I had that happen to a car I had once. The glass
guy told me that they have to be replaced. He
said they might not spread for a long time or it
could just go all of a sudden. You just never
know. Of course he was probably trying to sell
me glass too. Not sure on that one. I do know
that here in Ca. it is illegal to have any crack
in the windshield. Driver or passenger side, no
matter, you get a ticket.