If you are about to descend a highway slope signed for "trucks check brakes" or "trucks use low gear", you are in prime territory for B gear. If the descent is less severe, this is the area where some Prius drivers like to use it and others not.

B gear cancels cruise control in the new model Prius, but not in the classic. No one seems to know why the change. Possibly this could explain some of the diversity of opinion about the option.

I may use B gear on more descents than most, in this 2001 Prius with 104k miles. The original brake friction components all appear as new, so I am happy with the decision.

If you use gear in the flats and lift your foot off the accelerator pedal, the car will slow down (relatively) massively. This seems unpleasant, and may interfere with our efforts to float along at high mpg.

DAS