"Today, The Tennessean reports that commuter-rail planners in the Nashville area are looking at a gas tax increase to help subsidize their guaranteed-to-be-a-money-loser project."

As opposed to which money making transit projects (other than perhaps toll roads)? I know of no bigger sink hole of public dollars than highway spending (and that is even before you consider the grotesque negative externalities).

People use roads and pay for them via the gas tax.

Very few people will use mass transit, and their fares will cover very little of the capital or operating costs and it will have to be subsidized by government at a very costly rate per person transported.

If only that was the case. Looking at TDOT's numbers (http://www.tdot.state.tn.us/GasTax/), the taxes on gasoline fund less than half of TDOT's highway maintenance.

Finding data quickly is hard, but it seems that in 2000 alone, $19,574,136 in general funds, $6,115,454 in property taxes, and $11,301,073 in bond receipts funded highway expenditures (https://www.fhwa.dot.gov/ohim/hs01/hf1.htm).

Given this limited data, I'm not willing to accept without further proof that "People use roads and pay for them via the gas tax."

(And, again, those direct expenditures do not reflect the mammoth indirect costs of highway expenditures. See, e.g., http://www.agenda21.ee/english/transport/landuse_costs_extern.pdf.)