Another efficiency question from me out of curiosity.
Let's say that I am driving at a decent efficiency rate (say 40 MPG) and am coming up on a hill, with no cars immediately behind me or traffic lights ahead of me. I know that once I crest the hill I will start to accelerate rapidly, building up enough speed going down that I'll eventually need to brake to avoid going above the speed limit.
It makes sense that taking my foot off the gas before I fully crest the hill could help. Decelerate a little as I go up the last tiny bit of the hill, then regain that speed on the way down, avoid having to break soon.
However, this only works to a point. Worst case scenario I allow my car to decelerate going up the hill until I'm going at nearly idling speed, with 70% of the energy output from my idling car going to counteracting gravity on the hill and my overall efficiency being horrible.
So my question is where is the sweet point? How much can one allow a car to decelerate going up a hill before they start to lose more efficiency letting their engine idle to push the car the rest of the way, compared to using gas to overtake the hill sooner despite knowing your have to brake on the way down?