AR speedometer

Imagine this: You're living in a town with many kids. Adults like to drive cars. Fast.

What if you were able to estimate their speed with your smartphone?

I mean, we have AI (in this case, image recognition) and AR already. The devices are powerful enough to run them (given a certain price). Browsers can understand WebXR.

I wonder, whether we could pull this off: Use rear camera to see the street. Apply image recognition to detect cars. Use some heuristic to estimate their size. Use some heuristic to estimate their distance (optical size and zoom?). Display feedback (distance, speed, time until arrival) via AR on the screen.