As per Wikipedia http://en.wikipedia.org/wiki/Future_Interstate_Highways (http://en.wikipedia.org/wiki/Future_Interstate_Highways) (I know, I know; you can't always trust it, but nothing's been changed for a while on this page) under Future Interstate Highways:
Proposed routes, extensions and conversions of U.S. interstate highways:
Interstate 21 from Douglas to Willcox in Cochise County, Arizona.
Interstate 23 from Columbus to Deming, New Mexico.
While I click on any of them, it just leads me back to the "Future Interstates" page. Still, if these proposed routes I-21 and I-23 are indeed real, how soon could we expect them to be built?
They, as well as I-19, should simply become spurs of I-10.
someone's gotta be off the deep end here. This is another one that sounds like it should be a three-digit interstate (an x15 given the absence of x05 options)
Quote# Conversion of California State Route 78 to Interstate 18 from Escondido by Interstate 15 to Oceanside to meet Interstate 5.
and this one does not even make any sense:
QuoteConversion of U.S. Highway 83 from Laredo, Texas to connect Interstate 37 to Brownsville, Texas supposedly to be marked Interstate 6 or Interstate 7, but may be viewed as an extension of Interstate 35 from Corpus Christi, Texas.
35 does not go through Corpus Christi - that's 37's southern terminus. If 37 were extended to Brownsville, it would not be the US-83 corridor. 35 and 37 could be extended to Brownsville via the US-83 and US-77 corridors, respectively ... and neither of them had better be numbered I-7!
I have extreme doubts that I-21 and I-23 will ever exist in areas where the numbers fit (though I wonder if the US 20 expressway east of Idaho Falls could become part of a new route up to I-90 at Bozeman, MT). Going from streetview, I don't seen enough to really justify four laning the proposed I-21 and I-23 routes. Maybe if the rules change to allow two lane expressways to be signed as interstates.
And for another Wikipedia error with future interstates:
QuoteConversion of U.S. Highway 71 from Fort Smith, Ark. to Texarkana, supposedly to be marked Interstate 54.
Yea, and it may be off topic (with regards to region), but notice also the N-S Interstate 54 between Fort Smith, AR to Texarkana, TX. It would be a much better extension of I-49.