No. It depends on the efficiency and experience of the driver and the terrain of where the car is driven. If it's hilly to mountainous cruise control doesn't stand a chance over the ability over an experienced driver and how he/she maintains momentum. Cruise control only cares about one thing, the speed you wish to maintain when you set it. Now if there is a super smart new model of car that utilizes camera images, lasers and/or GPS to drive efficiently, well that's a different argument completely.
Okay, account for this: I've been driving for a little over 9 years. I'm on my fifth car. I've had two domestics, one European car, one Japanese car and one Korean car.
The Korean was the most relaxed of all, it wouldn't downshift on inclines and would let the speed go below what I set it at. I hated the car, but the cruise worked like I drove, so as far as I'm concerned, it was good. The two domestics would downshift unnecessarily and accelerate quickly to compensate for the loss of speed, you can imagine that does a number on the FE of a pushrod V6. The German car was constant as **** but not in a pro-fuel efficiency way. It gave better results than most drivers could achieve, though Average FE in the car for me was 8.1. 8.2 with cruise. 8.3-8.5 for the pleb (my family)).
The iM? I've only used it once, it seemed in line with the German.
It *really* depends on the module's programming, but feel free to dismiss my experience.
Oh, I forget, I had an SX4 for about a month (rental) and that one was twitchy, I was better off not using the cruise.
