The black hole of traffic

Analog models use simpler, well-understood systems to represent more mysterious phenomena. Various analogs for black holes have been found in Bose-Einstein condensates, shallow water waves, and slow light. de Souza and Matsas discovered another black hole analog: vehicular traffic.

A black hole is a region where information cannot escape. Car brake lights carry information, indicating to cars behind them that they should also brake. If cars are moving to the left on a straight highway, these taillight flashes propagate to the right.

If weather impairs visibility, however, the drivers’ reactions may be delayed until after they move to the left of the first vehicle that braked. This means the taillight flashes propagate left instead of right. In addition to potentially causing accidents, the authors realized the poor visibility traps information in a small region, forming a traffic black hole.

To understand how certain weather conditions lead to traffic black holes, they developed a causal diagram corresponding to the analog model. Their work revealed that accidents could be avoided if risky areas are assessed before poor weather to determine where the frontier of the traffic black hole would form. Then drivers could be warned to slow down before reaching this event horizon.

“It is possible that this simple physical-informational approach, complemented by more traditional ones, could help to avoid traffic accidents under impaired visibility conditions,” author George Matsas said. “We would be delighted if our paper helps to save lives in the real world.”

But to make this model more applicable to real traffic, traffic dynamics experts first must collect real-world data.

Source: “Black-hole analog in vehicular traffic,” by Luanna K. de Souza and George E. A. Matsas, American Journal of Physics (2022). The article can be accessed at https://doi.org/10.1119/5.0091957 .