Pedestrian Dynamics

The blue colored boids want to go right. The red colored boids want to go left. All boids want to avoid collisions. These simple rules and interactions can give rise to lane formation and phantom traffic jams, as showcased by this simulation.


Blue flow:
Red flow:


Rightward bias: Speed variance:

Phenomena

  1. Lane formation: Eventually, the boids will forms lanes such that all boids in the same lane are travelling in the same direction. Lane formation happens because boids keep steering away from boids coming in the opposite direction, until they reach a state wherein they no longer encounter opposing boids (that is, in a lane). A critical number of boids is required for lane formation, below which there is just not enough interaction to faciliate lane formation. The size of the "privacy zone" also plays a role here. The number of lanes possible depends on the width of the pathway. If there is a bias in direction, then the minority boids may take longer to form their own lanes. A high variance in walking speed impedes the formation of lanes, as described in the next point.

  2. Phantom traffic jams: A congestion is called a phantom traffic jam if there was no long-term inertial cause (example: vehicle break down, obstacles on road, etc) behind it. They typically happen because vehicles decelerates too much (to take a turn, to avoid coming too close to the front vehicle, etc), which causes the vehicle behind it to decelerate, and so on. This causes a "shockwave" of deceleration to travel backwards and is resolved only when the last car in the chain can safely chose not to decelerate. In this simulation, phantom traffic jams are caused when there is high variance in speed. The faster boids will have to decelerate and turn in order to get ahead of the slower boids, and this obstructs the movement of the surrounding boids. This also obstructs formation of lanes. In real-life, however, phantom traffic jams are mostly associated with vehicles (not pedestrians) and they happen in laned roads/highways.


Note:
  1. The model in this simulation is inspired from this paper.
  2. The boundary condition is periodic. However, interactions don't happen across the boundary. This is to simulate the effect of entering a new road.
  3. If all boids are moving in same direction, and if variance is maximized, then flow decreases. This effect is more pronounced at higher densities. This observation has been vaguely connected to phantom traffic jams.
  4. Boids also steer away from the boundaries
  5. This simulation may lag on lower end devices
  6. Related: Collective Behaviour, Vicsek Model

Developed by ChanRT | Fork me at GitHub