There's an incidental part that improves traffic with Mexico, but the most important part runs from Evansville, Indiana to Indianapolis.
And it's not a quarter-mile wide. That was just media hype that focused on the part in Texas that would parallel (and absorb) right of way already in place for oil and gas pipelines.
The route East of Dallas was pretty well laid out in the "Big Inch" and "Little Inch" projects. You might enjoy looking up that history. Here's a map:
