Las Vegas street name colloquialisms

I realized today that we in Las Vegas have a few streets which are said a specific way, and while outsiders would understand us, they might not say the street names in the same way as a person who has lived here for a while.

Most, if not all, of the streets in this city have a suffix — Ave, St, Blvd, Way, etc. When giving directions or stating the location of a landmark, no one ever says “Oh, it’s located on Rainbow Boulevard” or “You’ll turn left down Tropicana Avenue”; these suffixes are dropped.

However, there are a few streets in the city for which one Must Always affix the suffix. The three that sprang to mind today were:

Maryland Parkway, Boulder Highway, and Las Vegas Boulevard. You’ll never hear a Las Vegas native say just “Maryland” or “Boulder” or “Las Vegas” — you just won’t.

We also refer to I-215 as “the two-fifteen”… but I’ve heard other cities do this with their freeways. Sometimes we call US-95 “the ninety-five” and I-15 “the fifteen,” but I don’t think I have ever heard “I-215″ in colloquial speech. It’s always just “the two-fifteen”

Anyway, I just thought it was interesting that we do that, and wondered why. Does anyone know? And are there any other streets around town with similar “rules”?