Simulation results of the bi-directional pedestrian movement for (a)–(c)f= 0.01 and (d), (e)f= 0.1 with the numbers of up walkers of (a) 66, (b) 76, (c) 221, (d) 151, and (e) 226. The number of down walkers equals that of up walkers. The green circles represent down walkers and the pink circles indicate up walkers.