As mentioned, the main reason of Kerner’s three-phase traffic theory is the explanation of the empirical nucleation nature of traffic breakdown (F → S transition) at the bottleneck. To reach this goal, in congested traffic a new traffic phase called synchronized flow has been introduced. The basic feature of the synchronized flow traffic phase formulated in the three-phase traffic theory leads to the nucleation nature of the F → S transition. In this sense, Kerner’s synchronized flow traffic phase that ensures the nucleation nature of the F → S transition at a highway bottleneck and Kerner’s three-phase traffic theory can be considered synonyms.