Biz-80 also amounted to a lot of confusion in giving directions. Imagine if you are west of Sacramento (like in Davis) and need to give directions to the Arden Fair Mall. You'd say take I-80 east and then at the 80 split interchange don't take the blue 80 to Reno, instead follow green 80/US-50 to Sacramento through town and then at the Oak Park interchange take green 80 to Reno and get off at Arden Way. These were confusing directions that I heard when I lived in the area.
In the 1964 renumbering, CA was very big that only one number should be used for one road to ease travel confusion. It seems odd that with such a mindset, it would be appropriate to have two separate roads in the same city both using the same number <80>, with one using the red/blue and other using green. Nowhere else does this exist in CA, where the highway numbering is very strict that once a number is used, it cannot be used elsewhere in the state.* Its confusing and IMO, it would be better to get rid of this second 80 freeway and renumber it as US 50 along the EW portion and CA 51 as the NS portion.
Now, in NC, having an I-40 and a green-40 freeway is/was normal. But that's not normal for CA.
I agree with you, it is confusing to have two I-80s in the same city and I agree with your suggestion. The only thing I'd add is that the 1964 renumbering was all about reducing duplexes and confusing multiple routes, but making old I-80 into I-80 Business was a 1980 decision so it was a new generation of engineers.
Heh. Syracuse is going to have two I-81s in a few years.
Unless they simply sign the southern "stub" as I-181 or the like, and the section north or I-690 to the current northern I-81/481 junction as the rerouted I-481 (to correspond with the existing NY 481 northwest of that junction) -- which IMO is the appropriate choice, considering both will be separate freeways, there should be no problem. Now -- signing the original I-81 as a "green" business loop might be dicey, since it would involve three overall segments with a boulevard in the middle. But if the 3di's are retained on the remaining section, NB "I-181" (or whatever) could use "I-181/Downtown Syracuse" with a yellow banner stating "FREEWAY ENDS IN (X) MILES"; southbound, it would read "I-481/Downtown Syracuse/TO I-690".
Something similar would work for the erstwhile "Biz 80" loop in Sacramento: From I-80 westbound at the CA 51/Biz 80 split, the sign would read "South CA 51/Central Sacramento/To CA 99/Fresno"; at the CA 160 exit, the two BGS' would read "South CA 51/To CA 99/Fresno" and "CA 160/Downtown Sacramento". Since it's something of an oblique angle to traffic coming WB on I-80, US 50 need not be cited until approaching the Oak Park interchange. Eastbound on US 50 on the W-X freeway; the signage prior to Oak Park could read simply "North CA 51 to I-80 East/Reno", duplicated on CA 99 north and US 50 west. Simple and straightforward; keep I-305 hidden; no need to confuse things just because FHWA needs some formal record of parvenu.