Tax just makes things more expensive, and is very slow to elicit change.
Taxing plastic bags while grocery shopping just makes your groceries a tiny bit more expensive. If you ban plastic shopping bags altogether they disappear overnight.
update: I agree that trying to define "single-use" is difficult, instead I think governments should just choose an item that has good alternatives and ban them.
My country banned single use supermarket bags, which they defined by the thickness of the material and whether they had cut-out handles. So a supermarket that used to charge 10c for one of those bags replaced them with 20c bags of slightly thicker plastic with attached handles. For me, the extra cost was negligible so I just bought the more expensive bags and threw them in the rubbish. They don't offer them anymore, for some reason.
Here in Australia the thin bags were free and people used to use _a lot_ of them. Now they sell bags that are thicker and re-usable, but a lot of people bring their own bags.
I read a study that suggested the total plastic usage has gone down, but not by as much as you would think.
I though they weren't banned for their amount of plastic usage, which was surely negligible compared to the packaging of the products people put in them, but for their tendency to blow away and end up in the environment. Thicker bags might not be so easily blown away so maybe it's OK if we all use them? I don't know really because nobody actually analyses this stuff - the decisions are made in response to public outrage.
Taxing plastic bags while grocery shopping just makes your groceries a tiny bit more expensive. If you ban plastic shopping bags altogether they disappear overnight.
update: I agree that trying to define "single-use" is difficult, instead I think governments should just choose an item that has good alternatives and ban them.