Both rail and bus are heavily subsidized -- buses come nowhere close to paying for either their operating or capital expenses with fare revenue. It is probably true that if you broke down the WMATA budget and looked at the degree of subsidy per passenger mile on rail vs. bus, you'd get a higher number for rail than bus, but it's tricky to do an apples-to-apples comparison because the rail figure will include the cost of the stations, tunnels, and track, whereas the bus figure won't include the cost of the roads, but the government pays for the roads too, just not as a line item within the transit agency.

The reason to subsidize rail is that if you didn't, many people wouldn't take the train, they would drive or take the bus, and we don't have the road capacity for that. Rail is an exceptionally efficient means of moving lots of people with not very much space, and drivers and bus riders benefit from those people having been moved off of the roads in the form of reduced traffic.

That might be a relevant point in some cities, mainly New York. But in the DC metro area, only a tiny fraction of commuters take rail to begin with, in part because Metro is geared to getting people in and out of DC while most jobs in the area are outside DC. I’ve always found it very odd that folks who work ordinary jobs in the suburbs subsidize the relatively high income professionals that work in DC and can afford to live near a Metro stop.

> only a tiny fraction of commuters take rail to begin with

If you define "metro area" expansively, that's true, but rail mode share in the closer-in suburbs (Montgomery county, Arlington county) is decently high, and individual counties' contributions to WMATA's budget are commensurate with use. Not many people in Loudoun county use metro, but they also don't contribute very much, and nobody it Charles county does, but they don't contribute anything.

WMATA is at the low end of the farebox recovery ratio (42%). Meanwhile SF's Muni is at 35%, BART at 70%, and Caltrain at 63%.

Life and government isn't this simple. Subsidizing metro draws in high-income earners and thus builds the economy and increases tax revenues. The stratospheric price of housing near Metro stations increases real estate tax revenues as well.

The increased cost of housing near transit also reflects that various costs associate with sprawl no longer have to be funded (e.g commute time, roads).