How do you say the name of the main highway that passes through the Central Coast? It may depend on where you or your family are from Northern or Southern California.

“The official name for the highway is U.S. Highway 101,” said Jim Shivers, a spokesperson for Caltrans District Five.

While that may be its legal name, you rarely hear that in everyday conversation. Instead, it’s typically shortened to either “101” or “The 101” depending on where somebody is from.

In Southern California, the definite article “the” gets placed before just about every freeway or highway, whereas in the Bay Area just the numbers are said. So in San Luis Obispo, roughly the halfway point between the two big metros, the freeway references collide.

The issue fascinates longtime Bay Area traffic anchor Joe McConnell who told KCBX that he recognized the north/south split early in his career.

“And it took me a while to realize that that derives from how most freeways in Southern California have names and that they use those names," McConnell said, giving examples such as the Hollywood and San Diego Freeways. “So, when using the number, they just extend the article 'the' to the number."

McConnell said Bay Area freeways also have names, and in most cases they’re named after people.

“We just use very few of them and the number becomes the name," McConnell said. "So, it's just 101, 80, 680 and 580."

McConnell may be onto something. Nathan Masters, a writer specializing in Los Angeles history at USC, has researched the 'the' issue. He said — as McConnell surmised — the structure evolved over time.

"People were calling freeways by their names and they were using specifically the shorthand, so they didn't just say 'I'm taking the Santa Ana Freeway' they were saying 'I'm taking the Santa Ana to the San Bernardino to the Hollywood," said Masters.

Masters said this shorthand practice then carried over to the freeway numbers, giving us the trend we hear today.

Masters said Southern California is rare, but not unique in this category. He said the Phoenix and Toronto/Buffalo areas also use 'the' before saying freeway or highway numbers.

There are no studies to show what the preferred freeway reference pattern is for California residents living along the Central Coast, but typically, the closer you get to either main urban center — Los Angeles or San Francisco — the more you start to hear that region's influence.