141,171 research outputs found
Optimized energy management of inductively charged electric buses reflecting operational constraints and traffic conditions
The introduction of alternative propulsion concepts in public transport makes significant contributions to further reduce pollutants emitted by transport systems (noise, air pollutants). This paradigm shift is a major challenge for public transport operators. Operational performance of heavy duty vehicles depends on many different factors such as climatic conditions, load profiles (e.g. variations in passenger occupancy) and track topology. Currently there is no common standard which allows the assessment of energetic performance of different vehicle concepts and optimum deployment strategies of electric charging infrastructure in the network (with respect to their impact on the vehicles’ duty plans). This paper introduces a simulation-based approach to provide answers to this multi-variant optimization problem. The model outlined in this paper allows operators to choose the most adequate vehicle type(s) and corresponding infrastructure for their respective conditions aiming at a maximum operational availability of the buses during the operational day. Furthermore, the simulation model allows the assessment of time tables and line topologies with respect to their operational feasibility. This paper discusses experiences made with simulative studies in the introduction of inductively charged electric buses in the city of Braunschweig (Germany)
Optimal Alignments for Designing Urban Transport Systems: Application to Seville
The achievement of some of the Sustainable Development Goals (SDGs) from the recent
2030 Agenda for Sustainable Development has drawn the attention of many countries towards
urban transport networks. Mathematical modeling constitutes an analytical tool for the formal
description of a transportation system whereby it facilitates the introduction of variables and the
definition of objectives to be optimized. One of the stages of the methodology followed in the
design of urban transit systems starts with the determination of corridors to optimize the population
covered by the system whilst taking into account the mobility patterns of potential users and the
time saved when the public network is used instead of private means of transport. Since the capture
of users occurs at stations, it seems reasonable to consider an extensive and homogeneous set of
candidate sites evaluated according to the parameters considered (such as pedestrian population
captured and destination preferences) and to select subsets of stations so that alignments can take
place. The application of optimization procedures that decide the sequence of nodes composing the
alignment can produce zigzagging corridors, which are less appropriate for the design of a single line.
The main aim of this work is to include a new criterion to avoid the zigzag effect when the alignment
is about to be determined. For this purpose, a curvature concept for polygonal lines is introduced,
and its performance is analyzed when criteria of maximizing coverage and minimizing curvature are
combined in the same design algorithm. The results show the application of the mathematical model
presented for a real case in the city of Seville in Spain.Ministerio de Economía y Competitividad MTM2015-67706-
Towards a Testbed for Dynamic Vehicle Routing Algorithms
Since modern transport services are becoming more flexible, demand-responsive, and energy/cost efficient, there is a growing demand for large-scale microscopic simulation platforms in order to test sophisticated routing algorithms. Such platforms have to simulate in detail, not only the dynamically changing demand and supply of the relevant service, but also traffic flow and other relevant transport services. This paper presents the DVRP extension to the open-source MATSim simulator. The extension is designed to be highly general and customizable to simulate a wide range of dynamic rich vehicle routing problems. The extension allows plugging in of various algorithms that are responsible for continuous re-optimisation of routes in response to changes in the system. The DVRP extension has been used in many research and commercial projects dealing with simulation of electric and autonomous taxis, demand-responsive transport, personal rapid transport, free-floating car sharing and parking search
A dynamic approach to rebalancing bike-sharing systems
Bike-sharing services are flourishing in Smart Cities worldwide. They provide a low-cost and environment-friendly transportation alternative and help reduce traffic congestion. However, these new services are still under development, and several challenges need to be solved. A major problem is the management of rebalancing trucks in order to ensure that bikes and stalls in the docking stations are always available when needed, despite the fluctuations in the service demand. In this work, we propose a dynamic rebalancing strategy that exploits historical data to predict the network conditions and promptly act in case of necessity. We use Birth-Death Processes to model the stations' occupancy and decide when to redistribute bikes, and graph theory to select the rebalancing path and the stations involved. We validate the proposed framework on the data provided by New York City's bike-sharing system. The numerical simulations show that a dynamic strategy able to adapt to the fluctuating nature of the network outperforms rebalancing schemes based on a static schedule
Adaptive performance optimization for large-scale traffic control systems
In this paper, we study the problem of optimizing (fine-tuning) the design parameters of large-scale traffic control systems that are composed of distinct and mutually interacting modules. This problem usually requires a considerable amount of human effort and time to devote to the successful deployment and operation of traffic control systems due to the lack of an automated well-established systematic approach. We investigate the adaptive fine-tuning algorithm for determining the set of design parameters of two distinct mutually interacting modules of the traffic-responsive urban control (TUC) strategy, i.e., split and cycle, for the large-scale urban road network of the city of Chania, Greece. Simulation results are presented, demonstrating that the network performance in terms of the daily mean speed, which is attained by the proposed adaptive optimization methodology, is significantly better than the original TUC system in the case in which the aforementioned design parameters are manually fine-tuned to virtual perfection by the system operators
Methodology for an integrated modelling of macro and microscopic processes in urban transport demand
The paper presents the theoretical formulation and the underlying assumptions for an activity-based approach of transport demand modelling. Starting with the definition of a time hierarchy of decision-making in the urban environment, rules are formulated that dictate the general hierarchic structure of individuals’ choices in the urban system. The temporal scale defines decisions for activities and their daily sequence, the geographical scale decisions associated to destination choice processes. We build activity plans (number and daily sequence of activities) from an empirical data set and calculate trip paths (time-spatial trajectories including transport modes and travel destinations) assuming consumers to maximize their utility in the decision-making process. First results of the translation of the theoretical model into a real-world application are shown for the city of Santiago, Chile
Fluctuation-driven capacity distribution in complex networks
Maximizing robustness and minimizing cost are common objectives in the design
of infrastructure networks. However, most infrastructure networks evolve and
operate in a highly decentralized fashion, which may significantly impact the
allocation of resources across the system. Here, we investigate this question
by focusing on the relation between capacity and load in different types of
real-world communication and transportation networks. We find strong empirical
evidence that the actual capacity of the network elements tends to be similar
to the maximum available capacity, if the cost is not strongly constraining. As
more weight is given to the cost, however, the capacity approaches the load
nonlinearly. In particular, all systems analyzed show larger unoccupied
portions of the capacities on network elements subjected to smaller loads,
which is in sharp contrast with the assumptions involved in (linear) models
proposed in previous theoretical studies. We describe the observed behavior of
the capacity-load relation as a function of the relative importance of the cost
by using a model that optimizes capacities to cope with network traffic
fluctuations. These results suggest that infrastructure systems have evolved
under pressure to minimize local failures, but not necessarily global failures
that can be caused by the spread of local damage through cascading processes
On green routing and scheduling problem
The vehicle routing and scheduling problem has been studied with much
interest within the last four decades. In this paper, some of the existing
literature dealing with routing and scheduling problems with environmental
issues is reviewed, and a description is provided of the problems that have
been investigated and how they are treated using combinatorial optimization
tools
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