This paper studies slow-to-start effect in two-dimensional Biham–Middleton–Levine (BML) traffic flow model with traffic light periods T=2τ. In most cases, the model exhibits free flow, jam, and phase separation phenomenon. Nevertheless, when the slow-to-start parameter p=0, and traffic light parameter τ=3 or 5, it is found that phase separation phenomenon does not occur. We have explained this via the evolution process from a designed regular initial configuration. Moreover, it is also found that the free flow self-organizes into grid-like structure when τ is large and the slow-to-start parameter 0<p<1.