I just got a new Subaru Outback with their Eyesight Adaptive Cruise Control. I've gotta say it is fantastic and just the sort of fairly simple and safe technology that could ease traffic jams. Certainly outside the city where I live, the way it nicely follows cars at a safe distance seems to make a lot of sense. As soon as the lead car moves away, it neatly accelerates to the preset speed and smoothly decelerates on the engine braking (or even real braking if needed) when it sees the gap closing. It's very obvious on my long commute that probably only 30% of cars seem to be using just regular cruise control, based on how their speed varies on the clear open road.