I have only read the linked article, not the study, but it seems to me to be a bizarre conclusion that if capacity is increased and utilization remains at maximum, that the capacity caused the utilization.

It seems to be a much simpler scenario that demand far outstrips capacity, and until you can meet the demand, saturation every lane added will continue to be saturated.

I'm sure amdahl's law applies to lane adding here, on top of the fact that all the highways I've seen merge from one side or the other. I don't think I've seen any that merge in the middle, though I guess they probably exist.