When my brother was traveling behind a large delivery truck, he ended up getting a large rock spit into his windshield, and it created a crack that soon advanced into a huge web like pattern in the glass, right in front of his visibility spot on the windshield. He of course ended up having to go to the local Auto Glass Repair Mn shop, in order to have them replace the whole piece of glass. He thought that it was going to cost him an arm and a leg to do so, but they charged him a modest rate and did a great job.