I take their meaning to be this: right now, the government subsidizes a form of transportation because there's no effective way for the costs of allowing it to

I take their meaning to be this: right now, the government subsidizes a form of transportation because there's no effective way for the costs of allowing it to be internalized. (Having a toll plaza on every intersection is obviously impossible.) With driving cars, it will become much cheaper to engage in trade centered around automobile transit. Sensors, tracking, mutuality agreements between road owners and car makers. It's plausible that all existing transit subsidies could accumulate to the road owners through market pricing, not government handouts that we have difficulty establishing the true value of.