[cassowary]

Hi. We're I'm from, we mostly say the plus the name of the road. So "take the Monash". But the Monash is officially "Monash Fwy". It's also called the M1. Country roads often have long names like "Main Neerim Road" or "Warragul Korumburra Rd". When I've had to give a direction involving them, I say "just before you enter town, turn left towards Warragul" because there will be a giant sign in Korumburra pointing towards Warragul; if you're in the middle of the road, you have a sign pointing to Korumburra and another pointing to Warragul.

Such roads often have numbers. But I've never committed them to memory or used them in ordinary conversation. Based on the precedent of the "M1", I guess I'd expect "the C520" or whatever. But that recommendation is probably not worth the paper it's printed on.