Probably what you’re looking for is Systems Theory:
http://en.wikipedia.org/wiki/Systems_theory
But because Systems Theory is interdisciplinary, you could be talking about any number of disciplines. For example, if you tried to use principles of hydrodynamic turbulence to talk about traffic “flow,” you’d probably need to study chaos theory and some sociology. If by “crowd dynamics” you mean a kind of “herd behavior” or “mob mentality,” then you can go the social-philosophic route and read, say, George Simmel or Gustav Le Bon. But if you mean the physical flow of people, again fluid dynamics is probably your best bet (esp. properties of granular fluids).
Does that answer your question, or am I misreading it?