[int_19h]

Here in WA, it seems that for single- and double-digit numbers, people usually prepend the prefix - so it's also I-5, not just 5; and I-90, not 90.

But for multi-digit, it's virtually never there - it's 405 and 520 (without "the"!), not I-405 and WA-520.

Now that I think about it, it's probably not so much about the number of digits, as it is about the number of words. So I-90 gets the prefix because "ninety" is a single word, but I-95 somehow sounds strange.

[spc476]

Up in Detroit (I have family there) almost everyone talks about 75 (I-75). Down here in South Florida (where I live), it's always I-95. Just "95" sounds strange to me, as well as "I-75".

I guess it's what you grew up listening to.