Where a state route is shared with a well-known local street name in a metro, what is the changeover point where locals change from calling it by the route number to the street name?
In Minneapolis/St. Paul, I would say MN 47/"Highway 47" is only used in parlance north of US 10, and "University Ave" the whole way south of 10; for MN 65, though the Central Ave designation extends a ways north of US 10, I think it's generally called "Highway 65" north of US 10 and "Central Ave" south of it. MN 5's changeover from "Highway 5" to "West 7th St" is right at the end of the freeway heading northeast into St. Paul.
The idea is for lengthy routes that aren't entirely coterminous with a street; for example something that doesn't fit is MN 51/Snelling Ave, because it's only known as Snelling Avenue (or Montreal Ave for the short jog at the south end) in local parlance and never called MN 51 by locals.
An example near me is US 22/OH 3 (Montgomery Rd). Montgomery Rd is officially used in addresses until around Columbia Rd, where it switches to addresses with 'US 22' as the street name, though it's sometimes called by the name north of that. A common marker I see people switch from mostly calling it "Montgomery Rd" and 'US 22' is where the road crosses the Little Miami River, about 1.8 miles north of the Columbia Rd intersection. And then there's other people that doesn't call it by its road name at all, and only 'US 22', 'Route 22' or 'Highway 22' (never heard anyone call it solely as OH 3 or its speaking variants before).
US 70S on the west side of Nashville, TN is called Hwy 70S until some point just east of Old Hickory Blvd. It used to be around Brookfield Terrace but I have seen some Harding Pike signs west of there now.
In Florida for SR 37 the change from Florida Avenue in Lakeland to plain ole Highway 36 at Pipkin Road.
In Northwest Indiana:
Indianapolis Blvd (US 12/20/41, then US 12/20, then US 20 then IN 152, then US 41) is known by its name down to the Highland/Schererville border, and then by US 41 south from there.
Cleveland St is know by its name down to 61st Ave and then IN 55 south from there.
US 30 is officially known as Joliet St in Dyer and 81st Ave in Merrillville, but almost everyone just refers to the entire route as US 30.