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Andras Schmelczer 2026-05-25 21:31:09 +01:00
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src/content/posts/city-simulation-unity-traffic.md
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---
title: A Unity City Simulation for a Cybersecurity Challenge
description: A client-server Unity simulation where REST-controlled traffic lights made mistakes immediately visible through crashes.
title: A Unity City Where Bad PLC Code Made Cars Crash
description: 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.
date: 2026-05-01
projectPeriod: 'July-August 2018'
thumbnail:
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tags: ['simulation', 'systems']
role: Simulation author
stack: ['Unity', 'C#', 'REST API', 'Blender']
outcome: A visual context for a PLC-focused cybersecurity challenge
outcome: Visible consequences for an otherwise abstract PLC challenge
audience: technical
links: []
---
I simulated a city where car crashes were more frequent than usual.
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.
The state of the traffic lights could be changed through a REST API. Drivers followed the instructions of those lights, so if a mistake was made, collisions appeared in the simulation. There was also support for displaying tweets on a HUD.
Three things are worth saying about it:
The project was the context for a cybersecurity challenge about PLCs. Contestants could see the effect of their work immediately, as crashes.
- **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.
The architecture was server-client. Every decision of the agents was calculated server-side, and the real challenge was broadcasting those decisions in a fault-tolerant way on minimal bandwidth.
It was built in Unity with C# as the scripting language. I also made the models and animations in Blender.
There was also a HUD overlay for tweets, which felt clever at the time and dated horribly. Skip that part.