Tom Vanderbilt write Five myths about traffic in the Washington Post:

1. More roads = less traffic.

This is the granddaddy of all traffic myths, one still held dear by the average driver and certain precincts of state highway offices. More funding for more roads is on the way in Texas, where the governor declared that residents are “tired of being stuck in traffic.” On Memorial Day, it will assume the stature of an intuitive truth: If they just built more roads, we’d be home by now.

But that reasoning doesn’t stand. First, Memorial Day is one of a handful of peak travel days. “You don’t build a church for Easter Sunday,” as the saying goes (a lesson most shopping malls in America have not heeded, judging by their acres of empty parking lots). More broadly, whatever short-term gain that comes with capacity expansion is generally eaten up by longer-term behavioral shifts. As University of Toronto researchers Gilles Duranton and Matthew Turner describe what has been called the “fundamental law” of traffic congestion: “People drive more when the stock of roads in their city increases.”

 Aren’t planners simply keeping up with population growth? Perhaps. Except that growth in vehicle miles traveled has consistently outpaced population growth over the past few decades. And as transportation researcher David Levinson has noted, U.S. roads are already bristling with spare capacity and inefficient use is rampant (such as too-large single-occupant cars all traveling to work at the same time on too-wide lanes). He argues that we should focus time and resources on using the highways we already have more efficiently, rather than on building more.