It's a regional variation. In California, where I grew up, it was "take the 101 north", "get on the 405", and so on. In Pennsylvania, where I now live, it's "take 202 north", "get on I-95", and so forth. Note that this only applies to numbered roads, really -- in both places, named roads get the article: "the Schuylkill", "the Hollywood freeway", "the Blue Route", "the Pacific Coast highway".

I don't know where the dividing line is for the different usages, nor do I know what they do in other English-speaking countries. I'll ask my husband what they do in Indiana (where he lived for a time); that's reasonably central.

It's a regional variation. In California, where I grew up, it was "take the 101 north", "get on the 405", and so on. In Pennsylvania, where I now live, it's "take 202 north", "get on I-95", and so forth. Note that this only applies to numbered roads, really -- in both places, named roads get the article: "the Schuylkill", "the Hollywood freeway", "the Blue Route", "the Pacific Coast highway".

I don't know where the dividing line is for the different usages, nor do I know what they do in other English-speaking countries.

My husband reports that local usage in Indiana (where he lived for a time) does not use the definite article on numbered roads. Friends who lived in Florida report the same thing.