traffic-flow-dynamics.org/traffic-states

Traffic Jams: A Collective Phenomenon in Space and Time

Probably everybody knows traffic jams by his or her own experience. However, when driving through (or being stuck in) a congestion, one experiences only a small fraction of the jam. In reality, traffic congestions are collective spatiotemporal phenomena, often extending over many kilometers, and sometimes over several hours.

So we wonder how a jam would look like from the "bird's eye view". Are there several characteristic types of jams? What are the commonalities, what the differences? What are the influencing factors for a traffic breakdown? Is there such a thing as a "phantom traffic jam"?

These questions about the dynamics of vehicular traffic flow in space and time is the motivation for setting up this web presentation. They will be illustrated by means of empirical examples and an expansive searchable image database of real congestions .

Illustration of the Spatiotemporal Dynamics

Spatiotemporal Dynamics

An example from the image database is shown in this figure. Illustrated is the local speed (color-coded) of the vehicles driving at a given location (y axis) and a given time instant (x axis), averaged over all lanes. The speed has been determined from one-minute detector data by a dedicated method .

The figure shows congested traffic on the German freeway A5-South near Frankfurt. The congestions are caused by traffic breakdowns at the intersections "Friedberg" and "Bad Homburg", and (probably caused by an accident) at road kilometer 476. Notice that all congested regions exhibit traffic waves which propagate against the direction of travel (at about 15 km/h). The initially independent two congested areas merge to a complex congestion at about 9:00h and "activate" a third bottleneck at about kilometer 471.

Traffic Jam Image Database

Traffic Jam Image Database

After entering a driving direction (North or South) in the search mask to the left, you can display and search the congestions on the A5 during six months in the mid of 2001 (see also the seach hints).

This freeway section is one of the most investigated in traffic science since it provides a high number of densily spaced induction loop detectors. Moreover, traffic breakdowns occur frequently.

In the meantime, the capacity of this section has been greatly improved by adding a forth lane in each direction, and by an improved traffic management (including a temporary opening of the emergency lanes during peak hours), see the Initiative Staufreies Hessen 2015 ("Congestion-free federal state Hessen"). Consequently, at present, traffic breakdowns occur less frequently on this section. This is bad news for the traffic researchers, but definitely good news for the drivers;-) .

Acknowledgements

We thank the Hessischen Straßen- und Verkehrsverwaltung and the Autobahndirektion Südbayern for providing the historic traffic data.