This post originally appeared on Orphan Road.

In addition to all the wonderful freedom they provide, cars have two major negative effects on society: pollution and traffic (three if you count the health problems related to auto-centric lifestyles, but that’s still pretty new and second-order compared to the first two). We often conflate the two, but they’re really separate problems.

In fact, one could easily see solving one of them while exacerbating the other. That’s the impression I get reading this article on plug-in hybrids. The more energy efficient our cars become, the cheaper they are to drive. Common sense tells us that people will then drive more, thereby making traffic worse.

This is not to say that energy-efficient cars shouldn’t be welcomed with open arms. It’s just that a good deal of public support for mass transit comes from a combination of the two. If operating a car gets cheaper, there goes one half of the coalition. Thus, it may reduce the demand for transit, while, perversely, making congestion even worse.