For what number of cars must self organization occur in the   Biham-Middleton-Levine traffic model from any possible starting   configuration?
  For any initial configuration of fewer than N/2 cars the BML model will self organize to attain speed one. On the other hand, there is a configuration of size m in which no car can move if and only if m is at least 2N. 
Tim D. Austin (UC, Los Angeles), Itai Benjamini (Weizmann Institute)