There's projects like: https://blog.arduino.cc/2021/06/29/diy-radar-speed-sign-looks-and-works-like-the-real-thing/ https://blog.arduino.cc/2021/06/29/diy-radar

There's projects like: https://blog.arduino.cc/2021/06/29/diy-radar-speed-sign-looks-and-works-like-the-real-thing/ https://blog.arduino.cc/2021/06/29/diy-radar-speed-sign-look... but not sure about the regulations. Not radar, but last year there was a thread from someone who uses a webcam to record trains, and measures speed just through their pixel changes and framerate: https://news.ycombinator.com/item?id=35738987 https://news.ycombinator.com/item?id=35738987 Might work well enough for fixed-route travel... railways especially, but maybe roads are close enough? Probably not as good if the vehicle has more directional freedom and can move diagonally or straight away from the camera. It's less likely to run into any radio licensing issues, though.