Why do Southern Californian’s put a “the” before the freeway number?
The Los Angeles region was an early adopter of freeways, even before the National Interstate and Defense Highways Act of 1956. These early freeways became known by their purpose. You were going to San Bernardino, you got on “the” San Bernardino Freeway, which, overtime, became just “The San Bernardino,” as did “The Hollywood, ” “The Ventura,” etc.
Then came the interstate system and the need to identify these freeways by numbers. Eventually, the number of the freeway eclipsed the name, but the “the” remained and became a part of the SoCal vernacular…the 5, the 101, the 405.