The Hollywood freeway (the 101 from 134 to the 110) in Los Angeles ranks first in this list.
Anthony Downs, author of Stuck in Traffic has identified four reasons for America’s congestion problem, also applicable to most European and Asian economies: first, most of us work during the same hours of the day; second, the country’s economic success has allowed households to buy multiple cars; third, there are more people now than when most roadways were conceived; fourth, more cars means more accidents which means more delays.
If we take these four issues at face value, then some creative solutions suggest themselves if we really consider traffic to be a problem of significant economic impact:
I leave out telecommuting as that is already an accepted model in many industries, though one could argue it's still underleveraged for certain positions (contained tasks that don't require much coordination or the type of on-the-fly adjustments that face-to-face interactions are so useful for) given improvements in technology. There's probably also still somewhat of a stigma attached to telecommuting that ends up hurting those who do it more than others, if only because the "out of sight, out of mind" ethos still dominates modern corporate value systems.
The traffic problem is a thorny one. On the one hand, increased public transportation seems like something only the government or public institutions can pull off. But the likelihood of some civic solution in a place like LA seems so unlikely that one is tempted to turn towards the free markets and the business world for some economic imperative to make it happen. The truth is probably that some private and public cooperation is necessary to make this work on any large scale, as with commercial flight, and that is daunting.