To be fair, it’s an oddity from an American perspective. Our highways are numbered, some streets are numbered but most are named, and it’s vanishingly rare that a street will have both a number and a name.
So, let's take Route 66. Are you telling me that none of that route had a name? Or did they go along while adding Route 66 signs and take _out_ existing names for the roads used?
Did people wake up one day and find that their "Main Street" was now just "part of Route 66, it doesn't have a name" ?
The letter-number designations like "A33" in the UK are like your route numbers. Some were purpose built and nobody cares what the underlying road is "named" (all the major Motorways are like this, there is no "name" for the M25, it's just the M25) but most are pre-existing roads, designated as part of some route and to locals the original name is what they'd call their bit.
e.g. Nobody where I live would say "the A335" they'd say "Thomas Lewis Way" because that's what this part of the A335 is named even though it was constructed specifically in order to bypass local streets for the A335 route. A person from out of town might say they used the A335 but probably people would look puzzled, then go "Oh, Thomas Lewis Way, yeah".
> So, let's take Route 66. Are you telling me that none of that route had a name?
In the Midwest, at least, it is very common for larger roads to have both local names and route numbers (one of county, state, or federal); no, the road name is not removed that I've ever seen. An example, heading due west from Chicago is state route 38, which is Roosevelt Road through the city and suburbs, then has other names as it passes through smaller towns - often "Lincoln Highway," as 38 generally follows that historic route. Frequently state routes will have the name "State Street" within smaller towns.
The Interstate system is a departure from this, and rarely do they have names - although in Chicago they do have de facto names, which often confuses outsiders when they hear the traffic report. "What the heck is the Ike?!"
I’m not sure if the UK is the same as here, but in Australia the reason you have both for major roads is that generally you have regular names, and then the letter/number is the route designator. A route will generally traverse multiple streets/roads/motorways. So in the state I live in if you follow the M1 you will go from the Pacific Motorway at the southern border, onto the Gateway Motorway and then on to the Bruce Highway. So they have different roles.
Around here (Boston) there are many roads with both a name and a number. Route 16 is the Mystic Valley Parkway, and then later on that splits off and 16 is the Alewife Brook Parkway. Or, Route 60 is also High Street, at least by us. For these two think we use the number a bit more, but the name is also used. Other roads, like Route 2 are called that in some sections but not others (no one would call Memorial Drive "Route 2"). Even the interstates have names that no one would use: Route 128 is the "Yankee Division Highway", but everyone says 128 (or maybe 95). And some interstates have names people do use: the Mass Pike (Massachusetts Turnpike) can be called "90" but generally isn't.
Overall, this is complicated and it's not surprising to me that it's hard to get a computer to do the right thing.
