You are absolutely correct. There indeed are several planned; and included within those plans are rails, between them:
News coming on the NAFTA Rail road along the super-corridor
Second pic above is screen shot of first page and link to pdf file.
Captions for photos:1. The Port of Lazaro Cardenas on Mexicos Pacific Coast is in the midst of a $290 million
expansion that will expand its capacity to more than 2 million TEUs per year.
2. The worlds three largest shipping companies already offer regularly scheduled service at Lazaro Cardenas.
3. In 1997, Kansas City Southern and TMM joined forces to create Transportacion Ferroviaria Mexicana (TFM), paving the way for what is now known as The Nafta Railway.
4. A single 1,300-mile railroad, under common management, seamlessly connects Mexican seaports to the central United States.
5. This is the sole railroad bridge connecting the United States with Mexico at Laredo, Texas.
Where can I find that super-corridor map you posted?