Without any obstacles in the road, phantom traffic jams occur when drivers accelerate and brake aggressively.
The Ripple Effect of Bad Driving
August 26, 2010
In the 10-day traffic jam that occurred in China, most vehicles were forced to come to a full stop. While such complete congestion is extremely unpleasant for everybody stuck in it, its dynamics are not complex to understand: if construction reduces the road capacity to below the incoming traffic volume, then a large jam happens.
There are other types of jams that occur in dense, but flowing traffic. These so-called "phantom traffic jams'' can happen without any obstacles on the road. Instead, they are a property of the flow. Traffic models and simulations show that once traffic volume exceeds a critical threshold, small perturbations in the flow amplify, and traffic waves develop. These traffic waves, so called "jamitons," can travel backward along the road, forcing drivers to brake and accelerate constantly.
Our research group, consisting of researchers in the United States, Canada, and Saudi-Arabia, has found that jamitons behave much like detonation waves. Using theories that were originally developed to study explosions, fundamental properties of traffic waves can be explained and predicted.
Unlike true congestion, which in a certain sense are unavoidable, phantom traffic jams are avoidable. The mathematical modeling of traffic allows researchers to not only examine causes, but to study ways to reduce phantom traffic jams. Here are three strategies that could help improve traffic flow:
1) Driving less aggressively and keeping a larger safety distance helps preserve a steady flow of vehicles.
2) Assisted driving devices could, in a subtle fashion, make the driver's braking and acceleration behavior more smooth.
3) Adaptive speed limits along highways can prevent extreme local peaks in traffic volume.