It's a fairly tightly-targeted radar that picks up the car in front allowing you to set the cruise control and just steer while the car does the braking and acceleration. It's not as clever as a human though because it can't see what's happening ahead of the car in front and anticipate, so you tend to get some fairly heavy braking. During normal driving it also sounds a warning if you're approaching the car in front and haven't started braking, though I haven't yet tested whether it actually emergency brakes or not.