Whether the word "the" should be used to identify an 1nterstate or highway... "it ain't where your're from, but where you're at."

My family is from the Bay Area, and for years we referred to Highway 101 as "Highway 101" and Interstate 5 as "Interstate 5" or "I-5". Now that my family has relocated to SoCal they now refer to interstates and highways as "THE 101" and "THE 5", etc...

BTW, SoCal is the only place I've heard "the" used in this matter.