When I ride to work I get on Mopac at Convict Hill (carry my bike over the fence) and take Mopac to Barton Skyway where I work. For most of that distance I'm on the frontage road and it's reasonable, but over the greenbelt there's no alternative to taking the lane. Problem is, it's a 65 mph zone, the lane I take is a turn lane (so there's merging traffic), no shoulder, a barrier with a significant drop on the other side, it's a 3 degree downhill (so you're doing about 35 mph, which is good but it increases the pucker factor) and the bridge shakes to really unnerve you

I can take other roads to Lamar and 360, but then I'm taking 360 to Mopac, and that's not much better and still a few miles longer. The safe route is to go over to Manchaca or so and take the small roads to the east of Lamar up to Barton Springs and then take it to Mopac and go south to my work -- but that doubles the length of the commute.

But yeah, if you live near downtown, it's easy to be car free.