I've never heard Roman Rd or Caledonian Rd used with an article, and only heard the Old Kent Rd used that way in a song. They're road names I hear a fair amount too. I live near Roman Rd and grew up not far from here, and it's always been Roman Rd without any article.
Maybe it's either a extremely localised regional dialect, or an idiosynrasy. *shrugs* It's not Standard English, or the English of all the London dialects I know of.
One of the things I dislike about grammar is the way so many people don't want to admit that any grammatical patterns actually exist. Give an example of one pattern, and someone will come up with ten exceptions as examples of how the pattern doesn't count, as if the millions of examples where the pattern does work are somehow cancelled out.
It's true, a grammar rule (descriptive, not prescriptive), is only useful if it's describing something that happens in the real world; in the real world, the vast majority of place names follow the patterns I outlined earlier, ergo, it is a useful rule/guideline/pattern to follow.
'Human beings have two kidneys.'
'Yeah, but I know someone who has only one kidney!'
'OK then, you're right, obviously it's not at all true that human beings have kidneys, it must all be coincidence.'
'The Beatles were musicians.'
'No they weren't! They made a film too.'
'OK then, they weren't actually musicians at all, it's just a coincidence that they played music a lot.'
Really. No-one would deny that, say, German has guidelines for when to use the article and when not; why deny that it happens in English too?
But I do like the idea of a person from the Gambia being called a Gambio.
