Didn't exactly see that there. Just sounds like they have some money for a road with no specific objective in the first place.
Those details were in the proposal by the toll company CINTRA that the state accepted for this corridor. However it rarely gets reported by the media or the anti-toll groups. The agreement is actually available to the public, but I don't remember where right now. If you search these toll threads from last summer and fall, I posted a link to the agreement back then.
This article is pretty slanted and leaves out much of the pertinent information. Basically this corridor (and the future I-69 corridor) is experiencing big growth, both in population and trade. But the cost of expanding I-35 (and Hwy 59) enough to meet the future growth is far more than to build a parallel road (with connections along the way) that runs through low population areas. It will move a lot of the truck traffic around cities instead of through Dallas, Austin, San Antonio (and Houston.) The same concept as building a loop freeway for traffic to bypass congested downtowns, but on a statewide scale.
A lot of the numbers thrown out ($400 billion, 4000 miles, etc.) are based on a conceptual design of what might be built by 2055. In reality only the I-35 and I-69 corridors (about 1200 miles) and a few short connections will be built within the next 20 years, because those are where the demand will be in the next 2 decades. Bits and pieces might be built elsewhere, for example while a road might not be needed from central to west texas, the electric and pipeline portions of the corridor concept might be built if there is a demand for that. Rather than have as many as a dozen different electric, gas, oil, water, road, rail, etc. corridor strips of right-of-way between 2 areas, the Trans-Texas Corridor concept combines them into a single (albeit wider, but cumulatively much smaller) ROW, so less areas are affected.
Much of what is written here about it is pure bunk. I'd recommend researching both sides.