Makes sense to me, I hear the definite article prefix far more often in SoCal than NorCal/SF Bay.

Back in IL nobody did this, at least not when I lived there over a decade ago.

Illinois is weird in this regard. In Chicago most of the big freeways have names as well as highway numbers that are used with articles in spoken language far more often, even on the TV news. So it’s “The Kennedy, the Ryan, the Edens, the Ike” instead of say “I-94” or “94”.

A notable exception is Lake Shore Drive (US Highway 41) which everyone just calls “Lakeshore” in conversation with no article.

That's true about the named highways near Chicago.

I grew up out in the west suburbs, everyone just said "88" "53" "59" "355" "i80" etc.

I've lived here (Chicagoland) since 1965 and most often called LSD as well as "Outer Drive".

Everyone I talk to calls it LSD.

I’ve lived here nearly 50 years, and even had a Lake Shore Drive address for a few years. LSD isn’t very common at all in my experience. Cabbies in particular all say “Lakeshore” or “Should I take Lakeshore?”. Same with traffic reports on WBBM etc. Everyone who lived in my building said “<numbers> Lakeshore” when asked where they lived.

The economy of two syllables instead of three wins I guess.