Funny this thread should come up.
I've spoken to countless people from Northern Cal and all the way east of California and found that So. Cal. people are the only ones who tend to put "the" in front of highways. Once I started realizing this by way of a buddy of mine (who is not from California), I was more aware of myself and tried to stop using "the" in front of highway names. I've even begun correcting people. My "location" is a total joke that I stuck on a few days back as a joke really.
Honestly, I'd like to say that putting THE in front of highway numbers somehow caters to the overall pertentious nature of so. cal. people finding themselves more important than the rest of the world. Perhaps this is my perception of the very area I was born and raised in, but it is my perception to have.
Either that or we're just attached to the word "the" and we find it to be so important that is must go before just about everything. "the oc" "the 5". 
I've spoken to countless people from Northern Cal and all the way east of California and found that So. Cal. people are the only ones who tend to put "the" in front of highways. Once I started realizing this by way of a buddy of mine (who is not from California), I was more aware of myself and tried to stop using "the" in front of highway names. I've even begun correcting people. My "location" is a total joke that I stuck on a few days back as a joke really.
Honestly, I'd like to say that putting THE in front of highway numbers somehow caters to the overall pertentious nature of so. cal. people finding themselves more important than the rest of the world. Perhaps this is my perception of the very area I was born and raised in, but it is my perception to have.