If you own a Prius and live in California — particularly freeway-dense Southern California — you’ve gotten a good deal since 2004. A law went into effect then allowing hybrid owners who bought one of a limited supply of yellow “clean air vehicle” decals to drive in the carpool lane, whether or not they were carrying a passenger. But as Felicity Barringer notes in a neat little New York Times piece this morning, the deal is ending on July 1, and decal owners are mad.

It’s easy to see these complaints as whines from over-privileged yuppies, which is how most of the politicians the piece quotes frame it. There’s certainly some of that, but it could be that those over-privileged yuppies have a point. People respond to incentives, and getting to drive in the carpool lane is at least something of one. As UCLA economics professor Matthew Kahn says in the article, California hybrid owners are “a mixture of people wanting to signal their virtuousness and people wanting to get to work quickly.” If the decals spurred people in the latter category to buy hybrids who wouldn’t have otherwise, then they’re doing something right.

Obviously, small initiatives like this aren’t going to make a big dent in U.S. carbon emissions, but in the absence of major federal movement on cap and trade or another carbon pricing program, tiny things like hybrid decals are what we’ve got. At the very least, the state government in California ought to commission a study to figure out if the decals actually increased hybrid sales. If they did, why not keeping the program going? They could even throw out the cap on decals this time. That could make carpool lanes more crowded, but if it does, that would only mean it’s worked at putting more hybrids on the road. 

Dylan Matthews is a student at Harvard and a researcher at The Washington Post.