Being in the cell industry I have dealt with this problem for years. I make it a priority to ask if someone is calling me from a car... I ask if they are driving in traffic... if so, I tell them to call me back when they have stopped.
By the same token I do the same... if I am driving and cannot pull over, I tell folks I will call them right back.
Just insist that folks that talk to you, "should not be driving" and you are doing your part.