I don't work on these radar systems, but have played a lot with ultrasound for robotics. It seems possible these radar systems give almost continuous false pos

I don't work on these radar systems, but have played a lot with ultrasound for robotics. It seems possible these radar systems give almost continuous false positives. You could get a pretty strong return from potholes, slightly sunken drain covers, etc. Using doppler to reject any return that matches the car's own road speed just leaves the returns from moving vehicles. You can then track speed vs distance to sanitize that data. It becomes a tractable problem then to detect that the car in front is slowing quicker than you are. But telling the difference between a stationary car and a slightly misaligned bridge expansion joint is probably not trivial.