I don't understand why Chicago could build elevated light rail in 1893 and Austin isn't considering it now. There are lots of possible ways to build such a system that instead of slowing down traffic at grade would add value to the entire city.
Disney World has been running a commercial monorail for decades. This can't possible be difficult.
Although of course cost is a serious matter I think the light rail expansion proposed was not attractive for other reasons besides cost. The existing Metro line causes at least as many traffic problems as it solves. We don't need more like that.
We could also elevate bike lanes, sometimes on the same structure.
Why aren't we thinking about the third dimension? It baffles me.