If you’ve ever found yourself stuck in traffic in your metro area, you might want to print out the chart below, tape it to your wall, and use it for dart practice. It comes via a guest post at the Transportationist by Wes Marshall, and it explains so very much of your earthly woe.

The red line represents vehicle flow along a given road. Traffic steadily rises until someone decides the road needs to be widened. Then the original trend line (dotted red) gets replaced with an even greater travel forecast (dotted orange), as we’d expect by creating more road capacity. But the actual new level of travel developed by this widening (solid red) is even greater than the forecast predicted.

In other words, widening a road invites more cars onto it. That principle, known as “induced demand,” is captured by the grey arrows showing the gap between a travel forecast and an actual travel outcome. Here’s Marshall on the “triple convergence” of induced demand: