Actually it can be activated at ANY stop. Next time you're at a stoplight try pressing the brake fully to the floor and you'll see "Auto Hold" pop up and can remove your foot entirely. Any press of the accelerator will deactivate the brake and allow you to move.
I go crazy when I drive a car without it. Mercedes introduced it first on the 211 E-Class. I had it on my 2003 AMG E55 Kompressor wagon. It was the first car to have brake-by-wire and actually controlled each brake disc individually with the ESP/ABS sensors so that there was always maximum grip on each tire. It was called Sensotronic Brake and as a side effect, they added the SBC Hold function. It was discontinued after a couple of recalls and it was much more expensive to manufacture as well, three years later or so. I use it every time I stop completely and take my foot of the brake. Then I just press the accelerator to start moving again. I am a lazy bum who does not like to waste calories pressing the brake unnecessarily ! However, I only use cruise control on any car on trips longer than 6 hours for maybe 5 minutes every three or four hours to rest my foot from the accelerator. I like being in full-control, but my foot/leg grows numb after so many hours. These are the contradictions in life, I guess.
It will activate on flat/any terrain if you push the brake pedal down hard enough while at a stop. You should see a small "hold" light come on in the center instrument panel when you do.
Saw Frank's post after I hit reply. His experience is mine. Very convenient.
