Optimization Method Of Inter-Stop Operating Speeds For Autonomous Electric Buses With Dedicated Lane

Due to the fact that electric vehicles have "zero emissions" and "high energy efficiency" during operation,and autonomous driving technology has advantages in terms of safety,efficiency,and comfort,the process of electrification and automation for buses has become current development trend.Unlike manually driven buses,autonomous electric buses(AEBs)usually operate on dedicated bus lanes,relying on onboard autonomous driving systems to control the operating speeds and precisely control their own motion state,which in turn limits the number of acceleration and deceleration,reduces energy consumption and decreases travel times.By optimizing the operating speeds of AEBs,passenger comfort,vehicle economy and punctuality can be effectively improved,which is important to promote the electrification and automation of buses and improve the attractiveness of public transportation systems.However,when implementing unreasonable operating speed schemes,an AEB may frequently accelerate and decelerate,encounter red lights at signalized intersections,or even fail to maintain a reasonable headway with other AEBs.Under such circumstances,AEBs will face problems such as high energy consumption and long travel times,which greatly hinder their further promotion and application.In single-route scenarios,AEB operating speeds are influenced by factors such as stochastic dwell times of vehicles at stops and signal timing schemes at intersections.While in multi-route scenarios,bus operating speeds are also closely related to the interaction among buses.Therefore,this paper takes the trip between adjacent stops as the research scope,divides the research environment into single-route and multi-route,and proposes the optimization method of inter-stop operating speeds of AEBs under two scenarios.First,this paper investigates the optimization method of inter-stop speeds for AEBs operating on a single route.In order to exclude the stochastic fluctuation of bus departure times caused by stochastic dwell times,the trip between two adjacent stops is determined as the optimization scope.In addition,the inter-stop speeds are divided into several stages to simulate the "uniformly variable motion,uniform motion,and uniformly variable motion",and each speed stage is described by two parameters: target speed and duration time.When the target bus is about to depart from the stop,the operating speeds is optimized for the inter-stop trip.Based on the above optimization process,the bus departure time,signal timing schemes of intersections,and inter-stop trip information are considered to establish the inter-stop operating speed functions with the phase operating parameters as input.So that the actual inter-stop operating speed function can be constructed for the construction of the economy index and punctuality index.Based on this,a multi-objective optimization model is established with the phase operating parameters as the optimization variables and the highest vehicle economy and punctuality of the target AEB as the objective functions,and a multiobjective particle swarm optimization algorithm(MOPSO)is used to solve the model.Immediately after,an optimization method of inter-stop speeds for AEBs operating on multiple routes is proposed.Similar to the single-route scenario,the inter-stop operating speed described by the phase operating parameters is optimized when the target bus is about to depart from the stop;the difference is that the speeds of target AEB and buses on the upstream inter-stop trip are jointly optimized in order to obtain higher vehicle economy and punctuality.According to the optimization process,the departure time of the target bus is a deterministic parameter,while the departure times of the rear buses fluctuate randomly due to the stochastic dwell times at the stop.Therefore,firstly,different base inter-stop operating speed functions are established for the target bus and the rear bus with the phase operating parameters as input,and the headways are judged to be reasonable.Immediately after that,the following behaviors of the AEBs is modeled,and the final inter-stop operating speed modification algorithm considering the following behaviors is proposed for the AEBs with unreasonable headway.Finally,a chance-constrained programming model is established with phase operating parameters of all buses as optimization variables and the highest vehicle economy and punctuality as objective functions.The MOPSO algorithm with embedded stochastic simulation technique is used to solve the model for its multiobjective and nonlinear characteristics and the input of stochastic parameters.Finally,this paper uses actual bus routes as examples and verifies the effectiveness of the proposed methods,respectively.Results indicated that:(i)the proposed singleroute AEB inter-stop operating speed optimization method can flexibly support different signal phase and timing of signalized intersections,and can ensure the improvement of punctuality without increasing energy consumption compared with three baseline methods;(ii)the proposed single-route AEB inter-stop operating speed optimization method can generate an effective operating speed scheme in the presence of stochastic bus departure times.If the target inter-stop trip contains no signalized intersections or signalized intersections with a higher green ratio,the optimization effect of this method is basically the same as that of the compared method.If the target inter-stop trip contains more signalized intersections or signalized intersections with a lower green ratio,this method achieves a better optimization effect that the AEB’s vehicle economy index and the punctuality index are both reduced.