When the city council in Austin, Texas, passed a single-use plastic shopping bag ban in 2013, it assumed environmental benefits would follow. The calculation was reasonable enough: Fewer single-use bags in circulation would mean less waste at city landfills.

Two years later, an assessment commissioned by the city finds that the ban is having an unintended effect –- people are now throwing away heavy-duty reusable plastic bags at an unprecedented rate. The city's good intentions have proven all too vulnerable to the laws of supply and demand.

What's true for Austin is likely true elsewhere. Plastic bag bans are one of America's most popular environmental measures of recent years . . . .

plastic bags simply aren't that big of a problem. . . . . A more finely tuned litter survey in Fort Worth, Texas (reported in the Austin assessment) found that just 0.12 percent of the weight of litter in the city (which does not have a ban) comes from single-use bags.

Nonetheless, . . . weight isn't the only measure of environmental impact. Single-use plastic bags pose outsized problems in the form of visual pollution on the landscape . . . .

reducing the use of a product that's harmful to the environment is no guarantee of a positive environmental outcome. . . . To that end, the city encouraged residents to instead use reusable bags. Those bags have larger carbon footprints, due to the greater energy required to produce their stronger plastics, but the city figured the overall impact would be lower, as consumers got acquainted with the new, more durable product. What the city didn't foresee is that residents would start treating reusable bags like single-use bags. . . .