TomTom's taking traffic congestion to the future, aggregating speed data from its in-car navigation systems to pinpoint precisely which cities have the worst traffic congestion. Here's their scientifically-derived 20 most traffic-clogged cities. The results may surprise some.

TomTom collected data from its Tele Atlas business system GPS data to determine what streets were "congested." In order to qualify a driver has to travel at only 70% or less than the posted speed limits. And while cities like Los Angeles and New York make the top five, it's actually Seattle, Washington at the top of the pile with 43% of the roads considered congested. Full details in the gallery.