[scythe]

>There's only a handful of cities that are massive enough to do projects that would require hiring highly paid specialists to manage these huge projects.

If you use the Census Bureau's broadest definition of economically intradependent regions, the Combined Statistical Areas — defined roughly by commuting patterns, which is the relevant scale for a transit system — there are in fact eleven major cities at populations of seven million or higher: New York, Los Angeles, Chicago, Baltimore-Washington, Dallas, San Francisco, Boston-Providence, Houston, Atlanta, Miami and Philadelphia-Wilmington. Over a third of Americans live in one of these "agglomerations". But establishing a system to handle regional planning would require crossing state boundaries in six of those cases.

There are some advantages to local expertise: the geographic and social factors affecting Miami are very different from those in Dallas, which are both very different from San Francisco, which are all totally unlike New York. Establishing the necessary agencies and securing their purview would require federal action, though, I agree.

[WorldMaker]

> But establishing a system to handle regional planning would require crossing state boundaries in six of those cases.

6 of 11 is more than half of your examples. That alone seems to suggest there would be efficiencies in federally-supervised planning simply to cross-cut inter-state concerns. (Such as with roads, the use of "inter-state" there is not an accident.)

Scrolling further through the list of CSAs the ones between a million people and seven million that are multi-state seem too often to be the least well served by public transportation access today compared to their peers, and that doesn't seem to be a coincidence.