For optic flow, you also would have to know the height above the road. That varies with vehicle load, tire pressure, speed bumps, etc. It also would have to wo

For optic flow, you also would have to know the height above the road. That varies with vehicle load, tire pressure, speed bumps, etc. It also would have to work on all kinds of road surfaces, day and night, in rain and snow, with different amount of sunlight, and with varying locations of the sun in the sky. ⇒ I don’t think this is as simple as you make it look.