Everything is bigger in Texas and that includes the roads. There are many differences between Seattle and Dallas when it comes to automotive transportation. In the Northwest people are very passive aggressive and are notorious for driving slow. In Dallas people are prone to hit the gas and drive at speeds that are unsafe for God and man.
Tailgating here is more acceptable and Dallas folk can and will get six inches on your bumper to remind you that your vehicle is traveling at speeds that are unacceptable to them. They often like to play 'let's see how many lane changes I can make within a hundred yards and maybe I'll win a Snickers bar'. Oh and the fine Texans also will use their horn at the drop of a hat.
While traffic can be slow at times it's nothing compared to Seattle, probably due to the fact that there are more highways, service roads, and places to make a U-turn at almost every overpass. They're nothing if not efficient down here and they want to get somewhere with a sense of urgency.
When Dallas natives complain about the traffic I laugh to myself.
"This isn't life in the fast lane, it's life in the oncoming traffic." - Terry Prachett