I'm not the person you're responding to, but I think this is how what the poster said applies to a SimCity-like model:

>heterogeneity is your guardian angel - varying the path-finding model a little bit from agent to agent hedges against the resonance structures on display here.

Adding a small amount of randomness (occasional 'wrong' turns) reduces congestion on the major paths that would be the dominant route for agents.

>Additionally, you periodically check the accumulated micros against a macro model and correct gross deviations. Neither step is computationally strenuous.

Every once in a while, check and make sure those wrong turns didn't add up to some agents being way far away from their destinations; if so, turn them in the right direction.