Transit Signal Priority Strategy Based On Trajectory-Delay Estimation Under Connected Environment

With the urbanization and the substantial increasement of residents’ travel,problems such as traffic congestion are increasingly prominent,which have seriously affected urban development and the improvement of people’s living.Therefore,the development of advanced public transport system is so urgent that can solve these problems.According to statistical analysis,the transport capacity of a bus is equivalent to20-30 times that of passenger cars.The road occupied by ordinary passenger cars are about three times that of buses while Transporting the same transport volume.Therefore,the development of TSP(Transit-bus Priority System)is generally considered to be the best way for the sustainable development of urban transportation.On the one hand,the public transport priority strategy is carried out through the construction of bus lane,although it improves the traffic efficiency of public transport,it reduces the traffic capacity of passenger-vehicles;On the other hand,by optimizing the intersection signal timing scheme,the delay of bus is reduced.Most of early studies are based on traffic flow measurement,it is not accurate enough;Moreover,the comprehensive benefits of other passenger vehicles are less considered in previous studies,which reduces the feasibility of TSP strategy seriously.So that,this paper studies the TSP strategy at connected intersections by V2I(vehicle to everything)technology.The main contents include:1.By analysing the architecture of the current V2 I system and the data structure,acquisition method and application environment of various message sets in V2 I environment,the delay estimation process based on vehicle trajectory and signal timing data is designed.In the case of red light,the MEC(Mobile Edge Computing)uses the switching time of the current phase and the next phase,vehicle position and sequence,and then cooperates with the departure wave speed to calculate the estimated time point and position of vehicles joining and leaving the queue.In case of green light,the vehicles that cannot pass through the intersection are selected according to the end time of green light,and then the delay of these vehicles is calculated according to the method as like red light case.2.The total delay is weighted according to the number of passengers,then the benefit function is defined by the minimization of expected average delay,and a series of constraints and constrained feasible regions are set for the online optimization process to ensure that the optimization result conforms to the traffic signal machine phase switching logic,and then look up the optimal switching time of the preset phase through the hash table.2.According to the delay prediction method above,the hash table of status and delay value is established to simplify the single vehicle delay calculation process,the delay is weighted according to the number of passengers,and the benefit function is deduced by it.Some constraints are set for the online optimization process to restrict the feasible region,so as to ensure that the optimization result conforms to the phase switching rule,and finally send the command to the signal system.3.By investigating the road network structure and traffic flow of CV demonstration area in Wuhan Economic&Technological Development Zone,use SUMO(Simulation of Urban Mobility)to build a bus priority system based on traffic flow delay-prediction and trajectory delay-prediction method for signal control respectively.Then,the simulation result before and after optimization by two methods are analyzed.The experimental results show that under the conditions of low,medium and high flow and supersaturated flow,the bus delay of the improved method is reduced by 9.79%,25.43%,18.10% and 1.87% respectively;Without the improvement,it decreased by 7.0%,19.14%,17.81% and 2.34% respectively.The per capita delay of the improved method is reduced by 8.14%、19.88%、2.49% and 1.10% respectively,without the improvement,it decreased by 7.0%,19.14%,17.81% and 2.34%respectively.the change rates of all vehicles after improvement are-7.59%,-15.64%,4.05% and-1.47%.In the case of low and medium saturation,the strategy can basically the bus delay and bus travel time with ensuring the traffic benefits of non-priority vehicles.The improved method has a greater reduction in delay and a more stable effect.