“The radar creates a doppler map, and recognizes not only the vehicle, but how far away it is and how quicky it’s approaching. It communicates this to the cyclist by a system of LEDs, and to the car by increasing the rate at which the tail light blinks as the car gets closer.”
Source: makezine.com
While the application described here is for use on a bicycle, it shows that radar technology has become compact enough, serving information in a sufficiently distilled form, to be useful in robotics.