I live in France, and in my region plastic bags have become "illegal". Stores provide heavy-duty re-usable bags for purchase (at a minimal cost - and the stores replace them free of charge) or bags which are biodegradable. Everyone keeps bags in their (tiny, fuel efficient) cars and carries them into the store when they go to shop. The change was painless - I never heard anyone complain. And like many changes-for-the-better, everyone wonders why we didn't do it sooner... Indeed, the reusable bags are sturdy, carry more, never break - and when the bags are full the handles don't cut into your hands like the plastic ones do ... It seems all one needed to do to "motivate human behavioral change" in this case was to take the plastic bags away!