(a) Relationship between initial distance dis and disturbance rate D in the time period [0,300 s] with the condition f = 0.1 m. D_l and t_l here mean the lowest quantity of D and the time achieving that in the process. (b) Distribution of D_l with variable f f. dis_c shows that when initial distance dis > dis_c with one certain f f, D keeps at 1 all the time, i.e., no observable disturbance exists in the queue. (c) Distribution of time t_l when relative D_l is obtained.