My thinking is this is two-pronged. It won't make sense to make the infrastructure investment until there are sufficient proof points that this is 1.) something people want and 2.) something that's economically viable.
It's likely that the early geofenced version of passenger autonomy will demonstrate what further infrastructure is needed and how much it would cost.
One interesting side point; dedicated lanes for autonomous traffic are already being proposed on some roadways, particularly interstates in the U.S and highways in Europe. The economic benefits from autonomous logistics (e.g. trucking) are more readily capturable, so the infrastructure investment might make more sense there up front.