A long time ago, on a planet far far away, we used to use a lot more research, analysis, and math to try to figure these things out.

The best resource for the math and engineering of all things public transport is Vukan Vuchic's Urban Public Transportation Systems and Technology, which includes the theoretical, the observed, the operational and engineering equations, the costs, the ridership ranges, the benefits, and how to calculate them, with the "fits" of these theories and models to the observed operations of every mode of public transport, from shared ride systems to every form of "fixed guideway.

Todd Littman's Victoria Transportation Policy Institute web site is another great source of published papers that attempt to quantify costs and benefits of various urban transport policies. I don't buy into all of it. There's an occasional "faith based" new "urbanist "result that might prompt an alert on my poor methodology (aka BS) detector. But, it is out there for folks to decide for themselves. And, he is pretty rigorous at putting out a lot of mostly good quality research, including many things related to rail system performance, tradeoffs, and impacts.

I would have more confidence in how we are making these decisions, if so many these days, didn't appear to be coming from folks selling the most recent popular "fad" brand of "faith based" or "visionary" transportation "policy" solutions, to address real world transportation questions that we can readily answer with good research and analysis...….