A tax on plastic bags doesn't seem to do much to deter their use, at least in Washington. Photographer: David Paul Morris/Bloomberg
A tax on plastic bags doesn't seem to do much to deter their use, at least in Washington. Photographer: David Paul Morris/Bloomberg

A few years back, Washington passed a tax on plastic bags. The Anacostia River apparently had a lot of plastic bags floating around in it, and the District of Columbia hoped that the bag tax would cut down on this highly negative externality. The result, in my experience, was some grumbling from dog owners, and then . . . not much else. I shop too irregularly, often on the way home from the office or some other appointment, to reliably carry cloth bags. And the bag tax adds somewhere between 20 to 40 cents to a $150 grocery bill. I try to be frugal, but even I am not going to carry reusable bags in my briefcase for the off chance of saving 40 cents.

However, the government reported that it was a rousing success; a survey they commissioned showed that the tax had cut usage by more than 50 percent:

The polling commissioned by the environmental agency and conducted by the research firm OpinionWorks reached 600 city residents and 177 businesses. About two-thirds of respondents said they had noticed fewer plastic bags littering the city since the tax went into effect. Residents estimated they used significantly fewer disposable bags -- an average of four a week today, compared with 10 a week pre-tax -- and businesses reported providing significantly fewer bags to customers.

Which leaves just one question: Why is the revenue from the plastic bag tax still rising?

In between the District’s 2012 and 2013 fiscal years, bag tax revenue grew by about $12,000 — a half-percentage point rise that represents well over 200,000 additional bags.

When the Washington Post's Mike DeBonis put that question to officials, they offered the officialese version of staring at your shoes and mumbling. The population had grown, they pointed out, and they’d increased outreach with businesses that collect the tax. None of which could possibly be enough to offset a 60 percent decline in plastic bag usage.

The more plausible explanation is simply that people aren’t very good at remembering what they used to do. For that matter, they’re not particularly good at telling you what they’re doing right now. If you ask folks if they’ve responded to the new bag tax by using fewer bags, they’re going to be tempted to lie and say that yes, of course they have -- or just to err on the side of lower numbers when they’re asked exactly how many. And even if that weren’t a problem, how many people have an accurate count of exactly how many plastic bags they used in the last week? What about that time you stopped in the drugstore for a new lipstick? Did you count the Chinese food delivery you ordered on Wednesday?

On the other hand, tax collections are much more likely to be consistent. I don’t say they’re an accurate gauge of how many bags we’re using; I’m sure some businesses cheat and don’t collect the tax, and I’m sure some folks at the self-checkout cheat and don’t pay it. But if we’re collecting more bag taxes than we used to, it’s a pretty good bet that we’re using more plastic bags.

That doesn’t necessarily make the bag tax a bad idea; the funds it collects are used to clean plastic bags out of the Anacostia River, and there are solid economic policy reasons to try to make the folks who cause the externality pay the costs of abating it. But it doesn’t seem to be doing much to abate the use of plastic bags, no matter what they say on the phone.