Firstly, apologies if this has already been suggested and I've missed it (or if it already exists!).
I'm suggesting that you can operate Waze in a mode whereby it only "receives" data (and works as a GPS) but you don't contribute traffic data. This would be for journeys by bike, motorcycle, foot, taxi, train, helicopter, canal boat, or where you are simply pulled over into a lay-by for coffee and are not actually in a traffic jam.
Entering this mode: either from a pop-up (1. "You have reached your destination: are you actually still travelling by car?" with possibly three options: switch off, non-contributory mode, and continue travelling, 2. "You have been moving slowly for a very long time: are you actually still... and so on) or from a menu option.
Indicating mode: the car on the screen has a red circle round it with a line through it.
Exit this mode: touch the car.
I'm sure there must be some obvious reason I've missed why this doesn't already exist, so feel free to point this out.