What do traffic and crowds have in common? I'll give you a hint - they both flow. In fact they flow so much that the same governing principles at play in fluid flow can also be extended to simulate traffic flow and the motion of dense crowds.

Traffic Flow Simulation

Rather than modeling cars as discrete items, i.e., individual cars, in traffic flow simulations cars can be modeled as a continuous variable analogous to density in fluid flow. Further, by assuming that the flow of cars is inviscid (i.e., no damping of movement) it can be shown that congested roads can cause phantom (no obvious cause, such as an accident) traffic jams, analogous to shock waves in fluid flow.

Crowd Flow Simulation

What happens when you get millions of pilgrims showing up to visit Mecca in Saudi Arabia all at the same time? People start to behave as water does when it flows around obstacles. In fact researchers have characterized the movement of dense crowds of people as having properties analogous to:

• Laminar flow - steady, smooth progress of a crowd
• Turbulent flow - stop-start motion of a crowd
• Shock waves - rapid, involuntary movement of people within a crowd

Who knew that fluid mechanics could serve as such a broad foundation to such a diverse range of applications?