I grew up in LA. I took the 405 to get anywhere outside the community I lived in. When I arrived in Berkeley for college, I was surprised by the frequency with which people would argue if one should, e.g., take 80 to get to San Francisco, or if one should take the 80.
When a city planner is planning a new community, he/she creates a grid of streets for people to use to get around. However, people don't think of streets as a network. They think of individual streets. For example, to get from one person's house to another's, you might take Milvia north, turn right on Hearst, and turn left on Spruce. You wouldn't prefix any of these names with an article, because these are the names of the streets. People think of streets individually. Milvia is a street that one of my friends lives on. Hearst is a road that you travel down to get from one place in Berkeley to another.
People who live in Northern California think of highways as they think of streets. They are individual roads that one takes to get from one location to another. 80 is the name of one of these roads. One would never say "I'm driving down the University Avenue", so why would one say "I'm driving down the 80"?
Public transportation is another matter, however. The 52L is not distinguishably different from the 43. When someone takes a bus to get from one place to another, he or she is taking the bus. The only time someone would bother to distinguish which bus would be to instruct someone which bus route to use to get around. In that case, someone would say, "Take the 52 to get from campus to the supermarket." 52 is a description of the bus route. It's an adjective to distinguish a bus that goes one direction from one that goes another. However, when thinking about busses in general, people don't ordinarily distinguish between them.
If you're in a government office and you're filling out forms, someone behind a desk might tell you to fill out "the blue form" to distinguish the form you want from the one that's yellow or the one that's green. "Blue" is an adjective that describes and specifies which form you should be interested in, but it is not the name of the form. This is why the person behind the desk wouldn't say "fill out blue form." This statement doesn't sound right. Similarly, someone wouldn't say "take 52 to get from campus to the supermarket."
People in Southern California think of their freeways like people in Northern California think of their busses. The freeways in LA, for example, form a network that one uses to get around the city. The entire network is "the freeway". If I want to go to my grandmother's house, I'll take the freeway. The thinking behind this is similar to the thinking behind busing from campus to the market. If I wanted to make this trip, I'd take the bus. If someone wonders how they'd make the same trip from campus, I would say "take the 52." Similarly, if someone wanted to know how to get to my grandmother's house, I'd say "take the 101."
I started by describing streets as a grid that people use to get around. This would imply that streets are a network. By the reasoning above, this would mean that it is correct to refer to "the University Avenue." However, people don't think of streets as a network. Each street is different from every other street. My friend lives on Milvia. The supermarket is on Cedar. People think of streets as places that buildings are built on, rather than a network of roads that people use to get around town. In fact, this is the main purpose of having streets. Though major streets and boulevards may be designed with travel rather than construction in mind, most streets are thought of as places where houses or businesses are built. By this way of thinking, the streets aren't a system. My friend does live on the same street as the school, because it's one continuous road, but he does not live on the same street as me, even though we live on the same network.
The purpose of freeways is different from that of streets. Many years ago, Congress decided to create the highway system to allow people to easily travel from one city to another. Each highway is not an individual road; the entire system was created to get around the country.
I picked my maps above carefully. The LA map shows the freeways, but doesn't show any streets. Streets and roads are not the same to someone from LA. The Oakland map shows both freeways and streets. To someone from the Bay Area, they're both roads you drive down to get around.
So, who's right? Is the freeway just one big system that people use to get around town, or is each freeway its own road that deserves its own name? The correct answer is that everyone's right. There aren't as many freeways in Northern California, so it's correct to think of each one as a separate road that one would travel down to get across town. However, the freeways definitely form a network in Southern California. There are so many freeways that nobody bothers to distinguish them in their mind.
Unfortunately, this answer doesn't satisfy many people, because everyone wants to think there is one correct way to refer to a freeway. If you're one of these people, then I say to you that the people from Southern California are correct. As I said above, there is no good reason to think of each freeway as a separate road. There is nothing distinguishable between 80 and 580. They're both part of the same freeway system. The same way you'd refer to the right lane, the UC Berkeley website, or the financial aid office's phone number, you should refer to the 101 freeway.
Like I said before, if you're from Northern California, you can go ahead and call your freeway 80 for all I care. You think of it as the name of a special road, and that's fine with me. But as far as I'm concerned, I'll always drive down the 5 to visit home.
Brian Wolf