[hcarvalhoalves]

> Closing roads can improve everyone’s commute time.

SimCity is a great way of showing this effect interactively.

In the simulation, citizens always take the shortest path (individuals try to maximize individual gain), but if you connect your entire city like a grid they avoid high-speed roads, deadlocking the traffic (worst game outcome). If you adopt a city plan full of cul-de-sacs and connect it with high-speed roads like a tree the traffic flows better (best game outcome), even though there are less roads and the individual's commutes are longer.

SimCity is an interesting game to explore the concept of game theory since you don't participate as an actor but rather as the rule maker. It shows how you have to adopt counter-intuitive solutions from an actor viewpoint to enforce the desired outcome (backtracking). Once the conditions are met the simulation converges to what you desire.

[YokoZar]

Doesn't some of this behavior come from the rather preposterous way simcity models its drivers? A model where there is no persistent data and the heuristic is instead "go to nearest house and declare that home, if someone beat me there go to the next nearest house" naturally lends itself to a tree model, as no one actually wants to go anywhere but the next link in the chain!

A more reasonable model (and why gridded streets work in the real world) would have people who desire to go to different places in the grid.

[hcarvalhoalves]

SimCity 4 "Rush Hour" introduces a refined traffic simulation where you can inspect the commute of each citizen and it's exactly what you would expect in real life - they go to anywhere in the city, not only nearby.

Grid layouts don't optimize for heavy traffic [1] because drivers choose shorter paths, making it worse for all [2]. In real life you don't have grid layouts without large roads, one-way streets, overpasses and other ways to improve flow.

A tree layout avoids this by directing through traffic to higher-capacity roads without intersections [3]. The downside is that individual commutes get longer. It's just one possible solution, but an interesting one because it improves traffic (removes the Prisioner's dillema) by closing roads (denying options to the game actors).

[1] http://en.wikipedia.org/wiki/Grid_plan#Late_19th_century_to_...

[2] http://en.wikipedia.org/wiki/Prisoner's_dilemma

[3] http://en.wikipedia.org/wiki/Street_hierarchy

[YokoZar]

Thanks, this is all very interesting. I do think there's a bit more to consider though, such as how it's much harder to design walkably compact neighborhoods with arterial roadways than with gridded ones, meaning you might just get fewer cars in the gridded setup.

[hcarvalhoalves]

Yes, it's about trade-offs. The point I was making though is how the simulation models the counter-intuitive concept of "closing roads improve traffic" because the simulation embodies a property of game theory that also applies in real life.

[anon4]

On the other hand, once you can factor road utilisation in your personal preference function, you can take the slightly longer but much less used road, meaning that for certain actors a sub-optimal road grid is better than a tree.