F → S → F Transitions in Vehicle Probe Data

Based on a study of probe vehicle data we have revealed empirical F→S→F transitions before traffic breakdown at the bottleneck theoretically predicted by Kerner. Anonymized probe data from connected vehicles of a large fleet have been collected. The frequency of connected vehicles in our study has been more than ten times larger (on average about 10 s between probe vehicles) than in earlier studies. This data shows that disturbances in free flow evolve in a neighbourhood of the bottleneck leading to small regions of synchronized flow (F→S transition). These regions of synchronized flow dissolve after a random amount of time (traffic recovers to free flow (S→F transition)) before the traffic breakdown occurs. In contrast with the F→S→F transitions, traffic breakdown leads to a long-living congested traffic pattern propagating upstream of the bottleneck. The empirical findings of this paper support some of the theoretical features of the S→F instability.