Interesting article here on the Southern California linguistic tradition of including a definite article in front of freeway identifiers, whether it's a descriptive name ("the San Diego Freeway") or a number ("the 405").
It was certainly a change that I had to get used to when I moved from SoCal to Denver, where:
(a) Freeway names, where they exist ("the Valley Freeway"), are largely ignored.
(b) Interstates get prefixed with "I" ("I-25," "I-70") and, sometimes, other types of roads get an identifier ("C-470").
(c) Nobody uses a definite article ("Take C-470 to I-25 to 36").
The post's suggestion as to why SoCal does this (the descriptive names were used for so long with a definite article that the increased use of numbers adopted the same style) doesn't seem to explain why SoCal is different from other areas that were early freeway adopters. But it's still a fun look at the subject, and includes a lovely link to a 1943 freeway planning book (http://goo.gl/YxLRdA) that talks about the coming freeway revolution in the LA area, and how that did (and, in some cases, didn't) come to pass.
(h/t +Kee Hinckley)
The 5, the 101, the 405: Why Southern Californians Love Saying ‘the’ Before Freeway Numbers
How did Southern Californians come to treat their highway route numbers as if they were proper names?
Um…I live in Western New York and would very likely say “the,” as in, “Take the 90 to …” or, “I hate driving the 290.”
Maybe its because I am originally from Southern California, but I am not so sure. I moved to Las Vegas when I was 10, had a short stint back in CA for 2 years, and have been here in Vegas ever since, so I learned about roads in Vegas. I refer to HWYs as the all the time. I don't think its specifically a California things. I also work for AAA and taking roadside calls for people in Arizona, they do the same thing.
When I lived in Riverside, CA, I met some folks from San Diego who asked why I said "the 5" instead of just "5." It seems that not all areas of So Cal do this.
My answer, by the way, was that I always heard it that way on radio traffic reports.
+Scott Randel That;'s certainly part of the answer — if the Official Word comes that way, people will use it that way. I suspect the traffic reporters are the reason why the various names (the Riverside Freeway, the Pomona Freeway, the Santa Monica Freeway) have stuck as well.