Decade after decade, American metropolitan areas continue to widen their highways in order to reduce congestion. And decade after decade, congestion just keeps getting worse. That may be counterintuitive, but it’s because of a phenomenon called induced demand. This simple gif illustrates how it works:

Of course, it’s a little more complicated than this gif. Congestion keeps increasing not only because more people drive, but also because more people drive farther. And because the more highways we build, the less walkable and transit-accessible our cities usually become. And because the more desperate our congestion situation becomes, the more some groups attack using money for anything other than more highway widenings.

Highway congestion is a negative feedback loop. The only way to really solve it, besides economic calamity, is to break out of the loop by attacking its root causes. Rather than applying highway-widening band-aids that only work for a few years, build urban communities with multimodal infrastructure, in which it’s just as convenient (or more so!) for most residents to get around without a car than with one.

That doesn’t mean no new roads are ever needed. New communities and densifying ones need streets, after all. But it does mean we should be skeptical of plans to make highways bigger. In the long term, that money is usually better spent elsewhere.

 Comment on this at the version cross-posted to Greater Greater Washington.