schmelczer-dev/src/content/posts/city-simulation-unity-traffic.md
2026-05-26 08:28:37 +01:00

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title description date projectPeriod thumbnail tags role stack outcome audience links
A Unity City Where Bad PLC Code Made Cars Crash A REST-controlled traffic-light sim for a cybersecurity event. Bad PLC code showed up as car crashes, the most honest feedback loop I've shipped. 2026-05-01 July-August 2018
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./_assets/city-simulation.jpg Screenshot of a Unity traffic simulation.
simulation
systems
Simulation author
Unity
C#
REST API
Blender
Visible consequences for an otherwise abstract PLC challenge technical

A small city in Unity where the traffic lights were driven by a REST API. Contestants in a PLC cybersecurity event would write control logic; bad logic made cars crash, and they'd watch it happen.

Three things are worth saying about it:

  • Visual feedback was the whole point. Most security challenges punish wrong answers with a red "incorrect." This one punished them with car wrecks, and people learned faster.
  • Server-client, all decisions on the server. Every agent's behaviour was computed centrally and broadcast. The harder problem wasn't simulation; it was getting the broadcast to be fault-tolerant on the conference Wi-Fi without flooding it.
  • Built it solo, including the models and animations in Blender. Not a flex, just context for why everything's a little janky.

There was also a HUD overlay for tweets, which felt clever at the time and dated horribly. Skip that part.