Solving Traffic Congestion

April 29, 2012

If a stretch of highway is often congested, we should add another lane to increase capacity. Wrong.

In “The Fundamental Law of Road Congestion: Evidence from U.S. Cities,” researchers show any increased capacity from additional roads is temporary.  Traffic increases to fill the added capacity.  The study’s startling findings include:

  • The number of vehicle-kilometers traveled increases in proportion to the available lane-kilometers of roadways.  If there are more roads, additional drivers start using those roads until congestion returns to the previous level.
  • Increasing the lane-kilometers for one type of road does not significantly reduce congestion on others.  In other words, widening highways doesn’t reduce congestion on city streets.

And perhaps most confounding:

  • Because roadways have natural levels of congestion to which they always return, mass transit projects do not reduce traffic.

So, how should we handle traffic congestion?

The authors conclude that the most effective approach is to charge a fee for cars to travel on roads during peak congestion hours.  This so-called congestion pricing is not yet common but has been applied successfully – and controversially – in major cities around the world. The negative reinforcement encourages people to drive less or to find alternative methods to get to their destinations.

Anyone from London want to chime in?