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Trajectory planning is of great value and yet challenging for multirotor unmanned aerial vehicle (UAV) applications in a complex urban environment, mainly due to the complexities of handling cluttered obstacles. The problem further complicates itself in the context of autonomous multi-UAV trajectory planning considering conflict avoidance for future city applications. To tackle this problem, this paper introduces the multi-UAV cooperative trajectory planning (MCTP) problem, and proposes a bilevel model for the problem. The upper level is modeled as an extended multiple traveling salesman problem, aiming at generating trajectories based on heuristic framework for multi-UAV task allocation and scheduling and meanwhile considering UAV kinodynamic properties. The lower level is modeled as a holding time assignment problem to avoid possible spatiotemporal trajectory conflicts, where conflict time difference is analyzed based on the proposed state-time graph method. Numerical studies are conducted in both a 1
Kaiping Wang; Mingzhu Song; Meng Li. Cooperative Multi-UAV Conflict Avoidance Planning in a Complex Urban Environment. Sustainability 2021, 13, 6807 .
AMA StyleKaiping Wang, Mingzhu Song, Meng Li. Cooperative Multi-UAV Conflict Avoidance Planning in a Complex Urban Environment. Sustainability. 2021; 13 (12):6807.
Chicago/Turabian StyleKaiping Wang; Mingzhu Song; Meng Li. 2021. "Cooperative Multi-UAV Conflict Avoidance Planning in a Complex Urban Environment." Sustainability 13, no. 12: 6807.
The accessibility of transit stops (ATS) is a critical index for the evaluation of transit service, focusing on the first/last mile portions of transit trips. It is significantly affected by feeder modes, such as walking and cycling. Comparison of the application of different modes has been addressed in previous research, thus there is mostly only one feeder mode considered in this case study. This study has proposed a model for ATS with multiple feeder modes (ATSMFM), capable of integrating multiple feeder modes and considering the heterogeneity of travellers from the perspective of city managers. It is a bi-level model, combining cumulative and utility-based approaches. The final form of ATSMFM is developed referring to the cumulative approach, while the determination of the catchment area is utility-based. A numerical experiment has been conducted to demonstrate the necessity and applicability of ATSMFM. The results show that the ATS with a single feeder mode, such as cycling or walking, underestimates the catchment area of nearly one-third or two-thirds of travellers. As for ATSMFM, this proposed approach can automatically select the feeder mode from alternatives according to traveller attributes, thus removing the limitation of a single feeder mode, and is suitable for calculating ATS in the complex environment with multiple feeder modes. Besides, the ATSMFM model can support city managers with different emphases in transit planning via flexibly setting the threshold.
Mingzhu Song; Yi Zhang; Meng Li; Yi Zhang. Accessibility of Transit Stops with Multiple Feeder Modes: Walking and Private-Bike Cycling. Sustainability 2021, 13, 3522 .
AMA StyleMingzhu Song, Yi Zhang, Meng Li, Yi Zhang. Accessibility of Transit Stops with Multiple Feeder Modes: Walking and Private-Bike Cycling. Sustainability. 2021; 13 (6):3522.
Chicago/Turabian StyleMingzhu Song; Yi Zhang; Meng Li; Yi Zhang. 2021. "Accessibility of Transit Stops with Multiple Feeder Modes: Walking and Private-Bike Cycling." Sustainability 13, no. 6: 3522.
The presence of bike-sharing has a significant influence on the ease of trips by bike, which is one critical aspect of bicycling accessibility (BAcc). The existing measurements of BAcc rarely consider the factor of ownership of bikes, which means that no distinction is made between private-bikes and shared bikes. To measure BAcc more fully, this paper proposes a method to evaluate the influences of bike-sharing on BAcc and to perform the method on a real-world case study in Beijing. It is found that bike-sharing has a boosting effect on BAcc, and the increased rate of BAcc is significantly affected by bicycling frequency and shared-bike availability. A case study in Beijing utilizing geo-location data collected from two major bike-sharing companies (OFO and Mo-bike) illustrates the significance of the impact of bike-sharing on BAcc and the necessity to include bike-sharing in the measurement of BAcc. Besides, the case study shows BAcc around the transit station is better than that over the whole area. Given that bicycling feeds transit, this research lays the foundation for analyzing the combination of bike-sharing and transit from the perspective of accessibility and can further support transportation planning.
Mingzhu Song; Kaiping Wang; Yi Zhang; Meng Li; Qi He; Yi Zhang. Impact Evaluation of Bike-Sharing on Bicycling Accessibility. Sustainability 2020, 12, 6124 .
AMA StyleMingzhu Song, Kaiping Wang, Yi Zhang, Meng Li, Qi He, Yi Zhang. Impact Evaluation of Bike-Sharing on Bicycling Accessibility. Sustainability. 2020; 12 (15):6124.
Chicago/Turabian StyleMingzhu Song; Kaiping Wang; Yi Zhang; Meng Li; Qi He; Yi Zhang. 2020. "Impact Evaluation of Bike-Sharing on Bicycling Accessibility." Sustainability 12, no. 15: 6124.