  Since the first reported traffic jam about a century ago, traffic congestion
has been intensively studied with various methods ranging from macroscopic to
microscopic viewpoint. However, due to the population growth and fast
civilization, traffic congestion has become significantly worse not only
leading to economic losses, but also causes environment damages. Without
understanding of jams spatio-temporal propagation behavior in a city, it is
impossible to develop efficient mitigation strategies to control and improve
city traffic. Although some progress has been made in recent studies based on
available traffic data regarding general features of traffic, the understanding
of the spatio-temporal propagation of traffic jams in urban traffic is still
unclear. Here we study the spatio-temporal propagation behavior of traffic jams
based on collected empirical traffic data in big cities. We developed a method
to identify influential jam centers and find that jams spread radially from
multiple jam centers with a range of velocities. Our findings may help to
predict and even control the traffic jam propagation, which could be helpful
for the development of future autonomous driving technology and intelligent
transportation system.
