Key points are not available for this paper at this time.
Sugiyamal Y., Fukui M., Kikuchi M., et al. Traffic jams without bottlenecks-experimental evidence for the physical mechanism of the formation of a jam. New Journal of Physics 10, 033001 (2008); https://doi.org/10.1088/1367-2630/10/3/033001.
Sugiyama et al. (Tue,) studied this question.