This is probably obvious to older Prius owners but I just realized this recently: In ordinary cars, the cruise control (CC) only has control of the throttle. That is to say, when the car encounters a hill, the CC system increases the throttle. Coming down a hill, the CC unit will reduce throttle. If the speed increases too much, the CC unit can not reduce the speed of the car. On especially steep hills, the speed may well become too high. In contrast in my Prius v, I find that the CC holds the speed study even on steep downgrades. This is possible due to the hybrid system which regenerates power. Even on steep grades, the CC system holds the speed rock steady at the set point. The consequence is that if a conventional car is following you under such conditions, they will suddenly find themselves too close to you. This just happened to me recently on the Palisades Parkway north of NY City. A car that was obviously on CC, came with a few feet of my rear bumper before the drive realized what was happening and braked suddenly. Not a big deal but something to be a bit careful about.
That may be true on gentle East coast terrain. However every time I decend the Sierra Nevada out of Reno ( 7000 Ft. + ) the car accelerates downhill with CC. At that point I regenerate or if the battery is topped up Green I am forced to use Brake Position. Good to hear the Palisades are still there tho. Originally from NYC.
For the following driver. Many vehicles are capable of slowing significantly without showing brake lights. My Jeep is a good example of an old-technology vehicle that slows considerably when you let off the gas, even without down shifting. With down shifting I can make the rear tires chirp from the sudden deceleration. Any experienced driver should know that the car in front may suddenly slow without warning. Unfortunately, many of today's drivers are inexperienced, distracted, entitled, or just don't give a red rats nice person, so they ride your butt and hope for the best, assuming they think enough to hope. Tom
A couple points -- I thought some nonhybrids also used some form of downhill braking with CC. Dad claims his Jeep does this, though I didn't try it to confirm that it really was braking, not simply displaying more engine drag than his previous car. Or automatically downshifting, which previous cars didn't do. Downshifting to maintain speed on downslopes has been common for about a century, so cars that don't increase speed down hills are nothing new. Neither are the inattentive idiotsXXXXXXdrivers who don't notice, except that today we have many more distractions to cause inattention. The distracted driver bumper imprints on the rear of my otherwise clean Prius happened on flat ground, when all vehicles in all four lanes had all their brake lights lit up.
This surprises me a bit since in all the cars I have owned recently, the cruise control system definitely did not cause the automatic transmission to downshift on steep hills to provide engine braking. These cars include a Saturn wagon, Sienna and a Camry. On steeper hills, I would definitely have to touch the break to prevent over speeding.
On a recent trip through the mountains with my 2010 I too was surprised at what it did going down hill to prevent excess speed. Even when in D, it first increased regenerative braking to slow me down and when the battery was full, then it automatically engaged engine braking. Only once the engine was at (noticeably) high revs did my speed start to significantly increase at which point I had to use manual braking. Like some of you, I was suprised at first, but when you think about it, this makes the most sense. I mean, why not control the speed with whatever tools are at hand? As for the car behind being surprised, that has happened to me even with a conventional transmission when I downshifted to maximize engine braking.
For that paragraph, I should have been more clear: downshifting manually on down hills has been common since cars were invented, and remains a standard practice for those of us who still drive stick shifts. Most automatic transmissions can do it too, for those drivers who use more than just the D position. This does not light up the brake lights or otherwise alert the driver behind. So zombie drivers following with traditional non-braking CC cannot claim that a braking-CC is a new hazard. The inattention of the zombie tailgater is the actual hazard here, and that problem existed before any cars had CC.
