How fuel-efficient is public transport, really?

[Skywatcher]

@Sailboat

Where I live, county buses feed commuters to the Washington, DC Metro subway system. They are tributaries to that great river. The subway is, in turn, even more efficient than buses, so the buses feeding the Metro would be saving highway space and energy even if they themselves ran at a loss (up to a point).

And Metro is phasing out its diesel buses in favor of ones that run on natural gas.