Most adaptive cruise systems use radar or lasers to track the position of vehicles ahead. A few use gyros and steering angle to figure out where the road's going; however, Nissan's next generation Intelligent Cruise Control looks much further down the road.
By taping into the vehicle's GPS system, Intelligent Cruise can analyze the road ahead and adjust your set speed accordingly. For example, if the system sees a curvy section ahead, it may reduce your speed to compensate. This system should be included in the next-generation Nissan Fuga in the Japanese market--and hopefully the Infiniti M in the U.S. market.
Future systems could also tie into weather and traffic systems to compensate for slippery conditions, prebraking for traffic, or slowing for construction zones.