On my trips using speed control on freeway hills, I notice that the car tends to lose a few miles per hour then noticeably increases engine speed to bring the car back up to speed. when I control it, I slowly add more gas to keep the speed constant. Which would use more fuel - letting speed go down a bit then speeding back up or keeping a steadily increasing foot on the pedal? I would have thought the former was worse but it seemed in my testing that the pressure on the pedal gave me worse mileage. My tests were based on a few hours of driving and watching the numbers on the Trip Info display.

 

At freeway speeds I find I get the best mileage on cruise control. When going downhill I try to do "pulse and glide" but I don't know that it really improves my mileage. I probably would do just as well to stay on cruise control.

 

I use the cruise control a lot. Even in town but this is on level main streets and highways. Where it's slightly hilly I find holding the accelerator steady works best.

On a rather rough road, the cruise control only gives the engine just enough throttle to keep the car at a steady speed and helps save gas.

I found with the TCH when you have to drive slow. You can use your cruise control starting as slow as 25/26 miles per hour. This is best when in the EV Mode.

 

On interstate trips when traffic is light, cruise control is my preferred method.
Heavy traffic and/or mountains, I use the accellerator pedal.

 

It's a really simple matter to over-ride the CC by depressing the gas pedal slightly enough to overcome the incline that you see upcoming but the CC cannot.

On a standard car I often disable OD just upon reaching the incline.

 

My interstate driving is a mixed bag, consisting of some flat-land areas, and other sections consisting of gentle rolling hills. I find that in the flats, using the CC and letting the ECU work out the best solution works best. In the hills, I can do better. On the downgrades, I gradually build speed, while holding a target mpg on the consumption gauge (typically somewhere between 40-50 mpgs. On the upslope, assuming I'm not obstructing following traffic, I'll set a target mpg, typically 15 or 20, and just let the speed bleed off gently, until I reach the minimum speed I deem safe for the conditions (usually I won't let it decay below 55 mph).

 

Ditto for me rburt07.

 

I've heard the idea presented that the faster you get back up to cruise speed (within reason--opening the throttle 100% would be silly, for example)the better economy you get, since you spend less time accelerating.

If that turns out true then it would explain why the speed control works how it does.

That said, hilly terrain confuses the hell out of it. The "open throttle hard to get back up to speed" kicking in when you're just starting up a grade results in the engine revving hard to try to accel. up a slope, that can't be good for your economy. Perhaps a niche example but if you live in that kind of area it makes it hard to use the speed control off the main roads.

 

Just got back from a trip to Reno and discovered the same thing rburt07 said. While going through towns at 25 and 35 miles per hour, the cruise control still works at those speeds. What’s more, it kept the car in EV mode! Keeps me from getting a ticket and saves gas!

BTW, Los Angeles area to Reno, I got 39 MPG going (~3700 foot elevation gain) and 43 MPG coming back. Friends were amazed that we went all the way there, plus drove around for awhile before finally getting gas.

 

I use cruise control all the time and it does help keep the speed constant. Other than very hilly and curvy roads I use it when ever I can that is safe. I seem to average between 39-43mpg for all of my driving. Even at speeds of 35 it still works great!