I've never seen a split longer than 1/2 inch *pauses to check ruler* 1/4 of an inch long in my hair - and I've seen my hair with triple splits on a single strand.
If you think about it, most splits aren't 'perfectly' in the middle of the strand of hair - they start off center, as it is, because it's caused by the cuticle (which is the outermost layer) breaking away.... A strand of hair isn't that thick, so when the split starts off center, it's going to travel part of the way up the strand, and then break away, because there won't be enough 'hair' attached to hold the split side onto the strand side.
I suspect that split hairs are the reason for MOST of my breakage - esp. the really tiny, super fine looking hairs.
I've always heard that 'splits will travel all the way up your strand', but I really don't see how that's possible....