Good question. The US Highway government website acknowledges ferries being an important part of the Highway transportation system. https://highways.dot.gov/public-roads/marchapril-2014/where-water-meets-road
I’m not sure if that the same as what you are asking, that’s it’s part of the US Highway system, but it’s certainly at minimum a connector.
I’m guessing in NY the ferry system has government subsidies either local or federal if it needs money to function. It’s a big commuter route in NYC.
A long time ago I looked up municipal buses and if they worked in the red or the black, and it was mostly in the red, with some above water. Light rail trains usually need some subsidy also. I’m guessing many of the large ferries also receive money being acknowledged as an integral part of the road system.