random orientation pointing outwards, and the persistence of its motion is high enough, it will interact with less neighbors as its persistent motion proceeds and eventually leave the cluster. The way particles are structured in a band makes it more robust against escape processes as the one just described. As illustrated in Fig. \[fig:laneband\], a random re-orientation of a particle in the surface of a band cannot lead to a reduction of the number of neighbors. However, because of the persistence of the particles motion and the small inter-particle spacing, random fluctuations of the orientation induce further hard-core collisions (see overlapping disks in Fig. \[fig:laneband\]). This enhancement of collisions in the bulk and forefront of a traveling (dense) band introduces extra fluctuations which might destabilize it, resulting in the coexistence (or bistability) of lanes and bands observed in the high $\text{Pe}$ regime (see Fig. \[fig:Pxy\] and Movie 2 and 3 in [@SM]). A random fluctuation of the orientation of a particle may leave an empty space that, in turn, may help another particle to escape. This is a simple illustration of the intricate coupling between density and polarization fluctuations at short length scales due to the presence of volume exclusion. 