The problem of optimizing traffic light phases dates back to the fifties. Since there, many solutions for different network configurations (isolated intersections, coordinated intersections, and so ...on) and different modeling and solution approaches (empirical models, queue theory approaches, mathematical programming models, etc.) have been proposed.
In parallel, it has been developed the general theory of hybrid systems, i.e., of those systems characterized by two kinds of states: normal states whose variation is governed by a fixed set of equations, and macro states whose change is governed by the occurrence of particular conditions or external events.
In this paper, a hybrid model of traffic light dynamics is introduced aiming at providing a modelling framework for evaluating the sensitivity of the performances of different approaches for signal setting optimal design.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The developments of telecommunication and intelligent transportation technologies have led to an increase in the safety level of freight transportation and have enabled making the routing decisions ...based on real-time information and an updated condition of the network, the suppliers, and the receivers. This paper proposes a dynamic decentralized optimization case, in which the network of freight distribution, presented as a distributed Supply Chain (DSC), expands or changes temporally. The proposed optimization problem should be solved repeatedly on a rolling horizon basis which enables optimizing a certain time period in advance. At each step, the problem is modeled using discrete event systems (DESs) and a transportation model is proposed for transferring freights between any two nodes of the supply chain. This model supports the decision making process for routing and scheduling of delivery shipments that arrive dynamically at a supplier, which is of major importance and directly affects the performance of a freight distribution system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A novel hybrid model for transportation systems is proposed, in which the functioning is represented via a continuous-time model whenever no changes in the traffic flow occur, whereas the changes in ...the system behaviour are modelled through a discrete event system coupled with the continuous-time system. Via the discrete-event part of the hybrid model, its continuous-time part is adapted according to the variation occurred in the system behaviour. The hybrid modelling methodology proposed is based on the use of a special class of Petri nets, the hybrid stochastic Petri nets (HSPN). These nets are composed of some discrete parts, and some continuous parts, so that a hybrid Petri net can be viewed as a combination of an usual (discrete) Petri net and a continuous Petri net, the 'fluid' version of usual timed Petri nets. The discrete part of the HSPN 'regulates' the continuous PN, which models the functioning of the transportation system. This results in the model reacting to any change to the current system behaviour by adapting the traffic parameters to the new state.
Rapid urbanization along with the population growth increases the pressure on existing transportation systems which boosts the needs for the provision of a well-connected and efficient Public ...Transport Systems (PTSs) to meet the mobility needs of the people. In this framework, it is important for the PTSs of a region to perform at certain quality levels including availability (both spatial and temporal), accessibility, affordability, environmental protection etc. Among all these features, the most important is the accessibility to stops since access to/from the public transport is provided only through them. This paper is focused on the development of a novel methodology to evaluate the accessibility of public transport at different levels of measurements of a region/ city using Public Transport Accessibility Index (PTAI). It is developed based on the accessibility of public transport stops to the population, service centers and connectivity to nearby regions. The proposed approach is effective in terms of highlighting the least accessible areas towards the improvement of existing public transport connections or planning of new services. An application of proposed methodology has been presented using a mathematical example.
A new freeway traffic model is presented, which is made up by two modeling levels. The regular traffic conditions are represented by means of a macroscopic multiclass model, whereas the nonrecurrent ...situations are described in terms of discrete events. The necessary synchronization mechanisms are sought for the overall model to allow it to be used as a simulation model, and some comments on how to statistically treat the real-world traffic data in order to obtain suitable input functions for the simulator are reported. The comparison between the real and the simulated evolution of some relevant traffic variables is provided to give a feeling of the model experimental validation phase.
Describes a hierarchical two level modeling and control framework for real-time manufacturing processes, based on hybrid Petri nets, and capable of integrating monitoring and fault detection ...techniques along with performance optimization procedures. At the higher level, first-order hybrid Petri nets are used to generate the asynchronous concurrent events characterizing the nominal optimal system behavior, also providing the machine production rates. At the lower level, a real time scheduler and a discrete Petri net communicate with the field-bus devices to force the machine to produce at the rates provided by the upper level, and monitor the occurring events by keeping track of part movements. Whenever a process failure is detected, the diagnosis procedure is triggered, and a recovery sequence is imposed.
A model of manufacturing systems is considered in which several classes of products are repeatedly manufactured, according to the requirements specified by customer orders. The problem considered is ...the development of control strategies capable of reacting to deviations of the system behaviour from a nominal behaviour defined solving a suitable problem at the scheduling level. The degrees of freedom allowed for the control problem are: the execution times of some elementary operations, the lot-sizes, and the variables expressing the timing of the production process. It is shown that, under suitable hypotheses about the nominal behaviour, the system can be represented by means of a particular class of timed Petri nets. Moreover, the structure of the control problem is that of a continuous variable problem with quadratic cost and linear (or sometimes quadratic) constraints.
We are on the verge of a new revolution for road transportation: automated, automatic, and/or connected vehicles will soon be seen moving people and freight in urban areas and on motorways as well, ...likely supporting the spread of both shared and electric vehicles among travelers. But to turn all the existing stock of traditional human-driven vehicles, most often privately owned, will presumably take several years. Meanwhile both technologies will co-exist and share the same facilities. The evaluation of the impacts on network performance and user behavior requires enhancements of the tools of the traffic and transportation theory already available to modelers and planners. This paper proposes a general overview of existing methods for traffic analysis and control and for transportation systems analysis and design to test whether they can still be applied as such, or with straightforward enhancements, or new tools are needed.
Signalized urban areas are microscopically represented by means of deterministic-timed Petri nets (DTPNs), with the purpose of providing a suitable modelling tool for traffic management and ...signalling control. The model described in this paper consists of signalized intersections and roads. In order to properly model traffic congestion, intersections are divided into several crossing sections. An intersection always includes a multi-stage traffic signal, whose stage matrix (i.e., the sequence of signal stages) is a-priori known. The DTPN representing the traffic model, intended to traffic management and signalling control, is proposed and fully described in the paper.
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