In 1975 TX and NM asked AASHTO to assign a new US highway designation between Dallas and Elida NM; following is the route description from the actual minutes of the meeting:
(Note: when making that map I did not take the time to research which bypasses had been built by 1975 and which had not. I know that the Guthrie bypass had not been built, but the through-town route that existed in 1975 is no longer open to traffic.)
The proposal was rejected by AASHTO's US Route Numbering Committee. I suspect one of the main reasons was because it included a 160-mile redundancy with US 82. In response, a few years later (in about 1978) both Texas and New Mexico changed their dual-state highway designation between Lubbock and Elida from 116 to 114. So then the SH 114 designation extended all the way from Dallas to Elida, accomplishing essentially the same thing as a single US route designation would have.
But if AASHTO had accepted the proposal, what would have been a good number to assign to this new US route? Today the east end of US 80 is in Dallas, so one immediate thought might be that this route could have easily become an extension of US 80. However, at the time of the proposal, US 80 still extended far to the west of Dallas. So what number would you have given this route? Leave your ideas in the comments below.