The usual Leninist mindset that a revolutionary minority is allowed to break the law and set aside whatever lawfully concluded decisions are made by the elected government.
Having lived in Austin once nearly 40 years ago, and having a spent a few days there recently I agree that the I35 corridor is a monstrous imposition on the city. It was awful then and it's still awful now.
If TxDOt doesn't want to pay the extra cost of lowering the highway and covering it (a good idea to me) then why can't Austin residents pony up the extra cash? Or do they expect the rest of Texas to pay for improvements no other city in Texas gets? Or expect other Texans to pay for improvements that make the congestion for them traveling through Austin even worse?
One thing about liberals, and many other people as well, is that they would rather have somebody else (usually "the rich") pay the taxes, especially if a tax increase is being considered.
If I had my druthers, I would just widen I-35 in Austin to provide the capacity, and then impose tolls to pay for part of the work. The tolls would help with the congestion and the "induced demand." But federal law would prohibit that, except on the new lanes.