Unless you break American's marriage to SOV, all you are describing is replacing Taxis and TNC with self driving services."Zero impact"? Really??
Cellphone app order-on-demand pod service which will eliminate on-street parking, parking garages, individual driving techniques, etc. will have "zero impact"? Interesting........
Just think of the benefit of 100% street utilization for flow, instead of the current 50-70% utilization due to on-street parking. Given the effects throughout the system from the current 30-50% area utilization of the windy streets downtown and you can imagine the downstream benefits.
Stents that clear arteries make stronger, more effective hearts. Individually owned and cared-for vehicles that clog the sides of the streets are the plaque.
I'm not saying there won't be times of slower mobility with 2+ million living in Boston, but "zero impact" is a clearly hyperbole.
And if you have the same number of SOVs on the road at rush hour, nothing about the traffic situation has changed. Number of vehicles is what matters, not who owns them. And on demand TNC has been shown to make traffic worse, not better, by shifting demand away from mass transit.