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Comment by layoutIfNeeded | Hacker News Reader

That's definitely not how it works. Traffic is a nonlinear dynamical system with all sorts of non-intuitive coupling between various components.

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What's the difference between a dynamic system and a dynamical system?

A dynamical system (https://en.wikipedia.org/wiki/Dynamical_system) is basically a bunch of (continuous / discrete) variables whose evolution is governed by a set of (differential / difference) equations. E.g. a pendulum is a dynamical system whose state can be described with a single variable 𝜃 (the angle of the pendulum), governed by the differential equation:

𝘥²𝜃/𝘥t² + g/l sin(𝜃) = 0

(where g is the gravitational acceleration and l is the length of the pendulum)

Dynamical systems whose behaviour is linear are kinda well-behaving and easy to analyse. (linear in this context means that the system's response to a linear combination of inputs will be the same as the linear combination of its responses to the individual inputs) Non-linear systems on the other hand behave chaotically, producing wildly different responses to slight differences in their inputs.

I'm not sure what a "dynamic system" is though.

In some cases that’s exactly how it works. There’s a four way stop on a major commuter route where I live. Most of the traffic passes through it in a straight line and there is a major build up, like 20-30 min long during rush hour. In one direction there is a side road that loops around off the main road for about 2 miles in a big U and joins back up again at that 4-way stop. Before Waze became popular you could shoot around this bypass and be the only car on that side of the stop sign. Now there is a pretty significant amount of traffic there every rush hour thanks to the GPS apps. Lowell road and Barnes Hill road in Concord, MA for anyone curious.

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