I knew an older woman who had a hard time remembering freeways by their numbers but could remember them all by their names (e.g. "Santa Ana" freeway instead of "5"). That seemed odd because to me the number was the name, so why be any different?
I’ve heard a couple of LA natives say that’s an explanation for SoCal’s affinity for calling them “the 5”: they switched from “the Santa Ana”.
This is interesting to me because here in Iowa, the Lincoln Highway is "old Highway 30". In the 60s they rerouted Hwy30 about a mile south of the existing Lincoln Way so they could make it 4 lane and avoid towns.
The part I thought was interesting is I assumed it would have the same number designation across the entire nation, but that doesn't appear to be the case.