I did a little experiment driving to and from work this week. I drive up a hill 10 miles and down the other side 20 to work. For a few days I drove "accelerator conscious" at 55 to try for the best mileage. Then for the next few days I put the cruise control on at 55 and let it take me up the hill. I got consistently better mileage when I let the Prius feather the gas for me. Has anyone else tried this? All other factors were a constant as far as I can tell.
I've also noted that I get slightly better mileage using cruise than my foot, although I'm closing the gap the more I drive. The one exception is the route from my parent's place to my fiancee's parents' place, which we travel semi-regularly. About an hour and a half of driving, 80km max almost all the way, and up/down/up/down/up/down hills all the way. On that drive, my foot does a better job than cruise, because my foot will allow the car to pick up five or six (or ten or fifteen if I'm not careful...) kmph which help carry us up the other side of the next hill, while the cruise would have to kick the engine in fairly quickly to keep a constant speed after braking all the way down the hill.
The answer for me is - it depends. If I'm in traffic and need to maintain a constant speed, the cruise control is more efficient than I am. However, if I'm all alone on the road and can vary speed by gaining on the downhills and slacking on the uphills, I can beat the cruise.
Likewise, other than times where I need to sustain a steady speed for prolonged time periods I can easily beat the cruise control by allowing speed to vary, gliding down hills, coasting up hills and using 'dead-band' acceleration.
My daily commute is comprised entirely of rolling hills. Constant up and down. This evening, on the only stretch of road with no stoplight for a couple miles, I set the cruise. When flat, the MPG went up; when headed uphill, MPG dropped because Priapus was maintaining speed; when headed downhill, regen braking kicked in to maintain speed again. Normally, I sacrifice a few MPH to ease the load uphill and feather the pedal downhill to eliminate regen braking. My final answer, Regis, it all depends.
the roads around western wa are not flat so its constant ups and downs. i let cruise control take care of it. i use cruise control as much as possible even on surface streets and i get excellent results. i found that left up to me i frequently found myself going much faster than i wanted to. to put it mildly, my Prius rides much nicer than my previous main vehicle.
