Study On Time-varying Vehicle Routing Problems Considering Traffic Congestion

With the acceleration of urbanization,the problem of traffic congestion is becoming more and more serious.At the same time,due to the low speed of vehicles when they are congested,frequent acceleration or deceleration,resulting in a sharp increase in fuel consumption and carbon dioxide emissions,has a significant impact on the environment.In order to ease traffic congestion,local governments have issued policies to restrict large trucks,which has caused logistics companies to move their distribution centers to the outskirts of the city.Therefore,the classic distribution model has been unable to meet the new trend of development,and has traveled a two-level distribution model.Grades are transported by large trucks between cities,and second grades are delivered by trucks in urban areas that are restricted to travel.The first-level route is long-distance transportation,so time-varying is not taken into consideration;the second-level route occurs in a traffic congested urban area,and it needs to consider time-varying.The traditional static vehicle route problem does not consider the time-variation of the road network.The actual traffic network is more complex and the vehicle's travel speed also varies with time and road sections.Based on the background of traffic jams,this paper studies the problem of two-level vehicle routing,in which the speed changes with time under real-time road traffic conditions,so it has very important practical significance.First of all,through the summary of the domestic and foreign literatures on the time-varying vehicle routing problem and the two-level vehicle routing problem,we understand the background of the study and put forward the research direction.In the two-level delivery model,the first-order path does not consider time-varying,and the travel speed of the second-level path vehicle changes with the departure time.This paper comprehensively considers the impact of distance,time,load,and fuel factors on costs.A method for calculating the travel speed across the time domain is proposed,and a mathematical model with cost as an optimization goal is established.Due to the high complexity of the model,higher requirements are imposed on the efficiency and quality of the algorithm's solution.Therefore,based on the genetic algorithm,this paper adopts random all-arrangement to generate the initial population,improves the crossover and mutation operator,and uses two successively modified operators to exchange customers.Positions,improve the solution performance of the algorithm,and then combined with the top-down solution ideas,design hybrid genetic algorithm,first use the conservation algorithm to obtain the first-level path,and then use the improved genetic algorithm to solve the second-level path.Finally,the feasibility and effectiveness of the two-level delivery model under time-varying network are fully verified by examples of e-commerce companies.The results show that the cost-optimized model comprehensively considers factors such as distance,time,vehicle load,and fuel.Efficient and rational distribution plan.From the perspective of logistics companies,studying the two-level vehicle routing problem under time-varying networks can effectively reduce logistics costs,increase efficiency,and greatly reduce greenhouse gas emissions.From a social perspective,two-tier distribution models eased traffic jams and environmental problems and improved people's quality of life.