"What causes congestion? In a word, 'you.' Most of the Mojave Desert is not congested," wrote report authors David Schrank, associate research scientist, and Tim Lomax, research engineer.

In the last 20 years, travel has increased by 105 percent in metropolitan areas but road capacity -- measured by freeways and major thoroughfares -- has only risen 45 percent.

Solving the problem not only includes focusing on "critical" corridors and easing choke points but making work schedules more flexible and building more areas where people can walk to work, the study said.