A list of the US cities with the worst highway bottlenecks. High traffic highways in the United States are concentrated most highly in these areas. There are many causes of traffic congestion, and these cities probably have them all. List of high traffic bottleneck areas in the US is sorted by worst bottlenecks to the relative best, but list can be sorted by any column. Source: American Highway Users Alliance, Unclogging America's Arteries, 1999-2004.