In order to evaluate transport methods one must factor in all costs. That is notoriously difficult to do, mostly because proponents of cars (eg: capitalist / feudal organisations like Ford et. al.) prefer to bury the truth, lobby governments for free resources, and lie all the way to the bank.
Why did early mass transit systems in America fail?
Answer: They didn't. They were entirely successful until car companies bought them up and bankrupted them.
Why do cars look like a good mode of transport?
Answer: Because all the costs of roads, environmental pollution, fuel subsidies and so on are born by the regular taxpayer. The capital costs of rail (for example) are seen as too expensive while far greater amounts of money are spent on cars.
Ivan Illich showed the true cost of the bicycle makes it the most efficient mode of transport. Mass transit is less so, and cars are the worst offenders.
Mass transit is not acceptable because people have been duped into associating cars with "freedom". But the mass murder caused by these vehicles is apparently acceptable in the name of capitalism.
Well, mass transit is one of the largest corporations which need a lot of money to keep on going, and where they get all that money from, well our taxes obviously.