The other important thing about I-35 in Austin is being prepared by being in the correct lane when the road splits into the
upper and
lower decks. For some insane reason, the
left 2 lanes of the road lead into the lower deck, with all the local exits through the middle of the city and
downtown, while the
right 2 lanes form the
express lanes of the upper deck, next exit just before the two sides merge back together again. If you're hugging the right-hand lane waiting for your exit, and it happens to be just after this split, you're going to miss your exit by a long way!
In any case, both sides of the road are this way, so you should quickly learn to get into the 2nd lane from the left when headed for a mid-town exit and starting from outside the 2-level region.