A more sophisticated (but expensive) radar sensor could do the job without the camera. A sensor capable of Doppler processing, sweeping, and tied to some sort

A more sophisticated (but expensive) radar sensor could do the job without the camera. A sensor capable of Doppler processing, sweeping, and tied to some sort of platform telemetry (GPS, INS, etc.) could maintain a large and fairly comprehensive situational picture. Add moving target indication to the signal processing and it could form tracks on all other vehicles on the road, which would provide the motion vectors for them without the need for another sensor. You could even use track behavior to detect anomalies in the road, assuming you have multiple tracks. I could go on all day about this (having actually worked on MTI radar for several years), but I have actual work to do. :P