  The Biham-Middleton-Levine model (BML) is simple lattice model of traffic
flow, self-organization and jamming. Rather than a sharp phase transition
between free-flow and jammed, it was recently shown that there is a region
where stable intermediate states exist, with details dependent on the aspect
ratio of the underlying lattice. Here we investigate square aspect ratios,
focusing on the region where random, disordered intermediate (DI) states and
conventional global jam (GJ) states coexist, and show that DI states dominate
for some densities and timescales. Moreover, we show that periodic intermediate
(PI) states can also coexist. PI states converge to periodic limit cycles with
short recurrence times and were previously conjectured to arise from
idiosyncrasies of relatively prime aspect ratios. The observed coexistence of
DI, PI and GJ states shows that global parameters, density together with aspect
ratio, are not sufficient to determine the full jamming outcome. We investigate
additional features that lead towards jamming and show that a strategic
perturbation of a few selected bits can change the nature of the flow,
nucleating a global jam.
