There's been a rumor bouncing around Texas for years, that
the Highway dep't is mostly staffed by Texas A&M Grads, and they decided to have some fun with Austin's freeways, while the little town of College Station got really well designed roads.
I tend not to believe it, because Dallas, Houston, and San Antonio also have lots of traffic problems. It's really a growth thing, and it would be horrifically expensive to widen a freeway through downtown Austin. Plus UT Austin has ~52k students near downtown, which makes for an epic rush hour.
And yes, take the 130 Toll Road to avoid downtown Austin, every chance you get. Avoid downtown Houston, too!