Highway traffic fluctuations impact congestion durations (Vol. 48, No. 5-6)

Traffic flow time series (vehicles per minute) during one day on a highway in Germany, with two rush hours and strong fluctuations

Many highways around large cities are running above their capacity, leading to congested traffic. A useful statistical description of congestion distinguishes three phases: Free flow, synchronized traffic and wide moving jams. Traffic breakdown from free flow becomes increasingly likely around a critical flow (a certain number of vehicles per minute, specific for the highway section). Here we investigate the influence of flow fluctuations on congestion durations. As can be seen in the figure, traffic flow is antipersistent: It shows large fluctuations on short time scales which quickly trend back to the mean value, i. e. they reverse fast. Therefore, the duration of times with a flow above a critical value (here 60 vehicles per minute) is most oftenly a few minutes, but sometimes it extends over longer intervals up to several hours. We find that durations of congested traffic behave in the same way, and we conclude that traffic flow fluctuations are an important factor in congestion dynamics. The large number of short-lasting traffic jams implies a large risk for rear-end collisions.

S. M. Krause, L. Habel, Th. Guhr and M. Schreckenberg, The importance of antipersistence for traffic jams, EPL 118, 38005 (2017)