From an economic standpoint, investing in fast mass-transit (e.g. high speed rail) would probably result in a larger net positive than self driving cars. Why?

From an economic standpoint, investing in fast mass-transit (e.g. high speed rail) would probably result in a larger net positive than self driving cars. Why? 1. I would theorize that the economic benefits of transportation are directly proportional to how fast the service is, and how much people it can move. As an estimation, I'd say cars are limited to 60 mph while high speed rail would be limited to 200 mph. 2. With fixed-path mass transit, the problem of traffic is greatly simplified. Self driving cars may solve a labor issue but they won't solve the traffic problem: cars routing themselves selfishly will not result in the lowest travel time possible. You can argue that a central coordinator can exist to coordinate routes, but if there's an incentive for a person (not necessarily a driver) to deviate from their set path, why wouldn't they take it?