Research On Vehicle Scheduling Optimization For Hazardous Materials Road Transportation On The Basis Of Space-time Coordination

As a special-type cargo,hazardous materials may lead to serious consequences such as combustion,explosions and leaks once an accident occurred in the transportation link,which could cause casualties,property losses,and environmental pollution etc.Optimal routing of hazardous materials is considered as one of the important measures to reduce the risk of hazardous materials transportation,and the transport route with the lowest accidents' probability is selected in order to reduce the risks of impacting on the population and environment along the route as possible.However,multiple vehicles will increase the potential risks when they are used simultaneously.Based on optimal routing,the vehicles can be scientifically and rationally scheduled and the additional potential risks can be eliminated,so that the transport risk can be reduced dramatically.Therefore,it is quite necessary to study the vehicle scheduling optimization for hazardous materials road transportation.Vehicle scheduling is a difficult problem in the field of hazardous materials transportation.Most of the existing researches are based on the transportation risk impact by the time-varying characteristics of the path,fix the driving path and departure time while they do not take into account of the potential risks of the interaction among vehicles.Aimed at static and time-varying hazardous materials transportation networks in this thesis,respectively,vehicles' space-time dissimilarity is portrayed from three aspects,including dissimilarity of paths and nodes,and space-time safety distance.Besides,a series of research on transportation vehicle scheduling for hazardous materials road transportation is carried out using space-time coordination optimization.The main contents of this thesis are as follows:(1)Vehicle scheduling problem of hazardous materials transportation on dissimilar paths.A T* hazardous materials transportation network constructing method,being different from the traditional ones,is proposed and it can express the coupling relationship and show the dissimilarity measure among paths.In addition,the solution method of maximum independent set problem of graphs is introduced to obtain the dissimilar paths in the network,so that the path in the filtered dissimilar path set can be selected.As a result,vehicles can keep safe distance during transportation process by adjusting the departure time on each route in accordance with the safety interval.(2)Vehicle scheduling problem of hazardous materials transportation considering the nodes' space-time dissimilarity.The space-time coordinating scheduling method is used to schedule hazardous materials transportation vehicles and,by adjusting the departure time interval,hazardous materials transportation vehicles can maintain a safety distance at the common nodes(or common road sections)when passing the ?non-dissimilar? route,and achieve the purpose of space-time dissimilarity.Considering the space-time dissimilarity can make up of the insufficiency of the dissimilarity path method in vehicle scheduling and avoid missing the optimal transportation path as well.(3)Vehicle scheduling problem of hazardous materials transportation considering the space-time safety distance.A method of calculating the space-time distance between hazardous materials transportation vehicles based on the concept of space-time distance in Space Physics is proposed and the departure time interval of vehicles can be calculated according to the space-time safety distance.A kind of hazardous materials vehicle scheduling model meeting the time-space dissimilar conditions among ODs is established and a two-stage solution method is designed to generate the vehicle schedules.The starting time of the vehicle scheduling getting by this method can not only ensure that the vehicles always maintain a safety distance at common nodes,but also meet the requirements that the vehicles in the network can maintain a safety distance at any time when moving.(4)Vehicle scheduling problem of hazardous materials transportation in the time-varying network.In order to optimize the vehicle routing under time-varying conditions,a time-varying pulse algorithm is designed to solve the bi-objective shortest path problem and it can obtain the optimal path set of Pareto at different departure time.After selecting the path in the obtained Pareto optimal path set,a vehicle scheduling model considering the space-time safety distance among hazardous materials transportation vehicles is constructed.The multi-objective optimization algorithm is designed to obtain the vehicle schedules.Decision-makers can choose a reasonable transportation route and departure time based on their risk appetite on one hand,and can keep the space-time dissimilarity of vehicles along the whole route on the other.(5)Vehicle scheduling problem of hazardous materials transportation considering the risk equity.In order to reduce the differences in risk distribution among the population aggregation areas during the hazardous materials transportation,a vehicle-scheduling model is built considering the risk fairness.Meanwhile,a two-stage optimization algorithm with decision-makers' participation is designed to solve the problem,so as to obtain a ?periodic? scheduling scheme with the best risk fairness in the transportation process of a group of hazardous materials.Thanks to the decision-maker's participation,the calculating efficiency can be enhanced and the decision-maker's appetite can be cared.The vehicle scheduling problem of hazardous materials road transportation is studied by use of space-time coordination optimization method.In the aspect of spatial dissimilarity,a new method of network construction is proposed,and the maximum independent set method is introduced to obtain the dissimilarity path in the hazardous materials transportation network,and a new idea solving the problem of dissimilarity path is proposed.As for space-time dissimilarity,the relationship between the impact of vehicle accidents of other vehicles and the space-time distance are analyzed,and a representation method with space-time dissimilarity of nodes and space-time safety distance is proposed.The problem is reconstructed into a space-time combination optimization problem with a constraint based on the departure time interval,and the mathematical model of vehicle scheduling optimization under the conditions of space-time dissimilarity is discussed,and a multi-objective optimization method for vehicle scheduling problem of the hazardous materials transportation is studied.Additionally,for the materials transportation in time-varying networks,a time-varying pulse algorithm is designed to solve the bi-objective shortest path problem,which can efficiently obtain the Pareto-optimal path.Corresponding to the drawbacks of risk equity by vehicle routing,a vehicle scheduling optimization model considering risk equity is built,and the vehicle scheduling scheme is obtained by adjusting the frequency of using the path,which makes up of the lack of true positive risk fairness causing by the path optimization.Hence,a series of researches on the vehicle scheduling for hazardous materials road transportation is carried out using methods of problem analysis,model construction and algorithm design so that the conclusions can provide vehicle scheduling decision guidance for hazardous materials carriers.