>>
>> I'm not wondering about the number, but the use of the definite article.
>> Elsewhere people say "95" or "I-95." I've never heard anyone say "The 95."
>
>
> It's because people in southern California spend so much time on freeways
No more time than people in Houston do, so this won't do as an explanation. Chicagoans actually have longer average commutes than Angelenos and they don't call it "The I-94".
-j