Phase based jam warnings: an analysis of synchronized flow with floating car data

Based on an empirical study of floating car data (probe vehicle data), we have found the following microscopic features of empirical synchronized flow that are relevant for jam warning methods: (i) In accordance with Kerner’s three-phase traffic theory, the empirical speed decrease (speed drop) denoted by Δv that occurs due to vehicle deceleration at the upstream front of synchronized flow is a complex time function. (ii) The empirical function Δv can be considered a “jam wall” at which different vehicles exhibit sometimes very different speed drops Δv occurring at different road locations. Because each of the vehicles decelerates within the “jam wall” at different road locations, the “jam wall” moves in space and in time. (iii) The spatiotemporal structure of the empirical “jam wall” is determined by alternations of the synchronized flow and wide moving jam traffic phases at the upstream front of a congested traffic pattern. (iv) During some time intervals, the “jam wall” can disappear and then it can appear once more, and so on; during “jam wall” disappearance, one or a few vehicles can pass a bottleneck while moving in free flow. These empirical findings can be important for the development of reliable jam warning methods as well as other ITS-applications.