3 ms·

I was under the impression that they use engine breaking, which does not trigger the break lights. https://en.wikipedia.org/wiki/Engine_braking https://en.wiki

• Domenic_S 11y ago
  For normal (non-adaptive) cruise control there are few situations where the brakes would make sense, but one of those is a steep hill. An easy way to find out what happens if you have a decent grade nearby: set a low speed and point yourself down the hill. I commuted over a large grade for some years and all the cars I drove would brake on it. Can't speak for every system ever made, obviously.