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The rates of traffic flow on different kinds of 4-way intersections

posted by Jason Kottke   Dec 18, 2017

This is an animation of traffic flows simulated on 30 different kinds of four-way junctions, from two roads intersecting with no traffic lights or signs to complex stacked interchanges that feature very few interactions between individual cars. It was recorded in a game called Cities: Skylines, a more realistic take on SimCity.

The developer’s goal was to create a game engine capable of simulating the daily routines of nearly a million unique citizens, while presenting this to the player in a simple way, allowing the player to easily understand various problems in their city’s design. This includes realistic traffic congestion, and the effects of congestion on city services and districts.

I don’t know how accurate the observed rates of flow are — where my transportation engineers at? — but it’s super interesting to watch the various patterns get increasingly complex and efficient, and how the addition of dedicated turn lanes, roundabouts, overpasses, and slip lanes affect the flow. Be on the lookout for the turbo roundabout, the diverging windmill (which, coincidentally, is the name of my signature dance move), and the incredibly complex pinavia,1 which can handle almost five times the traffic flow compared to a simple intersection with no lights.

  1. The pinavia interchange is apparently patented, which is a fascinating thing in its own right.