You're implying that there's a direct equivalence, but that's not really true. Although the parent comment said "rail line", since TFA is, specifically, about

You're implying that there's a direct equivalence, but that's not really true. Although the parent comment said "rail line", since TFA is, specifically, about HSR, that's a unique rail line in an existing system, which has something of an all-or-nothing construction problem. Having it half finished won't reduce the train travel time between LA and the SFBA for anyone. Conversely, road capacity can be added incrementally, and, in many cases, when it is, it has an immediate effect for that section [1], providing relief as soon as the money and/or construction resources are available. In rural California, that's more likely to be months and fractions of a billion, not years and billions. The urban parts are slower and more expensive, but only proprotionally so (i.e. HSR is yet slower and even more expensive there, too). You haven't presented any evidence for your assumption that on-demand driverless vehicles would require extra capacity, especially down a long-haul corridor. At best, that's some very heavy speculation on the operating cost (dominated by tires, suspension, electricty, I'd expect) versus capital cost of keeping enough spares in each metro. [1] Yes, I'm aware that, at times, it can have a paradoxically negative effect on congestion, but I'm pretty sure that doesn't happen for capacity increases on what are essentially point-to-point corridors.