Earlier quoted context omitted.
> The correct title for Californians is "The 5". You have omitted the rather important qualifier “Southern” from your description, as that usage is a key differentiator between Northern and Southern California.
I live in the bay area and everyone I know calls it "I-5". "Everyone I know" of course could be biased though as most of my circle did not grow up in California.
— https://www.kcbx.org/post/how-you-refer-us-101-says-lot-abou...