---
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:
  src: ./_assets/city-simulation.jpg
  alt: Screenshot of a Unity traffic simulation.
tags: ['simulation', 'systems']
role: Simulation author
stack: ['Unity', 'C#', 'REST API', 'Blender']
outcome: Visible consequences for an otherwise abstract PLC challenge
audience: technical
links: []
---

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.