Is that an assumption, or a requirement? It seems to me that autonomous vehicles are based on fitting into the existing infrastructure because that's what they'll have to actually deal with. Any technology which requires new infrastructure hits a chicken and egg problem, since nobody will want to spend on infrastructure without any cars to use it, and nobody will want to buy cars that use it if the infrastructure isn't there.

Seems like it would basically be a two-step process. First, you need autonomous vehicles which work on roads as we have them now. Once they're common, they can start adding features which can take advantage of more sophisticated infrastructure when it comes. Sort of like how early cars had to work on paths built for horse carriages, but once they were common we could start building things like freeways.