I'll guess, I'll guess, Question 1: EPA (actually court upheld that in most cases a cost benefit analysis is not necessary in setting health based air quality standards - wish I had a reference at hand). If Texas chooses to implement CO2 reductions within the bounds of it's legal framework it has every right to without the Senate approving the Kyoto protocol.
Question 2: EPA, and other federal agencies. The big question is how much federal highway money does Texas collect, and what would happen without it?
While GHG emissions and "global warming" are generally a different subject than ozone non-attainment requirements (federal), the fact of the matter is that pretty much anyone has the opportunity to petition executive branch agencies for action. Whether or not the agencies take that action likely depends on the general political atmosphere and specifically the political clout of the petitioning group.
"What would happen without the Federal Highway Money? Around here 80% is going for mass transit. We did get a new bridge and some piddling money to improve a couple of interchanges. Nothing that will reduce congestion. Or emissions