Prefacing each freeway number with "The"
Sigalerts
short cut culture - they are like secret snow skiing powder stashes
Hollywood definitely contributed to this with shows like CHIPS and movies like "Speed" - it's interesting how life in SoCal really does revolve around freeways more than anywhere else in the United States.
SoCal had the first freeways, and they weren't numbered back then. They were named after the areas they traversed, such as "The Arroyo Seco Parkway" or "The San Diego freeway" and so on. When freeways started to get built nationwide the naming convention was changed to a numbering system, and California adopted it to go alongside the existing names (we still have the freeway names on most of our signs).
So in reality, California adding "The" to the front was always correct, every other state is just doing it wrong :)