User blog comment:Zombiekiller14/My Left 4 Dead 3 Plot/@comment-2086708-20101201140345

They probably encountered the Infected just like the L4D1 and L4D2 Survivors before they met each other.

And FYI, between Death School and Riverbound, they had a short drive after escaping the school, and stopping at the bridge. And BTW, I change the campaign name to Riverbound.