we formulate less restrictive collision avoidance constraints by introducing one critical zone for each point where two predefined paths cross. It is shown that this formulation leads to a decrease in the number of quadratic optimization programs that need to be solved to find the best crossing order. Further, an algorithm is provided that finds the number of crossing sequences which yield unique formulations of the optimization program. The results show that when simulating more complex scenarios, like four vehicles traveling through an ordinary intersection, the reduction of computational time and the total time it takes for all vehicles to make it through the intersection can be significantly reduced using these less restrictive constraints.
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| 2. |
- Dozza, Marco, 1978, et al.
(författare)
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A data-driven framework for the safe integration of micro-mobility into the transport system: Comparing bicycles and e-scooters in field trials
- 2022
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Ingår i: Journal of Safety Research. - : Elsevier BV. - 0022-4375. ; 81, s. 67-77
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Tidskriftsartikel (refereegranskat)abstract
- Introduction : Recent advances in technology create new opportunities for micro-mobility solutions even as they pose new challenges to transport safety. For instance, in the last few years, e-scooters have become increasingly popular in several cities worldwide; however, in many cases, the municipalities were simply unprepared for the new competition for urban space between traditional road users and e-scooters, so that bans became a necessary, albeit drastic, solution. In many countries, traditional vehicles (such as bicycles) may not be intrinsically safer than e-scooters but are considered less of a safety threat, possibly because—for cyclists—social norms, traffic regulations, and access to infrastructure are established, reducing the number of negative stakeholders. Understanding e-scooter kinematics and e-scooterist behavior may help resolve conflicts among road users, by favoring a data-driven integration of these new e-vehicles into the transport system. In fact, regulations and solutions supported by data are more likely to be acceptable and effective for all stakeholders. As new personal-mobility solutions enter the market, e-scooters may just be the beginning of a micro-mobility revolution. Method : This paper introduces a framework (including planning, execution, analysis, and modeling) for a data-driven evaluation of micro-mobility vehicles. The framework leverages our experience assessing bicycle dynamics in real traffic to make objective and subjective comparisons across different micro-mobility solutions. In this paper, we use the framework to compare bicycles and e-scooters in field tests. Results : The preliminary results show that e-scooters may be more maneuverable and comfortable than bicycles, although the former require longer braking distances. Practical Applications : Data collected from e-scooters may, in the short term, facilitate policy making, geo-fencing solutions, and education; in the long run, the same data will promote the integration of e-scooters into a cooperative transport system in which connected automated vehicles share the urban space with micro-mobility vehicles. Finally, the framework and the models presented in this paper may serve as a reference for the future assessment of new micro-mobility vehicles and their users’ behavior (although advances in technology and novel micro-mobility solutions will inevitably require some adjustments).
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| 3. |
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| 4. |
- Dozza, Marco, 1978, et al.
(författare)
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How do different micro-mobility vehicles affect longitudinal control? Results from a field experiment
- 2023
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Ingår i: Journal of Safety Research. - : Elsevier BV. - 0022-4375. ; 84, s. 24-32
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Tidskriftsartikel (refereegranskat)abstract
- Introduction : While micromobility vehicles offer new transport opportunities and may decrease fuel emissions, the extent to which these benefits outweigh the safety costs is still uncertain. For instance, e-scooterists have been reported to experience a tenfold crash risk compared to ordinary cyclists. Today, we still do not know whether the real safety problem is the vehicle, the human, or the infrastructure. In other words, the new vehicles may not necessarily be unsafe; the behavior of their riders, in combination with an infrastructure that was not designed to accommodate micromobility, may be the real issue. Method : In this paper, we compared e-scooters and Segways with bicycles in field trials to determine whether these new vehicles create different constraints for longitudinal control (e.g., in braking avoidance maneuvers). Results : The results show that acceleration and deceleration performance changes across vehicles; specifically, e-scooters and Segways that we tested cannot brake as efficiently as bicycles. Further, bicycles are experienced as more stable, maneuverable, and safe than Segways and e-scooters. We also derived kinematic models for acceleration and braking that can be used to predict rider trajectories in active safety systems. Practical Applications : The results from this study suggest that, while new micromobility solutions may not be intrinsically unsafe, they may require some behavior and/or infrastructure adaptations to improve their safety. We also discuss how policy making, safety system design, and traffic education may use our results to support the safe integration of micromobility into the transport system.
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| 5. |
- Dozza, Marco, 1978, et al.
(författare)
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Modelling Interaction between Cyclists and Automobiles - Final Report
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The MICA project modelled driver behaviour, focusing on the approaching phase of an overtaking manoeuvre, when a driver moved toward a cyclist while facing oncoming traffic (Euro NCAP test protocols inspired this scenario.). The model predicts the probability for drivers to brake or steer as they approach the cyclists to perform an accelerative (overtake after the oncoming traffic has passed) or flying (overtake before the oncoming traffic has passed) manoeuvre, respectively. This model has been integrated into a smart collision-avoidance system, that provides early (and yet acceptable) warnings and interventions. A virtual assessment estimated the safety benefits of the smart collision-avoidance system using UDRIVE naturalistic data. Our analyses show that the new smart collision-avoidance system can significantly reduce fatalities and severe injuries when compared to traditional collision-avoidance systems, with the new collision warning alone promising a reduction of fatalities by 53-96% and a reduction of serious injuries by 43-93%. This work has been carried out by three PhD students and is now continuing in the MICA2 project. The main deliverables of the project were: 1) a unique dataset collected on the airfield in Vårgårda where participants interacted with two robots, 2) a new modelling framework that helps to identify interaction on a scenario basis, 3) a novel driver model, which can predict overtaking strategy in real-time, 4) a smart collision-avoidance system which uses the driver model to generate warnings and automated interventions, and 5) a safety benefit analysis, proving the potential for the new collision-avoidance systems to save lives and reduce injuries from naturalistic European data. Nine scientific contributions describe MICA’s results: one licentiate thesis, two podium presentations to the International Cycling Safety Conference (2018 and 2019, respectively), one conference paper submitted to the Transport Research Arena 2020, and five journal papers. MICA highlighted that: 1) Modelling the interaction between the overtaking vehicle and the oncoming vehicle is an essential step to increase overtaking safety. 2) The approaching phase of an overtaking manoeuvre is not necessarily the riskiest; the most significant margin for improving safety may lay in developing systems that support the drivers in the returning phase. 3) In the approaching phase of an overtaking manoeuvre, the potential safety benefits from automated emergency steering (a system not addressed in MICA) is substantial. 4) As an overtaking manoeuvre develops from the approaching to the steering, passing, and returning phase, vehicle kinematics and proximities become more critical, challenging active safety systems and calling for new passive safety solutions. 5) More experimental data, collected in more critical situations than what was possible in MICA, is needed to address overtaking safety properly. New methodologies, such as augmented reality and virtual reality, offer the best opportunities to collect such data without ethical concerns. 6) More naturalistic data is needed to validate our driver models and the new systems that we started developing in MICA. 7) Interaction among road users is complex and models of vulnerable road-user behaviour are also needed to make robust predictions. As we move from an overtaking scenario to a crossing scenario, this aspect will become even more crucial. MICA2, a new FFI project including Volvo Cars, Autoliv, Veoneer, Viscando, if, VTI, and Chalmers, will now address these issues.
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| 6. |
- Dozza, Marco, 1978, et al.
(författare)
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Naturalistic micromobility data: opportunities and threats
- 2024
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Micromobility data are increasingly available and promise to support not only researchers but also policymakers and authorities in best integrating micromobility into the transport system. When micromobility data are collected in the wild by road users attending to their daily routines, these data bring unprecedented insights into the behavior of micromobility road users and their interaction with other road users and infrastructure. Although GPS data is the most widely available micromobility data, electrified vehicles (e.g., e-bikes and e-scooters) often include sophisticated sensors such as inertial measurement units and cameras. New advances in technology make it possible to analyze video data with artificial eyes and leverage artificial intelligence to model and analyze vehicle dynamics and user behavior, complementing GPS with information crucial for understanding micromobility safety, efficiency, and acceptance. Within the MicroVision and e-SAFER projects, naturalistic data from e-scooter rental services have been used to investigate crash causation and model rider behavior to improve advanced driving assistance systems, support automated driving functions, and inform Euro NCAP protocols. These projects unveiled the peculiarities and prevalence of leisure riding on e-scooters and created some of the basis for sharing micromobility data and open behavioral models. If shared, the data and models from e-SAFER may serve new analyses and promote new countermeasures based on education, policymaking, and infrastructure design. However, data sharing is a double-edged sword where issues such as ethics, privacy, and security need to find a compromise with commercial interests, while the integrity of the data and analysis results must be warranted.
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| 7. |
- Köhler, Anna, 1989, et al.
(författare)
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Experimental characterization of axial fuel mixing in fluidized beds by magnetic particle tracking
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A Magnetic Particle Tracking (MPT) system is applied to a bubbling fluidized bed to study how axial mixing and segregation of fuel are influenced by the fuel density and operational conditions (fluidization velocity, bed height and pressure drop across the gas distributor). The MPT system is used to determine the vertical distribution of the tracer particle in a fluid-dynamically down-scaled cold unit resembling a 0.74×0.74 m2 fluidized bed reactor operating at 800 °C. This work uses a tracer particle of 10 mm in diameter, corresponding to a fuel particle of 44 mm. Different tracer particles are applied with solids density representing biomass, biomass char and that of the average bulk. The MPT system yields a spatial accuracy in the order of 10-3 m and a time resolution of 10-3 s. For the operational range investigated, three fuel segregation regimes can be identified from the MPT measurements: 1) A flotsam regime which occurs at low fluidization velocities and for low density tracer particles, 2) A transition regime over which an increase in fluidization velocity results in that the presence of fuel particles at the bed surface decreases rapidly, and 3) A fully developed mixing regime in which the presence of tracer particle at the bed surface and the splash zone remains constant with fluidization velocity. The transition velocities between the regimes depend on bed height and density of the tracer particle.
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| 8. |
- Köhler, Anna, 1989, et al.
(författare)
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Experimental characterization of axial fuel mixing in fluidized beds by magnetic particle tracking
- 2017
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 316:SI, s. 492-499
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Tidskriftsartikel (refereegranskat)abstract
- A magnetic particle tracking (MPT) system is applied to a bubbling fluidized bed to study how axial mixing and segregation of fuel are influenced by the fuel density and operational conditions (fluidization velocity, bed height and pressure drop across the gas distributor). The MPT system is used to determine the vertical distribution of the tracer particle in a fluid-dynamically down-scaled cold unit resembling a 0.74×0.74 m^2 fluidized bed reactor operating at 800°C. This work uses a tracer particle of 10 mm in diameter, corresponding to a fuel particle of 44 mm. Different tracer particles are applied with solids density representing biomass, biomass char and that of the average bulk. The MPT system yields a spatial accuracy in the order of 10^-3 m and a time resolution of 10^-3 s.For the operational range investigated, three fuel segregation regimes can be identified from the MPT measurements: 1) A flotsam regime which occurs at low fluidization velocities and for low density tracer particles, 2) A transition regime over which an increase in fluidization velocity results in the presence of fuel particles at the bed surface decreases rapidly, and 3) A fully developed mixing regime in which the presence of tracer particle at the bed surface and the splash zone remains constant with fluidization velocity. The transition velocities between the regimes depend on bed height and density of the tracer particle.
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| 9. |
- Lee, Oliver, et al.
(författare)
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Modelling cyclists’ comfort zones from obstacle avoidance manoeuvres
- 2020
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 144
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a framework for modelling the cyclist’s comfort zone. Unlike the driver’s comfort zone, little is known about the cyclist’s. The framework draws on existing literature in cognitive science about driver behaviour to explain experimental results from cycling field trials, and the modelling of these results. We modelled braking and steering manoeuvres from field data of cyclists’ obstacle avoidance within their comfort zone. Results show that when cyclists avoided obstacles by braking, they kept a constant deceleration; as speed increased, they started to brake earlier, farther from the obstacle, maintaining an almost constant time to collision. When cyclists avoided obstacles by steering, they maintained a constant distance from the object, independent of speed. Overall, the higher the speed, the more the steering manoeuvres were temporally delayed compared to braking manoeuvres. We discuss these results and other similarities between cyclist and driver behaviour during obstacle avoidance. Implications for the design of acceptable active safety and infrastructure design are also addressed.
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| 10. |
- Moll, Sara, et al.
(författare)
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Modelling duration of car-bicycles overtaking manoeuvres on two-lane rural roads using naturalistic data
- 2021
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- Nowadays, Spanish two-lane rural roads frequently accommodate sport cyclists. They usually ride on the shoulder or on the right edge of the lane, sharing the infrastructure with motorised vehicles. Due to the speed difference between road users, the most frequent and dangerous interaction is in overtaking manoeuvres. One key factor from a safety and traffic operation point of view is the overtaking duration. The main aim of this paper is to analyse how factors related to the road, the cyclists, and the overtaking manoeuvre influence the duration of overtaking to cyclists on two-lane rural roads. Naturalistic field data were obtained using instrumented bicycles. Seven groups of cyclists, formed by different numbers of cyclists riding in-line and two-abreast, rode along five rural roads with different geometric and traffic characteristics. A total of 1592 flying manoeuvres, in which drivers did not reduce their speed, and 192 accelerative manoeuvres were analysed. The overtaking duration, considering each overtaking strategy, was modelled using Bayesian statistics. Results showed that flying manoeuvres were more prevalent than accelerative. They were performed with higher speeds and lower lateral clearances and, therefore, presented lower overtaking durations. For both overtaking strategies, duration increased on wider roads and with a larger size of the group. The presence of an oncoming vehicle decreased the overtaking duration. However, other factors presented opposite effects on the duration depending on the overtaking strategy. The developed predictive models allow obtaining overtaking durations varying road and cyclist grouping characteristics. Results can be used by road administration to manage and propose some specific countermeasures to integrate the cyclists in a safe and efficient way on two-lane rural roads.
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