Then, have TxDOT et al abandoned efforts to include US 281 "from the Rio Grande River" to US 83/I-2 as part of I-69C?
Well, technically US 281 starts in Brownsville near the Rio Grande River. You could make the argument that I-69E to I-2 fulfills that requirement even if it's not signed as I-69C along there.
At its November 16, 2012 meeting,
the AASHTO Special Committee on U.S. Route Numbering disapproved TxDOT's request for an interstate designation for US 83, in part because TxDOT had not specified a number for the designation (page 1/7 of pdf). In looking at the
Texas Transportation Commission September 27, 2012 Minutes, I'm beginning to wonder if Texas did not specify a number because they may have thought that the federal legislation did not give them a choice in the matter (pp. 29-30/34 of pdf):
This minute order authorizes the department to petition the AASHTO Special Committee on US Route Numbering to recognize one or more segments of US 83 as logical additions to the Interstate System, with the condition that FHWA finds that each segment meets the criteria contained in Appendix A to Subpart A of 23 CFR Part 470 and approves the addition to the Interstate System. It is further recognized that it is the purview of the AASHTO Special Committee on US Route Numbering to assign an Interstate route number to the designated highway in coordination with FHWA.
IT IS THEREFORE ORDERED by the Texas Transportation Commission (commission) that the department is authorized to submit an application to the AASHTO Special Committee on US Route Numbering requesting the recognition of one or more segments of US 83 in the Rio Grande Valley as logical additions to the Interstate System.
IT IS UNDERSTOOD that following approval by the AASHTO Special Committee on US Route Numbering and FHWA, the commission will designate the segments with the assigned Interstate route number by minute order.
I wonder if Texas officials were concerned that, since the US 83 routing between US 281 and US 77 (plus US 77 to the border) is basically a substitute for US 281 from US 83 to near the border, a strict reading of the statute would have required US 83 between US 281 and US 77 to be designated as I-69C and would have also required the US 83 segment from US 281 westward to have been assigned another interstate designation? Such a concern would explain the language "one or more segments of US 83". It would also explain the language that "it is the purview" of AASHTO to "assign an Interstate route number". In short, Texas may have been telling FHWA/AASHTO: "You tell
us what the statute requires".
I assume that, once AASHTO kicked it backed to TxDOT, TxDOT took it as a green light to go for I-2 for the entire US 83 segment at the May, 2013 AASHTO meeting. Maybe one day the "inside story" will be revealed as to why Texas did not initially request a specific interstate number for US 83.