© Charles Chandler

 

Traffic on the highway proceeds at a normal rate, until the number of cars exceeds a certain threshold. Then the speed drops by 50%. At the slower speed, fewer cars get to their destinations in the same period of time. So even more cars get packed onto the highway, which further decreases the speed. And this, of course, is what causes traffic jams.

 

The cost of traffic jams is measured in lost time for commuters, increased pollution from the vehicles operating inefficiently in stop-and-go traffic, and in a higher incidence of accidents. The quick solution is to build more highways, bridges, and tunnels. But such projects are extremely expensive, and during construction (which can take years), the problem gets worse before it gets better.