Of course, while this brings up another issue (4-digit Interstates), but what about numbering this I-1080? What would be wrong about numbering this I-180 or I-480, as I believe they don't exist at this time? You could renumber CA-180 to CA-194 (as that number isn't in use, unconstructed or otherwise).
The only time California has ever renumbered 1934-era routes (which Route 180 happens to be) are in the following situations:
- when they conflicted with new Interstate numbers in the 1950s/1960s (i.e. former Route 10 in Inglewood, former Route 5 from SF to Santa Cruz)
- 1964-era Route 69 (former Route 65 which was bypassed by the proposed reroute from Route 198 to Roseville) was renumbered to route 245
Basically, long-standing policy has been, "if the preexisting route is more important in length, then it stays," thus 180 has remained from the very beginning, while urban routes much shorter than the Interstates that used their numbers (5, 8, 10, 15) received new numbers in the 1964 era (35, 26, 42, 7).
Another thing, though unrelated: some of these routes do need to be consolidated, like CA-61 and CA-260, or in the greater LA area, CA-19 and CA-164. It just doesn't seem right to use different numbers for what should be the same route (even Utah has done it with UT-28 and UT-41 in Nephi--it's all UT-28 now).
Both situations are the result of non-completed freeway projects: Route 61 north and south of unsigned 260 and 112 (both of which are signed as 61) which will likely never be constructed, and the short connector between 19 and 605 that is the only unbuilt segment of 164.
As 164 has always been a paper route (which uses the 1934 sign Route 19, which still remains Route 19 in the field), that should honestly have been done away with years ago. If 61's extensions are not to be built, then a redefinition would be useful as well.
(The one instance of where signage for a "virtual" route was adjusted to match has to be Route 242 in Concord, which was built as part of the original Route 24, and was signed as Route 24 between 1964 and 1991 even though legislatively in that time period, it was already 242.)
the best solution is to call it CA-238, especially since it is signed north-south while going almost exactly east-west. The only way that that bannering makes sense is if it is considered the continuation of CA-238, so we may as well unify it under one route identifier.
Since California HAS reused 110 and 105 and 880 (in fact, only waiting one year to reuse 880), I think the best solution would be to give 238 the unused 480 number and leave it at that.
Though part of me wants to be snarky and redesignate 238 as "Truck 580" for laughs (with a concurrency with 880 north of Hayward).