Roads? Where we're going we don't need roads.
I say that as a joke but it's actually possible. If the government hadn't monopolised infrastructure, the market may have moved in a completely different direction. But now we'll never know.
Back to the real world: private companies would build the roads like they do now. But who would pay? Maybe homeowners associations, maybe businesses who want people to be able to travel to and from their stores, maybe we would see more toll roads. Just a few ideas.